C8 IDENTIFICATION OF IONS BY Name: CHEMICAL AND … · 2018-03-29 · This question is about...

C8 IDENTIFICATION OF IONS BYCHEMICAL AND SPECTROSCOPICMEANSQuestion Practice

Name: ________________________

Class: ________________________

Date: ________________________

Time: 164 minutes

Marks: 163 marks

Comments: GCSE CHEMISTRY ONLY

of 60Immanuel+College

This question is about reactions of ethanoic acid and the analysis of salts.

(a) Figure 1 shows the apparatus used to investigate the reaction of ethanoic acid withcalcium carbonate.

(i) Describe a change that would be seen in each test tube.

Give a reason for each change.

Test tube 1 ____________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

Test tube 2 ____________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(4)

1

(ii) Complete the displayed structure of ethanoic acid.

(1)


(iii) Ethanoic acid is a carboxylic acid.Complete the sentence.

Carboxylic acids react with alcohols in the presence of an

____________

catalyst to produce pleasant-smelling compounds

called ______________ .

(2)

(b) Figure 2 shows four test tubes containing three different salt solutions and water.

Each solution and the water was tested with:

• silver nitrate in the presence of dilute nitric acid

• barium chloride in the presence of dilute hydrochloric acid.

Complete the table of results.

Potassium

chloride solution

Calciumnitrate

solution

Ammoniumsulfate solution

Water

Test with silvernitrate in thepresence of dilutenitric acid

no change no change

Test with bariumchloride in thepresence of dilutehydrochloric acid

no change white precipitate

(2)


(c) Flame tests can be used to identify metal ions.

(i) Complete the following sentences.

The flame colour for potassium ions is ____________ .

The flame colour for calcium ions is ____________ .

(2)

(ii) Give one reason why a flame test would not show the presence of both potassiumions and calcium ions in a mixture.

______________________________________________________________

______________________________________________________________

______________________________________________________________

(1)

(Total 12 marks)

Cheshunt mixture is a powder containing copper sulfate, CuSO4, and ammonium carbonate,(NH4)2CO3

(a) A student tested the Cheshunt mixture.

(i) Hydrochloric acid was added.A gas was produced that turned limewater milky.

Complete the sentence.

The gas was __________________________________ which shows

that _________________________ ions are in the mixture.

(2)

2

(ii) Sodium hydroxide solution was added.A gas was produced that indicates that ammonium ions are in the mixture.


The gas was __________________________________ which turns

damp red ___________________________________________ blue.

(2)


(b) Cheshunt mixture is dissolved in water before it is used.When the student dissolved the Cheshunt mixture in water it formed a blue solution.

(i) Suggest how the student knew that copper ions are in this solution.

______________________________________________________________

______________________________________________________________

(1)

(ii) The student tested the Cheshunt solution and the result of the test indicated thatsulfate ions are in the solution.


The student added a solution of ________________ in the presence of

dilute hydrochloric acid and a ________________ precipitate was produced.

(2)

(Total 7 marks)

Read the information in the box and then answer the questions.

Seidlitz Powder is the name of a medicine.

Seidlitz Powder comes as two powders. One powder is wrapped in white paper andcontains tartaric acid (C4H6O6). The other powder is wrapped in blue paper andcontains potassium sodium tartrate (KNaC4H4O6) and sodium hydrogencarbonate(NaHCO3).

The contents of the blue paper are completely dissolved in water and then thecontents of the white paper are added.

The equation which represents this reaction is:

C4H6O6 (aq) + 2NaHCO3 (aq) Na2C4H4O6 (aq) + 2H2O (l) + 2CO2 (g)

(a) Describe and give the result of a test to identify the gas produced in this reaction.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(2)

3


(b) One of the chemicals in Seidlitz Powder is potassium sodium tartrate (KNaC4H4O6).

Suggest why it would be difficult to identify both potassium ions and sodium ions inpotassium sodium tartrate using a flame test.

___________________________________________________________________

___________________________________________________________________

(1)

(c) Some Seidlitz Powder was bought on the Internet. However, when tested, it was found tobe only magnesium sulfate.

(i) Describe and give the result of a chemical test to show that magnesium sulfatecontains sulfate ions.

Test __________________________________________________________

______________________________________________________________

Result ________________________________________________________

______________________________________________________________

(2)

(ii) Magnesium sulfate contains magnesium ions.

Describe what you see when sodium hydroxide solution is added to a solution ofmagnesium sulfate.

______________________________________________________________

______________________________________________________________

(1)

(Total 6 marks)


Read the information about protecting the bottoms of ships.

A Copper-bottomed Investment

From the 16th to the 19th century, the bottoms of many wooden ships were protectedfrom marine organisms by being covered with sheets of metal.

At first lead was used on the bottoms of ships, then copper was used until 1832when Muntz Metal replaced it. Muntz Metal is an alloy of two transition metals,copper and zinc.

Table of data

Lead Copper Muntz Metal

Cost (£/kg) £1.20 £3.20 £2.30

Melting point (°C) 327 1083 904

Stops sea worms attacking wood Yes Yes Yes

Stops barnacles and seaweedsticking to the bottom of the ship

No Yes Yes

(a) Use the information to answer the following questions.

(i) Suggest why copper replaced lead.

______________________________________________________________

______________________________________________________________

4


(1)

(ii) Suggest why Muntz Metal replaced copper.

______________________________________________________________

______________________________________________________________

(1)

(b) A sample of Muntz Metal contains a very small amount of iron as an impurity.

