1G R A V I M E T R I C A N A L Y S I S

MATER IALS

Invest igat ion

(per student or group)- 100 g wet beach sand or soil from high salinity area- filter funnel- filter paper- glass rod- 250 mL beaker- large evaporating basin- drying oven or electric hot plate- Bunsen burner and heatproof mat- tripod and gauze- balance (accurate to 0.01 g)- 100 mL measuring cylinder- retort stand with ring clamp

MATER IALS

1Invest igat ion

Gravimetric analysis

� SyllabusIdentify data sources, plan, choose equipmentand perform a first-hand investigation toseparate the components of a naturallyoccurring or appropriate mixture such as sand,salt and water, and gather first-hand informationby carrying out a gravimetric analysis of themixture to estimate its percentage composition.

Introduction

In this investigation you will plan your own investigation in order todetermine the percentage of water and the percentage of soluble salts ina sample of sand or soil.

On completion of this investigation, you will be able to:● select and assemble appropriate equipment● perform an investigation safely according to your plan● recognise the practical applications of gravimetric analysis● identify various procedures for the separation of mixtures ● report your findings in an acceptable, scientific way.

Procedure

1 Search the literature using the library or the Internet to find outabout gravimetric analysis.

2 Plan an investigation to separate water and soluble salts from yoursample of sand or soil. Assess all the possible risks associated with yourchosen procedure.

3 Choose and set up your equipment.4 Perform the gravimetric analysis and collect all the data necessary to

calculate the percentage of water and soluble salts present in yoursample.

5 Record your data and observations.6 Write a report of your investigation. Your report must include the

following headings:● Purpose—brief outline of what your investigation aims to achieve.● Procedure—step-by-step outline and diagrams of the equipment

used to collect your data; also include references to any sourcesused.

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2 G R A V I M E T R I C A N A L Y S I S

� Disposal of wasteAll solids should bedisposed of by wrappingin paper and placing inthe garbage bin. Allliquids can be washeddown the sink. Avoidspilling sand or soil in the sink.

Discussion

1 What was the basis of separation of the soluble salt from the insolublecomponent in your sample?

2 Is the salt you have isolated a pure substance or a mixture? Explainyour answer.

3 Describe two situations where gravimetric analysis can supply usefuldata for chemists and other scientists (such as geologists).

4 Give one practical application from industry where the followingseparation techniques are applied:a sievingb sedimentationc evaporationd distillatione fractional distillation.

● Results—table of data collected and observations made, as shownin the examples in Tables 1 and 2.

● Calculations—percentage composition of your sample.● Conclusion—this must answer the purpose.● Discussion—answer the questions below.

R E S U LT S

TABLE 2

TABLE 1

Material Observations

sample of sand

sand without water

soluble salts

Item Mass (to nearest 0.01 g)

empty beaker

beaker and wet sand

beaker and dry sand

empty evaporating basin

mass of basin and salt

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3G R A V I M E T R I C A N A L Y S I S

The iron ore that is richest in iron is magnetite (Fe3O4).

a Calculate the percentage of iron in this ore.

b How many kilograms of pure iron could you theoretically obtain from 1 tonne of magnetite?

FOLLOW- UP

5 A team of geologists has found a possible iron ore source, whichhappens to be magnetic. They have analysed a 1 kg sample of ore as follows:

The sample was crushed and passed over a magnetic belt toseparate magnetite from the non-magnetic residue. An amount of345 g magnetic ore was obtained. The non-magnetic residue wasplaced in a tank and underwent froth flotation. The lighter, copper-containing material floated while the heavier, silicon-containingmaterial sank. 152 g copper ore was extracted.

Calculate the percentage composition of the original sample, withrespect to iron ore and copper ore.

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4 I N V E S T I G A T I O N O F P H Y S I C A L P R O P E R T I E S O F A R A N G E O F E L E M E N T S

Invest igat ion

Please indicate by signing that you have understood the information in the safety table.

