Moles Revised Edition

Subject: Chemistry (0620)

Chapter #: 6: Quantitative Chemistry How Much? (Moles)

Answer the following Questions:

Q1) May / June 2001 Question 2 part (c)

The following is a part of the description of the preparation of the soluble salt lithium chloride.

25.0 cm3 of a solution of lithium hydroxide, concentration 1.00 mol/dm3 was placed in a

beaker. A few drops of the indicator, methyl orange, were added and the mixture turned

yellow. Hydrochloric acid was added form a burette until the mixture just turned red. 20.0 cm3

of the acid was needed to neutralise the alkali.

Calculate the concentration of the hydrochloric acid.

LiOH + HCl LiCl + H2O

Number of moles of LiOH is 25 cm3 of a 1.00 mol/dm3 solution

= __________________

Therefore number of moles of HCl in 20 cm3 = __________________

Concentration of HCl = __________________

= _________________ mol/dm3

[4]

Q2) October / November 2001 Question 2 part (c)

Potassium chlorate, which has a formula of the type, KClOn, decomposes to form oxygen. 2.45 g of the chlorate produced 1.49 g of potassium chloride and 0.72dm3 of oxygen at r.t.p. Find the value of n.

KClOn KCl + n

2 O2

Mass of one mole of KCl = 74.5 g

Number of moles of KCl formed = ________________

Number of moles of oxygen molecules formed = ________________

Number of moles of oxygen atoms = ________________

Mole ratio KCl : O is ________________

n =________________ [4]

Q3) May / June 2002 Question 5 part (c) and (d)

a) A 20 cm3 sample of butyne, C4H6, is burnt in 150 cm3 of oxygen. This is an excess of oxygen.

2C4H6 (g) + 11O2 (g) 8CO2 (g) + 6H2O (l) i) What volume of oxygen reacts? _______________________________________________________________________ [1]

ii) What volume of carbon dioxide is produced? _______________________________________________________________________ [1]

iii) What is the total volume of gases left at the end of the reaction? _______________________________________________________________________ [1]

b) Calculate the mass of water formed when 9.0 g of butyne is burnt. The mass of one mole of butyne is 54 g. from the above equation, 1 mole of butyne forms 3 moles of water number of moles of butyne reacted ___________ number of moles of water formed ___________ mass of water formed ___________ g [3]

Q4) October / November 2002 Question 3 part (f)

Sodium reacts with sulphur to form sodium sulphide.

2Na + S Na2S An 11.5 g sample of sodium is reacted with 10 g of sulphur. All of the sodium reacted but there was an excess of sulphur. Calculate the mass of sulphur left unreacted. a) Number of moles of sodium atoms reacted = ___________ [2 moles of Na react with 1 mole of S] b) Number of moles of sulphur atoms that reacted = ___________ c) Mass of sulphur reacted = ___________ g d) Mass of sulphur left unreacted = ___________ g [4]

Q5) May / June 2003 Question 2 part (c)

Each tablet contains the same number of moles of CaCO3 and MgCO3. One tablet reacted with excess hydrochloric acid to produce 0.24 dm3 of carbon dioxide at r.t.p.

CaCO3 + 2HCl CaCl2 + CO2 + H2O MgCO3 + 2HCl MgCl2 + CO2 + H2O

(a) Calculate how many moles of CaCO3 there are in one tablet.

b) Calculate the volume of hydrochloric acid, 1.0 mol /dm3, needed to react with one tablet.

number of moles of CaCO3 and Mg CO3 in one tablet = ____________

Use your answer to (a).

number of moles of HCl needed to react with one tablet = ____________

volume of hydrochloric acid, 1.0 mol /dm3, needed to react with one tablet =

____________

[2]

Q6) October / November 2003 Question 5 part (d)

Sulphur dioxide reacts with chlorine in an addition reaction to form sulphuryl chloride.

SO2 + Cl2 SO2Cl2 8.0 g of sulphur dioxide was mixed with 14.2 g of chlorine. The mass of one mole of SO2Cl2 is 135 g. Calculate the mass of sulphuryl chloride formed by this mixture.

Calculate the number of moles of SO2 in the mixture = ______________

Calculate the number of moles of Cl2 in the mixture = ______________ Which reagent was not in excess? ______________

How many moles of SO2Cl2 were formed = ______________ Calculate the mass of sulphuryl chloride formed = ______________ g [5]

number of moles CO2 = ____________

number of moles of CaCO3 and MgCO3 = ____________

number of moles of CaCO3 = ____________

[3]

Q7) May / June 2004 Question 7

Chemists use the concept of the mole to calculate the amounts of chemicals involved in a reaction. a) Define mole. ________________________________________________________________________[1]

b) 3.0 g of magnesium was added to 12.0 g of ethanoic acid.

Mg + 2CH3COOH (CH3COO)2Mg + H2 The mass of one mole of Mg is 24 g.