(i) Name an instrumental method of analysis that could be used to detect iron.

______________________________________________________________

(1)

(ii) Suggest why an instrumental method would detect the iron in this sample of MuntzMetal but a chemical method is not likely to be successful.

______________________________________________________________

______________________________________________________________

(1)

(c) Today, ships are made from steel. Steels are alloys of iron, a transition metal.

Give two properties of transition metals that make them suitable for making ships.

Property 1 __________________________________________________________

___________________________________________________________________

Property 2 __________________________________________________________

___________________________________________________________________

(2)

(Total 6 marks)


Alums are salts. They have been used since ancient times in dyeing and medicine and still havemany uses today.

Three alums are shown in the table:

Name Ions present

Ammonium alum NH4+ Al3+ SO4

2-

Potassium alum K+ Al3+ SO42-

Sodium alum Na+ Al3+ SO42-

(a) These alums contain sulfate ions (SO42-).

Describe and give the result of a chemical test to show this.

Test _______________________________________________________________

___________________________________________________________________

Result _____________________________________________________________

___________________________________________________________________

(2)

5

(b) These alums contain aluminium ions (Al3+).

Describe how sodium hydroxide solution can be used to show this.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(2)


(c) Aluminium ions do not give a colour in flame tests. However, flame tests can be used todistinguish between these three alums.

Explain how these three alums could be identified from the results of flame tests.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(2)

(Total 6 marks)

The label is from a packet of Low Sodium Salt.

6

(a) A student tested some Low Sodium Salt to show that it contains carbonate ions andchloride ions.

(i) Describe and give the result of a test for carbonate ions.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(2)


(ii) A student identified chloride ions using acidified silver nitrate solution.

State what you would see when acidified silver nitrate solution is added to a solutionof Low Sodium Salt.

______________________________________________________________

(1)

(iii) Flame tests can be used to identify potassium ions and sodium ions.

Suggest why it is difficult to identify both of these ions in Low Sodium Salt using aflame test.

______________________________________________________________

______________________________________________________________

(1)

(b) Read the following information and then answer the questions.

Salt – friend or foe?

Sodium chloride (salt) is an essential mineral for our health. It is used to flavourand preserve foods. Too much sodium in our diet may increase the risk of highblood pressure and heart disease. Heart disease is the biggest cause of death inthe United Kingdom. Some people claim that excess sodium is a poison that cancause cancer, while others say that more evidence is needed.

Many processed foods contain salt, so it is easy to exceed the recommendeddaily upper limit of about 5 g of salt per person. A ‘healthier’ amount should beabout 3 g. In the United Kingdom many people consume over 10 g of salt eachday.

One way to reduce sodium in our diet is to use Low Sodium Salt. This has twothirds of the sodium chloride replaced by potassium chloride.

A national newspaper asked readers for their views on two options.

Option 1: Ban the use of sodium chloride in foods.

Option 2: Reduce the amount of sodium chloride in all foods to a ‘healthier’ level.

(i) Suggest why Option 1 was rejected.

______________________________________________________________

______________________________________________________________

(1)


(ii) Suggest two advantages and one disadvantage of Option 2.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(3)

(Total 8 marks)

This label has been taken from a packet of My Baby Food.

MY BABY FOOD

Infant milkPure and natural

Closest to mothers’ breast milkContains traces of essential minerals

500 g

One of the minerals in My Baby Food is calcium carbonate, CaCO3.

7

(a) Chemical tests are used to identify elements and compounds.

(i) A flame test can be used to identify calcium ions.What colour do calcium ions give in a flame test?

______________________________________________________________

(1)


(ii) When a flame test was carried out on My Baby Food, the presence of calcium ionswas not seen. A yellow flame was produced.Name the ion which gives a yellow flame test.

______________________________________________________________

(1)

(iii) Suggest one advantage of using an instrumental method to detect the elementspresent in My Baby Food.

______________________________________________________________

______________________________________________________________

(1)


(iv) Name an instrumental method for detecting elements.

______________________________________________________________

(1)

(b) Read the information in the box below and then answer the question.

Calcium carbonate occurs naturally as marble and limestone. They areimportant building materials and are often used for gravestones.

Calcium carbonate is also an essential mineral for good health and ispresent in many baby foods in small amounts.

My Baby Food is recommended as being the closest to a mother’s ownbreast milk. It is given free to mothers in the developing world – without ittheir babies might die of malnutrition.

Responsible Mothers Are Us (RMAU) is a United Kingdom pressure group.They want to ban chemicals in baby foods. The group was founded by MrsI. M. Right who has made a career in ‘goodness’ and is paid from donationsgiven to RMAU by members of the public.

When interviewed, she said: “Calcium carbonate is a chemical and so it is apollutant. My Baby Food must be banned to prevent the mass medication ofbabies. I don’t feed my baby the stuff of gravestones.”

Many people do not agree with Mrs Right’s ideas.

Suggest why.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(3)

(Total 7 marks)

Chlorine and bromine are important Group 7 elements.

(a) Explain why chlorine is added to drinking water.

___________________________________________________________________

___________________________________________________________________

(1)

8


(b) Describe what you would see when bromine water is added to an unsaturated organiccompound.

___________________________________________________________________

___________________________________________________________________

(1)

(c) Bromine can be extracted from seawater. The dissolved bromide ions are reacted withchlorine. Bromine and chloride ions are formed.

(i) Complete and balance the equation below, which represents the reaction betweenchlorine and bromide ions.

Cl2 + 2Br– → _____________ + _____________(1)

(ii) Describe what you see when chlorine is added to a solution containing bromide ions.

