TOPIC

Mde Concepts

1.

E Multiple Choice Questions

Which of the following is not equivalent to 0.250 moles of pure water?

A. 0.0045 kg

B. 6.00 dm3

C. 1.50 x 1023 molecules

D. 4.50 x 1023 atoms

) When solid sodium hydrogen carbonate is heated in a beaker to above 70 'C, it thermally decomposes

into solid sodium carbonate, water and carbon dioxide based on the equation:

2NaHCO., +NarCO. + HrO + CO,

What is the loss in mass when 50.4 g of solid sodium hydrogen carbonate is heated?

A. 50.4 g

B. 31.8 g

C. 18.6 g

D. t3.2 s

3. Dilute acids react with most metals to produce a metal salt and hydrogen gas. When 0.006 moles of metal

W was added to an excess of a dilute acid, 144 cm3 of hydrogen was evolved. Which of the following

shows the correct equation for the reaction?

A. 2W +2H. -+2W* +H,B. 2W + 6H. -+ 2w3* + 3H2

C. W + 4H* -+W4* +2H,D. W+2H*-+W2*+H,

4. Aqueous sodium hydroxide reacts with the solution of a certain metal chloride MC/. to form a precipitate

of the metal hydroxide according to the equation:

MC/, + xNaOH -+ M(OH), + xNaC/

10.0 cm3 of 6.00 mol/dm3 NaOH solution was used to react exactly with 10.0 cm3 of 3.00 mol/dm3

MC/. solution. What is the formula of the metal chloride?

A. MC/B. MC/2

c. MC/3

D. M2Cl

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A solution of dibasic acid with a concentrationof 14.4 gldm3 is titrated with a solution of sodium hydroxidewith a concentration of 0.200 mol/dm3. It is found that exactly 30.0 cm3 of sodium hydroxide solutionneutralises 25.0 cm3 of the acid. What is the relative molecular mass of the acid?

A. 60.0

B. 72.O

c. 120.0

D. 240.0

6. 37.5 g of hydrated copper (II) sulfate, CuSO,,.5H,O, is dissolved in water and the solution made up to1.00 dm3. What is the concentration of the solution with respect to the sulfate ion?

A. 0.050 mol/dm3

B. 0.100 mol/dm3

C. 0.150 mol/dm3

D. 0.230 moVdm3

7. 1.97 g of an unknown metal carbonate, MCO, reacts completely with 50.0 cm3 of 0.400 mol/dm3

hydrochloric acid. What is the relative atomic mass of M?A. 38.5

B. 98.5

c. 137.0

D. 191.0

8. A compound contains 52 Vo carbon, 13 Tohydrogen and 35 Eo oxygel by mass. What is a possible formulaof the compound?

A. CH3COOH

B. CH3OH

C. HCOOH

D. C2H.OH

9. In an experiment conducted at room temperature and pressure, 5.00 cm3 of gaseous hydrocarbon reacted

with excess oxygen to form 30.0 cm3 of carbon dioxide and 15.0 cm3 of water vapour. What is the formulaof the hydrocarbon?

A. CHo

B. CrHo

c. C,H4

D. CuHu

10. What is the total number of moles of ions in 500 cm3 of 0.500 mol/dm3 (NHo)rCu(SOo)r(aq)?

A.

B.

C.

D.

0.25 moles

0.50 moles

0.75 moles

1.25 moles

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LL. UrO, is a catalyst, prepared by heating a uranium nitrate salt, UOr(NO,)r. This salt decomposes

quantitatively to give U3O8, NO2 and O, only. How many moles of UrO, are produced from six moles

of the salt?

A. one moleB. two moles

C. three moles

D. six moles

12. A complex mixture of calcium compounds, proteins and other substances is known to be present in

human bone. When a bone is strongly heated in a generous supply of air, the only residue left is calcium

oxide.

When a bone sample weighing 100 g is heated in air, 28.0 g of calcium oxide is obtained. What is the

percentage by mass of calcium in the sample of bone?

A. l0.O Vo

B. 2O.0Vo

C. 28.0%io

D.7l.4Vo

13. The following statements describe a 12.0 g sample of carbon- 12.

I The number of atoms in the sample is 6 x 1023.

II The number of atoms in the sample is the same as the number of atoms in 4.00 g of He-4.

m The number of atoms in the sample is the same as the number of atoms in 2.00 g of hydrogen.

Which statements are correct?

A. I and IIB. I and IIIC. II and IIID. All of the above

14. What is the concentration of the solution that is produced by mixing 40.0 cm3 of 0.200 mol/dm3 NaOH

with 60.0 cm3 of 0.100 mol/dm3 HC/?

A. 0.080 mol/dm'NaC/B. 0.150 mol/dm'NaC/C. 0.060 moVdm'NaC/ + 0.020 mol/dm3 NaOH

D. 0.020 mol/dm'NaC/ + 0.020 mol/dm3 NaOH

L5. 40.0 cm3 of aqueous 1.00 mol/dm3 solution of the hydroxide of metal X neutralises exactly 80.0 cm3 of

0.250 mol/dm' aqueous sulfuric acid. What is the formula for the sulfate of X?