The mass of one mole of CH3COOH is 60 g. i) Which one, magnesium or ethanoic acid, is in excess? You must show your reasoning. ________________________________________________________________________[3]

ii) How many moles of hydrogen were formed? ________________________________________________________________________[1]

iii) Calculate the volume of hydrogen formed, measured at r.t.p. ________________________________________________________________________[2]

c) In an experiment, 25.0cm3 of aqueous sodium hydroxide, 0.4mol /dm3, was neutralised by

20.0cm3 of aqueous oxalic acid, H2C2O4.

2NaOH + H2C2O4 Na2C2O4 +2H2O Calculate the concentration of the oxalic acid in mol /dm3.

i) Calculate the number of moles of NaOH in 25.0 cm3 of 0.4 mol /dm3 solution. ________________________________________________________________________[1]

ii) Use your answer to i) and the mole ratio in the equation to find out the number of moles of

H2C2O4 in 20 cm3 of solution.

________________________________________________________________________[1]

iii) Calculate the concentration, mol /dm3, of the aqueous oxalic acid. ________________________________________________________________________[2]

Q8) October / November 2004 Question 7 part (c)

Iron(III) sulphate decomposes when heated. Calculate the mass of iron(III) oxide formed and the volume of sulphur trioxide produced when 10.0 g of iron(III) sulphate was heated.

Mass of one mole of Fe2(SO4)3 is 400 g.

Fe2(SO4)3 (s) Fe2O3 (s) + 3SO3 (g) Number of moles of Fe2(SO4)3 = _________________

Number of moles of Fe2O3 formed = _________________

Mass of iron(III) oxide formed = _________________ g

Number of moles of SO3 produced = _________________

Volume of sulphur trioxide at r.t.p. = _________________ dm3

[5]

Q9) May / June 2005 Question 5 part (d)

Gypsum is hydrated calcium sulphate, CaSO4.xH2O. It contains 20.9% water by mass. Calculate x.

Mr: CaSO4, 136; H2O, 18.

79.1 g of CaSO4 = ________________________________________________ moles

20.9 g of H2O = __________________________________________________ moles x = _____________________________ [3]

Q10) October / November 2005 Question 6 part (a)

a) The following method is used to make crystals of hydrated nickel sulphate. An excess of nickel carbonate, 12.0 g, was added to 40 cm3 of sulphuric acid, 2.0 mol/dm3. The unreacted nickel carbonate was filtered off and the filtrate evaporated to obtain the crystals.

NiCO3 + H2SO4 NiSO4 + CO2 + H2O

NiSO4 + 7H2O NiSO4.7H2O Mass of one mole of NiSO4.7H2O = 281 g Mass of one mole of NiCO3 = 119 g i) Calculate the mass of unreacted nickel carbonate. Number of moles of H2SO4 in 40 cm3 of 2.0 mol/dm3 acid = 0.08 Number of moles of NiCO3 reacted = _________________

Mass of nickel carbonate reacted = _________________ g

Mass of unreacted nickel carbonate = _________________ g

[3] (ii) The experiment produced 10.4 g of hydrated nickel sulphate. Calculate the percentage yield. The maximum number of moles of NiSO4 .7H2O that could be formed = ____________________________________________________________________ The maximum mass of NiSO4 .7H2O that could be formed = __________________ g The percentage yield = ___________________________________________ % [3]


Propene reacts with hydrogen iodide to form 2 iodoprpane.

CH3CH=CH2 + HI CH3CHICH3 1.4 g of propene produced 4.0 g of 2 - iodopropane. Calculate the percentage yield.

moles of CH3CH=CH2 reacted = __________________________

maximum moles of CH3CHICH3 that could be formed = ___________________

mass of one mole of CH3CHICH3 = 170 g

maximum mass of 2 - iodopropane that could be formed = ___________________

percentage yield _________________________ %

[4]

Q12) October / November 2006 Question 6 part (a)

An ore of copper is the mineral, chalcopyrite. This is a mixed sulphide of iron and copper. Analysis of a sample of this ore shows that 13.80 g of the ore contained 4.80 g of copper, 4.20 g of iron and the rest sulphur. Complete the table and calculate the empirical formula of chalcopyrite.

copper iron sulphur

composition by mass / g

4.80

4.20

number of moles of atoms

simplest mole ratio of atoms

[3] The empirical formula is ________________________________________________________________________[1]


A better way of measuring the degree of unsaturation is to find the iodine number of the unsaturated compound. This is the mass of iodine that reacts with all the double bonds in 100 g of the fat. Use the following information to calculate the number of double bonds in one molecule of the fat.

Mass of one mole of the fat is 884 g.

One mole of I2 reacts with one mole C = C . The iodine number of the fat is 86.2 g. Complete the following calculation. 100 g of fat reacts with 86.2 g of iodine. 884 g of fat reacts with ________________________ g of iodine. One mole of fat reacts with ________________________ moles of iodine molecules. Number of double bonds in one molecule of fat is ________________________ [3]

Q14) October / November 2007 Question 7 part (b) (ii)

A small piece of marble, calcium carbonate, was added to 5 cm3 of hydrochloric acid at 25C. The time taken for the reaction to stop was measured.