______________________________________________________________

______________________________________________________________

(1)

(d) In terms of electronic structure:

(i) state why bromine and chlorine are both in Group 7

______________________________________________________________

______________________________________________________________

(1)

(ii) explain why bromine is less reactive than chlorine.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(3)


(e) What is the result of adding acidified silver nitrate solution to a solution containing:

(i) chloride ions

______________________________________________________________

(1)

(ii) bromide ions?

______________________________________________________________

(1)

(Total 10 marks)


Chemical tests can be used to identify compounds.

The table shows the results of some tests carried out on three solutions, A, B and C.

Solution Flame TestHydrochloric

acidis added

Sodiumhydroxidesolutionis added

Silver nitratesolutionis added

A Yellow

Carbondioxide gasproduced

B Brick-red Whiteprecipitateinsoluble in

excess sodiumhydroxidesolution

Whiteprecipitate

C

Dark greenprecipitate

Use the information in the table to identify solutions A, B and C.

Give the name of:

(a) solution A; __________________________________________________________

(2)

(b) solution B; __________________________________________________________

(2)

(c) the metal ion in solution C. _____________________________________________

(1)

(Total 5 marks)

9


A student investigated food dyes using paper chromatography.

This is the method used.

1. Put a spot of food colouring X on the start line.2. Put spots of four separate dyes, A, B, C and D, on the start line.3. Place the bottom of the paper in water and leave it for several minutes.

Figure 1 shows the apparatus the student used.

Figure 1

(a) Write down two mistakes the student made in setting up the experiment and explain whatproblems one of the mistakes would cause.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(2)

10


(b) Another student set up the apparatus correctly.

Figure 2 shows the student’s results. The result for dye D is not shown.

Figure 2

Calculate the Rf value of dye A

Give your answer to two significant figures.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

Rf value = ______________________

(3)

(c) Dye D has an Rf value of 0.80. Calculate the distance that dye D moved on thechromatography paper.

___________________________________________________________________

___________________________________________________________________

Distance moved by dye D = ______________________

(1)


(d) Explain how the different dyes in X are separated by paper chromatography.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(4)

(e) Flame emission spectroscopy can be used to analyse metal ions in solution.

Figure 3 gives the flame emission spectra of five metal ions, and of a mixture of two metalions.

Figure 3

Use the spectra to identify the two metal ions in the mixture.

___________________________________________________________________

___________________________________________________________________

(2)


(f) Explain why a flame test could not be used to identify the two metal ions in the mixture.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(2)

(g) Two students tested a green compound X.The students added water to compound X.Compound X did not dissolve.

The students then added a solution of ethanoic acid to compound X.A gas was produced which turned limewater milky.

Student A concluded that compound X was sodium carbonate.Student B concluded that compound X was copper chloride.

Which student, if any, was correct?

Explain your reasoning.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(4)

(Total 18 marks)


This question is about chemical analysis.

(a) A student has solutions of three compounds, X, Y and Z.

The student uses tests to identify the ions in the three compounds.

The student records the results of the tests in the table.

Test

Compound Flame testAdd sodiumhydroxidesolution

Addhydrochloric

acid and bariumchloride solution

Add nitric acidand silver nitrate

solution

X no colour green precipitate white precipitate no reaction

Y yellow flame no reaction no reaction yellow precipitate

Z no colour brown precipitate no reaction cream precipitate

11

Identify the two ions present in each compound, X, Y and Z.

X ____________________________________________________________

Y ____________________________________________________________

Z ____________________________________________________________

(3)


(b) A chemist needs to find the concentration of a solution of barium hydroxide.Barium hydroxide solution is an alkali.

The chemist could find the concentration of the barium hydroxide solution using twodifferent methods.

Method 1• An excess of sodium sulfate solution is added to 25 cm 3 of the barium hydroxide

solution. A precipitate of barium sulfate is formed.

• The precipitate of barium sulfate is filtered, dried and weighed.

• The concentration of the barium hydroxide solution is calculated from the mass ofbarium sulfate produced.

Method 2• 25 cm 3 of the barium hydroxide solution is titrated with hydrochloric acid of known

concentration.

• The concentration of the barium hydroxide solution is calculated from the result of thetitration.

Compare the advantages and disadvantages of the two methods.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(5)

(Total 8 marks)


A student was investigating a magnesium salt, X.

The student found that X:

• has a high melting point

• does not conduct electricity

• dissolves in water and the solution conducts electricity.

(a) (i) What is the type of bonding in magnesium salt X?

______________________________________

(1)

12

(ii) Explain why solid X does not conduct electricity but a solution of X does conductelectricity.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(2)

(b) The student dissolved X in water.

The student added dilute nitric acid and silver nitrate solution to the solution of X.

A white precipitate was formed.

Salt X contains chloride ions.

Explain why a white precipitate was formed.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(2)


(c) The student dissolved X in water.

The student added a few drops of sodium hydroxide solution to the solution of X.

A white precipitate was formed.

(i) Salt X contains magnesium ions.

Name two other metal ions that would give a white precipitate when a few drops ofsodium hydroxide solution are added.

1. ____________________________________________________________

2. ____________________________________________________________

(2)

(ii) Describe the two further tests the student would have to do to show that salt Xcontains magnesium ions, and not the two metal ions you identified in part (c) (i).

Give the expected results of each test.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(4)

(Total 11 marks)


In this question you will be assessed on using good English, organising informationclearly and using specialist terms where appropriate.