A. X2SO4

B. XSO4

c. x,(so4)jD. X(SO4)'

16. When 12.0 g of magnesium ribbon reacts with excess sulfuric acid, 55.5 g of magnesium sulfate is

produced. What is the percentage yield of magnesium sulfate?

A. 55.5 Vo

B. 12.5 7o

C. 92.5 7o

D. 97.5 Vo

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E Structured Questions

1. Aspirin, also known as acetylsalicylic acid is often used as an analgesic to relieve minor aches, pains as

well as to reduce fever. Aspirin is commonly dispensed over the counter in the form of pills.(a) Determine the following:

(i) What is the molar mass of aspirin, CrHrOo?

(ii) How many moles of aspirin are there in 2.00 g of this substance?

(iii) What is the mass, in grams, of 0.866 moles of aspirin?

(iv) How many aspirin molecules are there in I .7 4 g of this substance?

(v) What is the mass, in grams, of 1.00 x 1023 molecules of aspirin?

(vi) How many carbon atoms are there in one mole of aspirin?

(b) Predict whether each of the following statements is true or false when aspirin is dissolved in a beaker

of water. Circle T or F accordingly.

(i) Blue litmus paper turns red when placed inside the beaker. T/F(ii) The solution will taste slightly sour, T IF(iii) The solution will produce a white precipitate when mixed with limewater, T/F(iv) Magnesium ribbon that is placed inside the beaker will disappear after some time. TIP(v) It will produce a gas that is able to relight a glowing splint. T IF(v) It is a poor conductor of electricity. T/r

2. (a)

(b)

(c)

(d)

(e)

A student can only recall the chemical formula of a mineral as KrA/u(SOo),(OH), but remembers

clearly that its empirical formula is KA/,SOrHr. What are the values of a and b?

What is the ratio of the number of moles of molecular chlorine to the number of moles of molecularoxygen that would result from the breakup of the compound C/rO, into its constituent elements?

Calculate the percentage yield when 31.0 g of methyl salicylate (CsHsO3) is obtained from thereaction of 50.0 g of salicylic acid with an excess amount of methanol.

The equation for the reaction is: CrHuO, + CHrOH -+ C*H.O., + HrOWhat is the percentage of the number of carbon atoms and the percentage by mass of carbon atomsin one molecule of glucose, CuH,rOu?

6.00 dm3 of a gas G, has a mass of 8.00 g at room temperature and pressure. What is the relativeatomic mass of G?

3. 8.00 g of a mixture of anhydrous sodium carbonate and sodium chloride (an impurity) was madeup to 500 cm3 of aqueous solution. 25.0 cm3 of this solution neutralised 10.0 cm3 of 0.200 mol/dm3hydrochloric acid.(a) calculate the molar concentration of sodium carbonate solution.(b) Find the mass of sodium chloride present in the mixture.

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4.

6.

Household bleach contains the active ingredient, hydrogen peroxide (HrO, solution. Its decomposition

into oxygen gas and water exhibits a strong oxidising property.

(a) Draw a dot-and-cross diagram of a molecule of hydrogen peroxide.

(b) Write a balanced chemical equation for its decomposition, with state symbols.

(c) 136 g of bleach decomposed to give 2.40 dm3 of oxygen gas. Calculate the percentage purity of

hydrogen peroxide in household bleach.

(d) Using the Collision Theory, explain the effectiveness of oxygen as a bleaching agent with increasing

temperature.

(e) If more water is added into the household bleach, will the bleach become more or less effective in

its bleaching action? Explain your answer.

People with kidney problems are advised against eating carambola fruit, commonly known as starfruit

as it contains a significant amount of oxalic acid. The concentration of oxalic acid is generally between

0.500 to 1.00 mol/dm3. The acid concentration in starfruit can be determined by performing an acid-base

titration with sodium hydroxide solution.

(Assume that the oxalic acid found in star fruit is dibasic and can be represented by HrA.)

(a) A student suggested that25.0 cm3 of the starfruit juice should be pipetted into a conical flask and

titrated against 0.100 mol/dm3 sodium hydroxide solution.

(i) Based on the information provided, calculate the maximum volume of sodium hydroxide

solution required for complete neutralisation.

(ii) Suggest why the student's procedure may not be appropriate using common laboratory

apparatus.

(b) Oxalic acid contains 26.7 Vo carbon and2.2O Vohydrogen by mass. The rest is oxygen.

(D Determine the empirical formula of oxalic acid.

(ii) The relative molecular mass of oxalic acid is 90.0. Determine the molecular formula of oxalic

acid.

(iii) A patient was advised by the doctor to consume not more than 0.05 g of oxalic acid per day. Ifa typical serving of starfruit contains 1.10 x l0r moles of oxalic acid, calculate the maximum

number of servings of starfruit the patient can eat a day.

(a) Calculate the mass of Mg(NO.), required to prepare a 250 cm3 of solution containing 0.250 moVdms

of nitrate (V) ions.