Name (print):

I understand the safety information (signature):

Stations 1 & 2(for teacher demonstration)- 1 L liquid nitrogen in Dewar flask- banana- soft wooden board- nail- leaves, flowers- rubber tubing- sodium- scalpel and forceps- 250 mL beaker with watch-glass cover- phenolphthalein- filter paper

Stations 3 & 4(per student or group)- DC source- 3 electrical leads, 2 with crocodile clips at one end- ammeter or multimeter- petri dish- 3 strips each of aluminium, zinc, tin, lead, magnesium- 3 pieces of copper wire- 2 graphite rods- powdered carbon- amorphous sulfur (2 petri dishes with 1 g chunk in each)- iodine (2 covered petri dishes with 0.5 g in each)- small hammer and anvil- red phosphorus- 4 iron nails

MATER IALS

2Invest igat ion

Investigation of physical properties of a range of elements

Material used Hazard Control

lead metal Lead salts are highly toxic Wash hands with soap and water after polishing metal

iodine Toxic by all routes of exposure, Wear safety glasses and gloves stains skin and clothing, vapour highly irritating to lungs

red phosphorus Toxic if ingested Wear safety glasses and gloves

Pre-lab safety information

INVESTIGATION 2: Investigation of physical properties of a range of elements

� SyllabusPlan and perform an investigation to examinesome physical properties, including malleability,hardness and electrical conductivity, and someuses of a range of common elements to presentinformation about the classification of elementsas metals, non-metals or semi-metals.

Introduction

Very few elements found in nature are pure. Most pure elements areinvisible gases. Solid elements are mainly extracted from theircompounds.

You will investigate a range of common elements and use theirphysical properties to classify them as metals or non-metals.

On completion of this investigation, you will be able to:● list physical properties that are common to all metals● distinguish the physical properties of non-metals● recognise the uses of a range of common elements● position metals in the appropriate section of the Periodic Table.

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5I N V E S T I G A T I O N O F P H Y S I C A L P R O P E R T I E S O F A R A N G E O F E L E M E N T S

� Disposal of wasteAll solids can be wrappedin paper and disposed ofin the garbage bin. Keepany elements that couldbe reused.

TABLE 1R E S U LT S

Test Observation before cooling Observation after cooling

test-tube with air

banana

leaves

flowers

rubber tubing

Station 1: LIQUID NITROGEN (TEACHER DEMONSTRATION)

1 Your teacher will immerse in the liquid nitrogen a test-tube (containingair) suspended from the retort stand.

2 Your teacher will immerse a banana in the liquid nitrogen. The bananacan then be used to hammer a nail into the wooden board.

3 Your teacher will immerse leaves and flowers in the liquid nitrogen.4 Your teacher will demonstrate the effect of cooling on the flexibility

of rubber tubing.

Discussion

1 At what temperature does nitrogen liquefy?2 What is the main source of nitrogen on Earth? What percentage of

this nitrogen is found as a gas?3 a What effects does liquid nitrogen have on plants such as bananas,

flowers and leaves?b How could these effects be used in an industrial application?

4 a What was the result of cooling the test-tube, containing air, inliquid nitrogen?

b Give one industrial application of this observation.

Station 2: SODIUM METAL (TEACHER DEMONSTRATION)

1 Your teacher will take a piece of sodium out of paraffin oil, wipe itwith filter paper and test the sample for electrical conductivity.

2 Your teacher will cut a small piece of sodium (about 3 mm3), drop itinto a half-filled 250 mL beaker of water and cover the beaker with awatch-glass.

3 When the reaction stops, your teacher will add a few drops ofphenolphthalein.

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6 I N V E S T I G A T I O N O F P H Y S I C A L P R O P E R T I E S O F A R A N G E O F E L E M E N T S

TABLE 2R E S U LT S

Test Observation

sodium in oil

sodium (cut)

conductivity test

reaction with water

phenolphthalein added

Discussion

1 Does sodium look like a typical metal?2 Why is sodium kept under oil?3 Name two physical properties that would indicate that sodium is a metal.4 List at least five different observations you made when sodium reacted

with water.5 Write a word equation that is consistent with your observation of

sodium reacting with water.6 Explain why the indicator changed colour during the reaction of

sodium with water.7 On Earth, where would you find sources from which sodium could

be extracted?8 Name one chemical that contains sodium. What is its use?

Station 3: LUSTRE, DUCTILITY, MALLEABILITY AND HARDNESSOF SOLID ELEMENTS

1 Plan an investigation to rank given metals for their: a lustre (reflection of light, shininess, dullness, silver or gold colour)b ductility (if metal can be drawn out into a wire)c malleability (if metal is able to be hammered into sheets)d hardness (soft or hard, brittle or flexible)

2 Record your observations in Table 3.

TABLE 3R E S U LT S

Element Lustre and shape Hardness Malleable Ductileyes/no yes/no

aluminium

zinc

iron

copper

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7I N V E S T I G A T I O N O F P H Y S I C A L P R O P E R T I E S O F A R A N G E O F E L E M E N T S

Discussion

1 Rank the above elements according to:a descending order of lustreb increasing order of hardnessc increasing order of malleability.