A group of students had four different colourless solutions in beakers 1, 2, 3 and 4, shown in thefigure below.

The students knew that the solutions were

• sodium chloride

• sodium iodide

• sodium carbonate

• potassium carbonate

but did not know which solution was in each beaker.

The teacher asked the class to plan a method that could be used to identify each solution.

She gave the students the following reagents to use:

• dilute nitric acid

• silver nitrate solution.

13


The teacher suggested using a flame test to identify the positive ions.

Outline a method the students could use to identify the four solutions.

You should include the results of the tests you describe.

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

Extra space _____________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

(Total 6 marks)


The colours of fireworks are produced by chemicals.

© Igor Sokalski/iStock/Thinkstock

(a) Information about four chemicals is given in the table.

Complete the table below.

ChemicalColour produced in

firework

barium chloride green

_____________ carbonate crimson

sodium nitrate _____________

calcium sulfate red

(2)

14

(b) Describe a test to show that barium chloride solution contains chloride ions.

Give the result of the test.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(2)


(c) A student did two tests on a solution of compound X.

Test 1Sodium hydroxide solution was added.A blue precipitate was formed.

Test 2Dilute hydrochloric acid was added.Barium chloride solution was then added.A white precipitate was formed.

The student concluded that compound X is iron(II) sulfate.

Is the student’s conclusion correct?

Explain your answer.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(3)

(Total 7 marks)


Four bottles of chemicals made in the 1880s were found recently in a cupboard during a Healthand Safety inspection at Lovell Laboratories.

Sodium carbonate

Sodium chloride

Sodium nitrate

Sodium sulfate

The chemical names are shown below each bottle.

15

(a) You are provided with the following reagents:

• aluminium powder

• barium chloride solution acidified with dilute hydrochloric acid

• dilute hydrochloric acid

• silver nitrate solution acidified with dilute nitric acid

• sodium hydroxide solution.

• limewater

• red litmus paper


(i) Describe tests that you could use to show that these chemicals are correctly named.

In each case give the reagent(s) you would use and state the result.

Test and result for carbonate ions:

______________________________________________________________

______________________________________________________________

______________________________________________________________

Test and result for chloride ions:

______________________________________________________________

______________________________________________________________

______________________________________________________________

Test and result for nitrate ions:

______________________________________________________________

______________________________________________________________

______________________________________________________________

Test and result for sulfate ions:

______________________________________________________________

______________________________________________________________

______________________________________________________________

(4)

(ii) Suggest why a flame test would not distinguish between these four chemicals.

______________________________________________________________

(1)

(b) Instrumental methods of analysis linked to computers can be used to identify chemicals.

Give two advantages of using instrumental methods of analysis.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(2)

(Total 7 marks)


Low sodium salt is used on food. This label is from a packet of low sodium salt.

A student tests the low sodium salt for the substances on the label.

(a) (i) The same test can be used to identify sodium ions and potassium ions.

Describe the test.

Give the result of the test for sodium ions and for potassium ions.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(3)

16

(ii) It is difficult to identify potassium ions when sodium ions are present.

Suggest why.

______________________________________________________________

______________________________________________________________

(1)


(b) Describe how the student would test a solution of the low sodium salt for chloride ions.

Give the result of the test.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(3)

(c) To test for magnesium ions, the student adds a few drops of sodium hydroxide solution to asolution of the low sodium salt.

A white precipitate is produced.

This test also gives a white precipitate with aluminium ions and calcium ions.

(i) Describe how the student could confirm that the low sodium salt contains magnesiumions and not aluminium ions.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(2)

(ii) Describe a test the student could do to confirm that the low sodium salt does notcontain calcium ions.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(2)

(Total 11 marks)


A student investigated an egg shell.

Trish Steel [CC-BY-SA-2.0], via Wikimedia Commons

(a) The student did some tests on the egg shell.

The student’s results are shown in the table below.

Test Observation

1Dilute hydrochloric acid wasadded to the egg shell.

A gas was produced. The egg shell dissolved, forming acolourless solution.

2A flame test was done on thecolourless solution from test 1. The flame turned red.

3Sodium hydroxide solution wasadded to the colourless solutionfrom test 1.

A white precipitate formed that did notdissolve in excess sodium hydroxidesolution.

4Silver nitrate solution was addedto the colourless solution fromtest 1.

A white precipitate formed.

(i) The student concluded that the egg shell contains carbonate ions.

Describe how the student could identify the gas produced in test 1.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

17


(2)

(ii) The student concluded that the egg shell contains aluminium ions.

Is the student’s conclusion correct? Use the student’s results to justify your answer.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(2)

(iii) The student concluded that the egg shell contains chloride ions.

Is the student’s conclusion correct? Use the student’s results to justify your answer.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(2)

(b) Some scientists wanted to investigate the amount of lead found in egg shells.They used a modern instrumental method which was more sensitive than older methods.

(i) Name one modern instrumental method used to identify elements.

______________________________________________________________

______________________________________________________________

(1)

(ii) What is the meaning of more sensitive?

______________________________________________________________

______________________________________________________________

(1)

(Total 8 marks)


Ammonium sulfate is an artificial fertiliser.

(a) (i) When this fertiliser is warmed with sodium hydroxide solution, ammonia gas is givenoff.Describe and give the result of a test for ammonia gas.

Test __________________________________________________________

______________________________________________________________

Result ________________________________________________________

______________________________________________________________

(2)

18

(ii) Describe and give the result of a chemical test to show that this fertiliser containssulfate ions (SO4

2–).