(b) How many moles of sodium ions, Nat, are present in 250 cmr of 0.400 mol/dm3 of NarSOo

solution?

An aqueous solution of NaOH contains 1.80 g of OH- ions per dm3. 20.0 cm3 of the solution reacts with

26.25 cm3 of 0.040 mol/dm3 HjPO4 solution.

(a) How many moles of NaOH react with one mole of HrPOo?

(b) Deduce the chemical equation for this reaction.

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8. 6.45 g of sodium thiosulfate pentahydrate (NarSrO.,. 5HrO) is dissolved in water and made up to 250 cm3

in a volumetric flask.

(a) Determine the concentration in g/dm3 of thiosulfate ions in the solution.

40 cm3 of the solution is removed and made up to 250 cm3 in another volumetric flask.

(b) What is the concentration in g/dm3 of thiosulfate ions in the new solution?

9. Solution A contains 4.00 g of NaOH per dm3. Solution B contains H2SO4. In an experiment, 25.0 cm3 ofsolution B reacted with 18.0 cm3 of solution A.

Calculate

(a) the concentration of B in moles per dm3,

(b) the concentration of B in grams per dm3, and

(c) the number of grams of SOo2- ions in 1.00 dmr of solution B.

(M,: H, 1.00; O, 16.0; Na, 23.0; S, 32.0)

10. (a) A sample containing ammonium sulfate was warmed with 250 cmt of 0.800 mol/dm3 sodium

hydroxide solution. After the evolution of ammonia had ceased, the excess sodium hydroxide

solution was neutralised by 85.0 cm3 of 0.500 mol/dm3 hydrochloric acid. What is the mass ofammonium sulfate in the sample?

(b) 4.30 g of an impure sample of ammonium chloride was warmed with 100 cm3 of 1.00 mol/dm3

sodium hydroxide solution. The mixture was boiled until all the ammonia was driven off. The excess

sodium hydroxide in the mixture required 50.0 cm3 of 0.250 mol/dmr sulfuric acid to be neutralised.

Calculate the percentage purity of the ammonium chloride sample.

11. A chemist mixed 25.0 cm3 of 0.100 mot/dm' HrSOo with 25.0 cm3 of 0.100 mol/dm'HCl.25.O cm3 of0.200 mol/dm'KOH was then added to the mixture.

Which of the following volumes of 0.050 mol/dm3 NaOH will cause the mixture to become alkaline?

Explain your answer with calculations clearly shown.

I 50.0 cm3

II 60.0 cm3

m 70.0 cm3

12. A chloride of an unknown transition metal Z has the formula ZCI.. 32.5 g of ZCl, solid was added to

water to form an aqueous solution of ZClr. It was found that 300 cmr of 2.00 mol/dm3 aqueous silver

nitrate was required to precipitate all the chloride ions.

(a) Determine the relative atomic mass of metal Z.

(b) Identify metalZ.

13. 75.0 cm3 of 0.200 moVdm3 sodium hydroxide was added to25.0 cm3 of 0.200 mol/dm3 sulfuric acid.

What was the concentration of excess sodium hydroxide in the resultant solution?

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14, The following equation represents the precipitation reaction between lead (II) nitrate solution and

potassium iodide solution.

aPb(NO,)r(aq) + bKl(aq) + cPblr(s) + dKNO,(aq)

In an experimeflt,25.O g of lead (II) nitrate and 20.0 g of potassium iodide are dissolved separately to

form 250 cm3 of lead (II) nitrate solution and250 cm3 of potassium iodide solution. The two solutions are

then mixed together with the aim of precipitating lead (II) iodide.

(a) Determine the values of a, b, c and d.

(b) Using suitable calculations, identify the limiting reactant.

(c) What is the maximum mass of lead (II) iodide that can be obtained from the experiment?

(d) What is the concentration of potassium nitrate in the reaction mixture when the reaction is complete?

Give your answer in mol/dm3.

(e) Write an ionic equation for the above reaction and identify the spectator ion(s).

15. 3.00 g of impure sodium metal is slowly added to a beaker containing 150 cm3 of water. The resulting

sodium hydroxide solution is added to 50.0 cm3 of 1.50 mol/dm3 dilute sulfuric acid. The mixture is then

made up to250 cm3 in a volumetric flask by adding distilled water. 25.0 cm3 of this solution requires

40.0 cm3 of 0.100 mol/dm3 potassium hydroxide solution for complete neutralisation.

(a) Calculate the number of moles of potassium hydroxide required to react with the excess acid.

(b) Based on your answers in (a), calculate the number of moles of sulfuric acid present in 25.0 cm3 ofthe solution.

(c) Hence, calculate the number of moles of sulfuric acid present in 250 cm3 of the solution.

(d) Based on your answer in (c), calculate the number of moles of sulfuric acid used to react with

sodium hydroxide produced from the reaction of sodium metal with water.

(e) Hence, calculate the number of moles of sodium hydroxide produced from the reaction of sodium

metal with water.

(f) Hence or otherwise, determine the percentage purity of the sodium metal.

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