2 Name the most ductile element and its industrial use.3 Name an industrial use for:

a aluminiumb iron.

FIGURE 1 Conductivity tester

DC ammeter

petri dishelement to be tested

crocodile clips

Station 4: CONDUCTIVITY OF ELEMENTS

1 Set up the conductivity tester, as in Figure 1.2 Set up a DC source to deliver 2 V. Place a piece of the element to be

tested on a watch-glass or petri dish. Touch the ends of the elementwith the crocodile clips (attached to leads). Observe the movement ofthe ammeter needle.

3 Repeat the test with each element, both lumps and powders.4 Record your observations in Table 4.

tin

lead

magnesium

graphite rod (carbon)

sulfur

iodine Do not test Do not test

red phosphorus Do not test Do not test

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FOLLOW- UP

8 I N V E S T I G A T I O N O F P H Y S I C A L P R O P E R T I E S O F A R A N G E O F E L E M E N T S

Identify the five most abundant (by weight) elements in the biosphere, the lithosphere, thehydrosphere and the atmosphere. Describe the most common physical and chemical forms in whichthey are found. Tabulate your answers.

TABLE 4R E S U LT S

Element Current (amps)

aluminium

zinc

iron

copper

tin

lead

magnesium

graphite rod (carbon)

powdered carbon

sulfur

iodine

red phosphorus

Discussion

1 List the common properties of the elements that conducted electricity.2 Is there an element that conducted electricity, but has other

properties that are different from the other conductors?3 List the common properties of those elements that did not conduct

electricity.4 Classify all the elements in this investigation into two distinct classes,

leaving those that cannot be clearly classified as ‘undecided’.5 In what general area of the Periodic Table will you find:

a metals c semi-metalsb non-metals d gaseous elements?

6 Name the liquid elements.

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9

MATER IALS

Invest igat ion

Please indicate by signing that you have understood the information in the safety table.

Name (print):

I understand the safety information (signature):

(per student or group)- 1 g calcium carbonate (powdered)- 1 g sodium carbonate (anhydrous)- 1 g copper(II) carbonate- 1 g nickel carbonate- 40 mL limewater- 9 test-tubes- 4 delivery tubes with stoppers- 4 spatulas or teaspoons- Bunsen burner and heatproof mat- test-tube holders

MATER IALS

3Invest igat ion

Decomposition of carbonates

Material used Hazard Control

sodium carbonate Slightly toxic if ingested Wear safety glasses

copper carbonate Slightly toxic if ingested Wear safety glassesand by skin contact Wash hands after use

nickel carbonate Toxic if ingested Wear safety glasses May cause allergic reaction, Wash hands after use teratogen (pregnant females to avoid)

limewater Slightly toxic if ingested Wash hands after use

Pre-lab safety information

INVESTIGATION 3: Decomposition of carbonates

� SyllabusPlan and safely perform a first-handinvestigation to show the decompositionof a carbonate by heat, using appropriatetests to identify carbon dioxide and theoxide as the products of the reactions.

Introduction

Decomposition of compounds by heat is common practice in manyindustries. In this investigation, you will decompose a variety ofcarbonates to compare the strength of the bonds in these compounds.

On completion of this investigation, you will be able to:● recognise that heat energy can cause a chemical change● identify the products of decomposition ● demonstrate the difference between physical and chemical change● relate decomposition to the strength of bonds between atoms.

D E C O M P O S I T I O N O F C A R B O N A T E S

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10 D E C O M P O S I T I O N O F C A R B O N A T E S

Procedure

1 Add about 0.5 g (one spatula-full or half a teaspoon) of the first car-bonate to a clean, dry test-tube. Insert a stopper with delivery tube.

2 To another test-tube add about 10 mL clear limewater.3 Set up the apparatus as shown in Figure 1.

test-tube holder

glass tube

rubber tubing

limewater

carbonate

Bunsen burner

FIGURE 1 Experimental set-up

� Disposal of wasteAll solids can bedisposed of in thegarbage bin, and liquidswashed down the sink.

4 Gradually warm the test-tube containing the carbonate. Then heatthe test-tube strongly over the clear Bunsen flame and observe thechanges in the limewater.

5 Stop heating as soon as you observe changes. If changes are notobserved after 5 minutes, stop heating.

6 Record your observations in the results table below.7 Repeat with the other carbonates. When you are finished, leave the

test-tubes to cool in the rack.8 Plan and safely perform an investigation of solubility of these four

carbonates in water. (Hint: take only a small amount of each solid, thesize of a rice grain.)