Test __________________________________________________________

______________________________________________________________

Result ________________________________________________________

______________________________________________________________

(2)

(b) Ammonium sulfate is made by reacting sulfuric acid (a strong acid) with ammonia solution(a weak alkali).

(i) Explain the meaning of strong in terms of ionisation.

______________________________________________________________

(1)


(ii) A student made some ammonium sulfate in a school laboratory.

The student carried out a titration, using a suitable indicator, to find the volumes ofsulfuric acid and ammonia solution that should be reacted together.

Name a suitable indicator for strong acid-weak alkali titrations.

______________________________________________________________

(1)

(iii) The student found that 25.0 cm3 of ammonia solution reacted completely with32.0 cm3 of sulfuric acid of concentration 0.050 moles per cubic decimetre.

The equation that represents this reaction is:

2H2SO4(aq) + 2NH3(aq) → (NH4)2SO4 (aq)

Calculate the concentration of this ammonia solution in moles per cubic decimetre.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

Concentration = _________________ moles per cubic decimetre

(3)

(iv) Use your answer to (b)(iii) to calculate the concentration of ammonia in grams percubic decimetre.

(If you did not answer part (b)(iii), assume that the concentration of the ammoniasolution is 0.15 moles per cubic decimetre. This is not the correct answer to part(b)(iii).)

Relative formula mass of ammonia (NH3) = 17.

______________________________________________________________

______________________________________________________________

______________________________________________________________

Concentration = _________________ grams per cubic decimetre

(2)

(Total 11 marks)


(a) Four bottles of chemicals made in the 1880s were found recently in a cupboard during aHealth and Safety inspection at Lovell Laboratories.

19

The chemicals are correctly named.

You are provided with the following reagents:

• aluminium powder

• barium chloride solution acidified with dilute hydrochloric acid

• dilute hydrochloric acid

• silver nitrate solution acidified with dilute nitric acid

• sodium hydroxide solution.


(i) Describe tests to show that these chemicals are correctly named.

In each case give the reagent(s) you would use and state what you would see.

Test and result for carbonate ions:

______________________________________________________________

______________________________________________________________

Test and result for chloride ions:

______________________________________________________________

______________________________________________________________

Test and result for nitrate ions:

______________________________________________________________

______________________________________________________________

Test and result for sulfate ions:

______________________________________________________________

______________________________________________________________

(5)

(ii) Suggest why a flame test would not distinguish between these four chemicals.

______________________________________________________________

(1)

(b) Instrumental methods of analysis linked to computers can be used to identify chemicals.

Describe two advantages of using instrumental methods of analysis.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(2)

(Total 8 marks)


Mark schemes

(a) (i) fizz / effervescence / bubbles

allow calcium carbonate decreases in size or dissolves1

because carbon dioxide produced / released

allow because gas produced / released1

limewater turns cloudy / milky / white1

because (a precipitate of or solid) calcium carbonate forms

allow because of carbon dioxide if not already credited1

1

(ii)

allow -OH

do not allow lower case ‘h’1

(iii) acid

must be in this order

ignore any name of an acid1

ester(s)1

(b) white (precipitate) no change

no change no change

all four correct 2 marks

any two correct 1 mark2

(c) (i) lilac

allow purple1

red1

must be in this order

(ii) colours are masked / changed by each flame colour1

[12]


(a) (i) carbon dioxide / CO212

carbonate / CO32-

answers must be in the order shown

marks are independent1

(ii) ammonia / NH31

litmus



(b) (i) solution is blue

accept blue precipitate only if sodium hydroxide added

allow blue liquid

allow copper sulfate / copper ions are blue1

(ii) barium chloride / BaCl2

allow barium nitrate / barium ions / Ba2+

1

white



[7]

(a) limewater / calcium hydroxide13

(limewater) goes milky / cloudy

do not allow this mark if lime water added to solution or powder

or

gives white precipitate / solid1

(b) eg flame colour of (Na) and flame colour of (K) interfere / mask / mix witheach other

accept difficult to determine the colour

or

hard to distinguish

accept some indication that two distinct colours are not seen1


(c) (i) barium chloride (solution) / BaCl2ignore mention of acidification but

do not allow sulfuric acid.

wrong reagent = no mark1

white precipitate / white solid

allow white barium sulfate

or

barium sulfate precipitate1

(ii) white precipitate / white solid

ignore goes milky

do not accept any mention of precipitate dissolving1

[6]

(a) (i) it = copper

(copper) stops barnacles / seaweed (sticking)

accept lead doesn’t stop barnacles / seaweed (sticking)

ignore all other properties1

4

(ii) it = Muntz Metal

(Muntz Metal) is less expensive / cheaper / cheapest

must be a comparison

accept copper is more expensive

ignore other properties1

(b) (i) atomic absorption spec(troscopy) / spectrometry or mass spec(trometry) /spectroscopy

accept spectroscopy / spectrometry alone

allow AAS / MS

do not allow NMR spectroscopy

or IR spectrometry or chromatography1

(ii) it = instrumental method

sensitive or detect (very) small amountsor only small sample needed

allow (more) precise

ignore accurate

allow converse for chemical method

ignore metal contains small amount / low concentration of iron1


(c) any two from:

transition elements (= they)

• unreactive / not very reactive

allow does not corrode

ignore reference to rust

• strong / hard

ignore tough / durable / hard wearing

• malleable / easy to shape

ignore ductile / density / melting point2

[6]

(a) (acidified) barium chloride / nitrate

incorrect reagent or no reagent = 0 marks

do not accept acidified with sulfuric

acid (still allow result mark if correct)

allow solution of barium ions / salt not barium solution

do not accept barium hydroxide1

5

(white) precipitate / solid

do not accept incorrect colour for precipitate

allow barium sulfate (formed)

ignore ‘it goes white / cloudy’1

(b) (white) precipitate / solid

allow aluminium hydroxide (formed)

do not allow incorrect colour for precipitate1

(precipitate) dissolves (in excess)

allow sodium aluminate (formed)

allow goes clear / colourless

if incorrect colour precipitate then allow dissolves (in excess)1


(c) any two from:

apply list principle

• yellow = sodium (alum)

allow orange or yellow orange

• lilac = potassium (alum)

allow purple

• colourless = ammonium (alum)

if no colours given, allow ‘different coloured flames’ for 1 mark2

[6]

(a) (i) hydrochloric acid / HCl

accept any (named) acid1

carbon dioxide / CO2

accept bubbles / fizz / gas or limewater gets milky

ignore ‘add limewater’

do not accept other named gases

2nd mark dependant on first mark

accept for this answer only heat gives CO2 / limewater milky = 1mark

1

6

(ii) (white) precipitate / solid

ignore names of substances even if incorrect

accept white deposit / substance

do not accept any coloured precipitate1

(iii) eg flame colour of (Na) and flame colour of (K)interfere / mask / mix with each other

accept ‘can’t see the colours’ or ‘difficult to determine the colour’ or‘both produce different colours’ or a correct statement of colours orhard to distinguish

1

(b) (i) eg essential (mineral) or everyoneneeds it / some (salt) or problemswith health if have no salt

accept preservative / flavouring / taste

it = salt

(all) foods contain / use it / sodium chloride / salt1


(ii)

mark positively ie no list principle

advantages

any two from:

ignore economic arguments throughout or people eat less salt

• more people will be healthier

• (should have) less heart disease

• (should have) less cancer

• (more people with) lower blood pressure2

disadvantages

any one from:

ignore references to too much / too little (salt)

• not everyone affected

• not enough evidence

• does not provide choice

• undemocratic

• less taste / flavour

ignore no flavour / taste

• shorter shelf life / not preserved (as long)

ignore references to sell by dates

• too much potassium chloride might be bad1

[8]

(a) (i) red / brick-red / orange-red / red-orange

allow red-brown or brown-red

do not accept orange alone eg ‘red or orange’ = 01

7

(ii) sodium

allow sodium compounds

ignore incorrect symbol

or Na / Na+

if symbol alone given do not accept Na2+ or Na–

1


(iii) any one from

• accurate / sensitive

• use small amounts

• fast / quick / rapid

• ease of automation

• reliable / efficient

• operatives do not need chemical skills

ignore cost / safety / human error or ease of use or shows all theelements

1

(iv) (atomic absorption) spectroscopy or (mass) spectrometry

accept AAS / aas or mass specaccept atomic absorptionignore ms / MSdo not allow UV / IR / NMR / chromatography / GLC

1


(b) any three from:

• (safe because) similar to mothers. milk

allow calcium carbonate is in breast milkallow some mothers unable to breast feedignore ‘recommended’ alone

• babies (in developing world) would die

accept causes malnutrition

• if banned there would be a cost involved

allow it is free

• it is not a pollutant / harmful / dangerous

accept not all chemicals are pollutants / harmful / dangerous

• not mass medication

• not just used for gravestones

allow it has many usesignore only small amounts of it or it occurs naturally

• (calcium carbonate) is needed for bones / teeth / health

allow ‘essential mineral’

• Mrs Right has a personal interest or not impartial or distortsinformation / bias or she is paid by a charity

accept ‘it is (only) her opinion’3

[7]

(a) kills bacteria / sterilises (water)

allow kills microorganisms / microbes / germs

allow ‘makes (water) safe (to drink)’ or disinfectant

ignore cleans water or removes impurities / bacteria1

8

(b) goes colourless / decolourised (from red / red-brown / brown / yellow / orange)

allow colour disappears

ignore ‘goes clear’ or discoloured

do not accept incorrect initial colour

do not accept precipitate1

(c) (i) Br2 and 2Cl–

allow multiples / fractions if whole equation balanced1


(ii) changes to red / red-brown / brown / yellow / orange

do not accept effervescence / fizzing / precipitate / gas given off

ignore vapour / temperature changes / ignore initial colour1

(d) (i) 7 outer electrons or

same number of outer electrons

allow last / final shell for outerallow energy level / orbit / ring for shellallow ‘need to gain 1 e – to have a full outer shell’ignore ‘similar number of outer electrons’

1

(ii) bromine / it (atom) is bigger or

must be a comparison

outer electrons (level / shell) further from nucleus or more shells

do not accept more outer shellsignore more electrons

forces / attractions are weaker or more shielding or attracts less

do not accept magnetic / gravitational / intermolecular forcesallow ‘electron(s) attracted less easily’

electron(s) gained less easily

“outer / last / final” must be mentioned once, otherwise max 2marks.accept converse for chlorine throughout where clearly stated

3

(e) (i) white precipitate or white solid

ignore names of chemicals1

(ii) cream precipitate or cream solid

allow pale yellow / off-white precipitate / solidignore names of chemicals

1

[10]

(a) sodium carbonate / sodium hydrogencarbonate / sodium bicarbonate

Na2CO3 / NaHCO3

iesodium / sodium ions (1 mark)carbonate / carbonate ions(1 mark)incorrect formula including Na andCO3 = 1 mark