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FOLLOW- UP

11D E C O M P O S I T I O N O F C A R B O N A T E S

TABLE 1R E S U LT S

Carbonate Effect of heat on solid Effect on limewater Solubility in water

calcium carbonate

sodium carbonate

copper carbonate

nickel carbonate

Discussion

1 Was heat energy absorbed or released during each decomposition?2 On a molecular level, explain what happened to the carbonate when

heated.3 Write balanced equations for the decomposition reactions you

observed, and indicate whether energy was released or absorbed byplacing E on the appropriate side of the equation.

4 Explain why some carbonates easily decomposed and others did not.5 Give evidence from your investigation that carbon dioxide gas was

produced, and that an oxide was formed.6 Write a balanced equation for the observation with limewater

(Ca(OH)2(aq)).7 On a molecular level, explain what process is involved when a carbonate

dissolves.8 Why did some carbonates easily dissolve on heating, but did not

decompose?

Decomposition of carbonates is common in many industries. Find out:

a What is the natural raw material for the cement industry?

b What processes are involved in the manufacture of cement?

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12 E F F E C T O F L I G H T A N D E L E C T R I C I T Y O N A C O M P O U N D

Invest igat ion

Please indicate by signing that you have understood the information in the safety table.

Name (print):

I understand the safety information (signature):

(per student or group)- 0.5 g silver carbonate- 0.5 g silver nitrate- 0.5 g silver sulfate- 0.5 g silver chloride- 100 mL 0.1 M sulfuric acid- 4 petri dishes- sunlight, spotlight, overheadprojector or similar light source- voltameter or similar apparatus- 12 V DC source- 2 test-tubes- taper and splint- molecular model kit

MATER IALS

4Invest igat ion

Effect of light and electricity on a compound

Material used Hazard Control

silver carbonate Toxic if ingested, stains skin black Wear eye and skin protection

silver nitrate Toxic if ingested, corrosive to skin and eyes, Do not touch, wear eye and stains skin black skin protection

silver sulfate Harmful by inhalation and if swallowed Wear eye and skin protection Irritating to the eyes and skin

Pre-lab safety information

INVESTIGATION 4: Effect of light and electricity on a compound

� SyllabusGather information using first-hand sources toobserve the effect of light on silver salts andidentify an application of the use of thisreaction. Observe the electrolysis of water,analyse the information provided as evidencethat water is a compound and identify anapplication of the use of this reaction.

Introduction

Conversion of energy to other forms of energy is an everyday occurrence.In this investigation you will investigate the effect of light energy on silversalts, and the conversion of electrical energy to chemical energy.

On completion of this investigation, you will be able to:● recognise the effect of light energy on compounds● identify an application of decomposition of silver salts● use models to explain what is happening when water boils● trace movements of atoms and ions during electrolysis of water.

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13E F F E C T O F L I G H T A N D E L E C T R I C I T Y O N A C O M P O U N D

� Disposal of wasteDo not dispose ofanything. Cover allpetri dishes and returnthem to your teacher.

TABLE 1R E S U LT S

Salt Immediate observation Effect of light

silver nitrate

silver chloride

silver carbonate

silver sulfate

Procedure A: EFFECT OF LIGHT ON SILVER SALTS

1 Position the petri dishes containing 0.5 g silver salts under the lightsource.

2 Remove the cover and leave them exposed until a change of colour isobserved.

3 Record your observations in Table 1.4 When all observations are completed and recorded in the table, see if

any further colour change has occurred. If so, note this further change.

Discussion

1 From your observations, what energy conversion has taken place?2 On a molecular level, what is happening to the silver salt when it is

exposed to light?3 Account for the colour change of silver chloride and silver carbonate

and write the balanced equation for their decomposition.4 Are the above reactions exothermic or endothermic?5 What are the practical applications of the above reactions?6 Give formulae for the other two silver salts tested.

Procedure B: ELECTROLYSIS OF WATER(TEACHER DEMONSTRATION)

1 Set up a voltameter or equivalent apparatus, as shown in Figure 1. Fill itwith sulfuric acid. Connect electrodes to a 4 V DC supply and continueelectrolysis until one of the tubes above the electrode is full of gas.

2 Measure the length of gas collected above each electrode and recordthe polarity of each electrode. Record the results in Table 2.

3 Collect the gas from the voltameter by placing a clean, dry test-tubeover one of its taps. Close the tap.

4 Test the gas at the negative electrode with a lighted taper. Test theother gas with a glowing splint.

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