2

9


(b) calcium chloride

CaCl2ie calcium / calcium ions (1 mark) chloride / chloride ions (1 mark)incorrect formula including Ca and Cl = 1 mark

2

(c) iron or iron(II) ions

Fe2+ ferrous ionsignore anionsignore nickel / chromium

do not accept iron(III) or ferric ions51

[5]

(a) water level above the start lineandstart line drawn in ink

allow water level too high1

10

water levelfood colours would dissolve into waterorstart linethe ink would ‘run’ on the paper

1

(b) (distance moved by A) 2.8cm and 8.2 cm (distance moved by solvent)

allow values in range 2.7 − 2.9 cm and 8.1 − 8.3 cm1

1

0.34

allow 0.33 or 0.35

allow ecf from incorrect measurement to final answer for 2 marks ifgiven to 2 significant figures

accept 0.34 without working shown for 3 marks1

(c) 6.6 cm

allow values between 6.48 and 6.64 cm1

(d) solvent moves through paper1

different dyes have different solubilities in solvent1


and different attractions for the paper1

and so are carried different distances1

(e) calcium ions

allow Ca2+

1

sodium ions

allow Na+

1

(f) two different coloursorCa2+ / one is orange-red and Na+ / the other is yellow

allow brick red for Ca2+ and / or orange for Na+

allow incorrect colours if consistent with answer to 7.51

(so) colours mixor(so) one colour masks the other

1

(g) (Student A was incorrect)because sodium compounds are white not green

orbecause sodium carbonate is soluble

1

so can’t contain sodium ions1

(Student B was incorrect)because adding acid to carbonate produces carbon dioxide

1

so must contain carbonate not chloride ions1

[18]

(a) X:Fe2+ / iron(II), SO4

2- / sulfate

allow iron(II) sulfateor FeSO4

1

11

Y:Na+ / sodium, I- / iodide

allow sodium iodideor NaI

1


Z:Fe3+ / iron(III), Br- / bromide

allow iron(III) bromideor FeBr3

correct identification of any two ions = one mark

correct identification of any four ions = two marks1

(b) any five from:

allow converse arguments

method 1

• weighing is accurate• not all barium sulfate may be precipitated• precipitate may be lost• precipitate may not be dry• takes longer• requires energy

allow not all the barium hydroxide has reacted

method 2• accurate• works for low concentrations

allow reliable / precise5

[8]

(a) (i) ionic (bonding)112

(ii) ions cannot move in solid or are in fixed positions

do not accept electrons / atoms / molecules

ignore particles

must mention ions1

but can move in solution1

(b) silver chloride formed1

which is insoluble1

(c) (i) aluminium1

calcium

accept other metal ions that also give white precipitates (such aslead and zinc)

1


(ii) add excess sodium hydroxide solution

the second mark of each pair is dependent on the first mark beingawarded.

1

precipitate remains1

carry out a flame test1

not red / orange

accept any colour that is not orange / red

give full credit for answers that correctly eliminate other cations in(c)(i) that would give white precipitates with a few drops of NaOH

1

[11]


Marks awarded for this answer will be determined by the Quality of Communication (QC) as wellas the standard of the scientific response. Examiners should also apply a ‘best-fit’ approach tothe marking.

0 marksNo relevant content

Level 1 (1 – 2 marks)Any description of a method used and / or a result given

Level 2 (3 – 4 marks)Description of workable methods used, with results to identify positive or negative ions

Level 3 (5 – 6 marks)Description of methods used to identify both positive and negative ions, with relevantresults

examples of the points made in the response

extra information

Test: add (platinum / nichrome) wire (for the flame test)

accept any method of introducing the solution into the flame, eg asplint soaked in the solution or sprayed from a bottle

Result: the sodium compounds result in a yellow / orange / gold flame or the potassiumcompound results in a lilac / purple / mauve flame

student could state that potassium carbonate gives a differentcolour to the three sodium compounds as long as it is clear that theflame test colour comes from Na+ or K+

Test: add dilute nitric acid to all four solutions

allow any acid

Result: sodium carbonate and potassium carbonate will effervesce or sodium chloride andsodium iodide will not effervesce

Test: add dilute nitric acid followed by silver nitrate

Result: sodium chloride and sodium iodide produce a precipitate or sodium chlorideproduces a white precipitate and sodium iodide produces a yellow precipitate

accept sodium carbonate and potassium carbonate do not producea precipitate

[6]

13


(a) lithium

allow Li+ / Li1

yellow

allow orange1

(b) silver nitrate (solution)

incorrect test = 0 marks

ignore (nitric) acid

do not allow other named acids1

white precipitate1

(c) blue precipitate (with sodium hydroxide) indicates copper ions

allow Cu2+

1

and white precipitate (with barium chloride) indicates sulfate ions

allow SO42-

accept compound X is copper sulfate / CuSO4 for 1 mark1

but iron(II) ions produce a green precipitate (with sodium hydroxide)1

[7]

14

(a) (i) Na2CO3: HCl → gas / effervescence / bubbles (1) CO2 / carbon dioxide / turns lime water milky (1)

1

15

NaCl: AgNO3 → white ppt (1) silver chloride (1)

1

NaNO3: Al + NaOH → pungent / sharp smell / choking gas (1) NH3 / ammonia / turns (red) litmus blue(1)

1

Na2SO4: BaCl2 → white ppt (1) barium sulfate (1)

1

each correct test and one result = 1 mark

one other result for any test = 1 mark this mark can only beawarded once


(ii) all would give a yellow / yellow-orange (flame) / same coloured (flame) / sameresults

allow orange (flame) 1

or

they all contain sodium1

(b) any two from:

ignore cost/errors

• fast / quick or comment about speed

allow precise

• small amounts/sensitive

allow can be left to run/continuous analysis

• accurate


accept operators do not need chemical skills

• sample not used up

• reliable / efficient2

[7]

(a) (i) place sample in flame

accept flame test

accept any workable method

allow burn

ignore heat1

16

sodium: yellow (flame)

allow orange1

potassium: lilac (flame)

allow purple1

(ii) (lilac) colour (of potassium) obscured by (yellow) colour of sodium

allow difficult to see two colours

allow sodium colour is brighter

allow colours mix1


(b) acidify (with nitric acid)

do not accept if acidified with anything other than nitric acid1

add silver nitrate (solution)1

white precipitate

depends on second marking pointallow white solid

ignore silver chloride

ignore solution goes cloudy / milky1

(c) (i) add excess (sodium hydroxide)

allow add sodium hydroxide1

aluminium (ions / hydroxide (re)dissolve

depends on first marking pointallow if aluminium, (white) precipitate / solid dissolvesallow magnesium (ions / hydroxide) do not (re)dissolve

1

(ii) place sample in flame

accept flame test

accept any workable methodallow burn

ignore heat1

flame does not go red

accept calcium (ions / hydroxide would produce) red flame

allow magnesium (ions / hydroxide) (produce) no flame colour1

[11]

(a) (i) (bubble gas produced through) limewater

incorrect tests = zero1

17

(limewater) goes cloudy / milky1

(ii) ignore yes or no

red flame indicates that calcium / lithium ions present

allow aluminium has no flame colour

or

Ca/Mg also produce a (white) precipitate with NaOH1


the (white) precipitate formed in test 3 or by adding sodium hydroxidesolution would dissolve (in excess) if aluminium ions were present

1

(iii) ignore yes or no

because a white precipitate is formed in test 4 or by adding silver nitrate1

but chloride ions are in hydrochloric acid1

(b) (i) mass spectrometry

allow MS

or

atomic absorption spectroscopy

allow AAS

spectrometry / spectroscopy alone is insufficient1

(ii) can detect a small(er) amount of the substance

allow can detect small(er) changes

allow small(er) sample sizes

ignore references to precision / accuracy1

[8]

(a) (i) incorrect test or no test = 0 mark

testing the solution or using blue litmus = 0 mark

(test ammonia / gas with red) litmus

accept any acid-base indicator with correct result1

18

(goes) blue

OR

(conc.) HCl (1)

white fumes / smoke / solid (1)

allow white gas / vapour

OR

(test ammonia / gas with) Universal Indicator (1)

blue / purple (1)1


(ii) incorrect test or no test = 0 marks

add barium chloride / BaCl2 (solution)

do not accept H2SO4 added

or add barium nitrate / Ba(NO3)2 (solution)

allow Ba2+ solution / aqueous added1

white precipitate / solid (formed)

allow white barium sulfate / BaSO4

ignore barium sulfate / BaSO4 alone1

(b) (i) fully / completely ionised / dissociatedor hydrogen ions fully dissociated

accept has more ions than weaker acid / alkali of sameconcentration

ignore strongly ionised

do not accept ions are fully ionised

ignore concentrated or reference to concentrations of ions1

(ii) methyl orange

accept correct spelling only

accept any strong acid-weak base indicator

do not allow phenolphthalein / litmus / universal indicator1

(iii) 32 × 0.05/1000 or 0.0016 (mole H2SO4 )

accept (0.05 x 32) = (V x 25) or 0.05 x 32 / 251

(reacts with) 2 × 0.0016 or 0.0032 (mole NH3 in 25 cm3)

accept dividing rhs by 2 or multiplying lhs by 21

(0.0032 × 1000/25 =) 0.128

allow ecf from previous stage

correct answer 0.128 or 0.13 with or without working gains all 3marks

1


(iv) 2.176 or 2.18

correct answer with or without working

or ecf from candidate’s answer to (b)(iii)

or 2.55 if 0.15 moles used

if answer incorrect or no answer

0.128 × 17 or 0.13 x 17

or their (b)(iii) × 17

or 0.15 × 17 gains 1 mark2

[11]

(a) (i) each correct test and one result = 1 mark

one other result for any test = 1 markthis mark can only be awarded once

1

Na2CO3: HCl → (odourless) gas (1) CO2 / carbon dioxide (1)

1

NaCl: AgNO3 → white ppt (1) silver chloride (1)

1

NaNO3: Al + NaOH → pungent /sharp smell / choking gas (1) NH3 / ammonia (1)

1

Na2SO4: BaCl2 → white ppt (1) barium sulphate (1)

1

19

(ii) all would give a yellow / yellow-orange(flame) / same coloured (flame) / same results

allow orange (flame)

or

they all contain sodium owtte1


(b) any two from:

ignore cost

• fast / quick or comment about speed

ignore human error

• small amounts

accept any valid answer

• sensitive / accurate

accept operators do not need chemical skills


• sample not used up

• reliable / efficient

• can be left to run / continuous analysis

ignore results can be saved2


C8 IDENTIFICATION OF IONS BY Name: CHEMICAL AND … · 2018-03-29 · This question is about...

Documents

Transcript of C8 IDENTIFICATION OF IONS BY Name: CHEMICAL AND … · 2018-03-29 · This question is about...