CaCO3 (s) + 2HCl (aq) CaCl2 (aq) + CO2 (g) + H2O (l)

One piece of marble, 0.3 g, was added to 5 cm3 of hydrochloric acid, concentration 1.00 mol /

dm3. Which reagent is in excess? Give a reason for your choice.

mass of one mole of CaCO3 = 100 g

number of moles of CaCO3 = __________________________________________________ number of moles of HCl = _____________________________________________________ reagent in excess is _________________________________________________________ reason _________________________________________________________________ [4]

Q15) May / June 2008 Variant 31 Question 7 part (b)

Using 25.0 cm3 of aqueous sodium hydroxide, 2.24 mol / dm3, 3.86 g of crystals were obtained. Calculate the percentage yield.

2NaOH + H2SO4 Na2SO4 + 2H2O

Na2SO4 + 10H2O Na2SO4.10H2O Number of moles of NaOH used =

Maximum number of moles of Na2SO4.10H2O that could be formed =

Mass of one mole of Na2SO4.10H2O = 322 g Maximum yield of sodium sulphate-10-water = _____________________________ g Percentage yield = __________________________% [4]


Using 25.0 cm3 of aqueous sodium hydroxide, 2.64 mol / dm3, 3.95 g of crystals were obtained. Calculate the percentage yield.


Na2SO4 + 10H2O Na2SO4.10H2O Number of moles of NaOH used =

Maximum number of moles of Na2SO4.10H2O that could be formed =

Mass of one mole of Na2SO4.10H2O = 322 g Maximum yield of sodium sulphate-10-water = _____________________________ g Percentage yield = __________________________% [4]

Q17) October / November 2008 Variant 31 Question 4 part (b)

Across the world, food safety agencies are investigating the presence of minute traces of the toxic hydrocarbon, benzene, in soft drinks. It is formed by the reduction of sodium benzoate by vitamin C.

Sodium benzoate is a salt, it has the formula C6H5COONa. It can be made by the neutralisation of benzoic acid by sodium hydroxide. Benzene contains 92.3% of carbon and its relative molecular mass is 78. a) What is the percentage of hydrogen in benzene? ________________________________________________________________________[1]

b) Calculate the ratio of moles of C atoms: moles of H atoms in benzene. __________________________________________________________________________

_______________________________________________________________________ [1]

c) Calculate its empirical formula and then its molecular formula. The empirical formula of benzene is __________________________________

The molecular formula of benzene is __________________________________

[2]

Q18) October / November 2008 Variant 31 Question 7 part (a) (i)

The alkanes are generally unreactive. Their reactions include combustion, substitution and

cracking .The complete combustion of an alkane gives carbon dioxide and water.

10 cm3 of butane is mixed with 100 cm3 of oxygen, which is an excess. The mixture is

ignited. What is the volume of unreacted oxygen left and what is the volume of carbon

dioxide formed ?

C4H10 (g) + 61

2 O2 (g) 4CO2 (g) + 5H2O (l)

Volume of oxygen left = ___________________________ cm3

Volume of carbon dioxide formed = ___________________________ cm3

[2]

Q19) May / June 2009 Variant 31 Question 9

Quantities of chemicals, expressed in moles, can be used to find the formula of a compound, to establish an equation and to determine reacting masses. a) A compound contains 72% magnesium and 28% nitrogen. What is its empirical formula? __________________________________________________________________________

__________________________________________________________________________

__________________________________________________________________________

_______________________________________________________________________ [2]

b) A compound contains only aluminium and carbon. 0.03 moles of this compound reacted

with excess water to form 0.12 moles of Al(OH)3 and 0.09 moles of CH4. Write a balanced equation for this reaction. __________________________________________________________________________

__________________________________________________________________________

__________________________________________________________________________

_______________________________________________________________________ [2]

c) 0.07 moles of silicon reacts with 25 g of bromine.

Si + 2Br2 SiBr4

i) Which one is the limiting reagent? Explain your choice. __________________________________________________________________________

__________________________________________________________________________

__________________________________________________________________________

_______________________________________________________________________ [3]

ii) How many moles of SiBr4 are formed? _______________________________________________________________________ [1]

Q20) May / June 2009 Variant 32 Question 9

Part (a) and (b) are same as it is in Q19) part (a) and (b) only part (c) form this variant is different, so for part (a) and (b) of this question refer Q19) part (a) and (b). c) 0.08 moles of silicon reacts with 7.2g of fluorine.

Si + 2F2 SiF4

i) Which one is the limiting reagent? Explain your choice. __________________________________________________________________________

__________________________________________________________________________

__________________________________________________________________________

_______________________________________________________________________ [3]

ii) How many moles of SiF4 are formed? _______________________________________________________________________ [1]


9.12 g of anhydrous iron(II) sulfate was heated. Calculate the mass of iron(III) oxide formed and the volume of sulfur trioxide, at r.t.p., formed.

2FeSO4 (s) Fe2O3 (s) + SO2 (g) + SO3 (g)

mass of one mole of FeSO4 = 152 g

number of moles of FeSO4 used = _______________

number of moles of Fe2O3 formed

= _______________

mass of one mole of Fe2O3

= _______________ g

mass of iron (III) oxide formed

= _______________ g

number of moles of SO3 formed

= _______________

volume of sulfur trioxide formed

= _______________ dm3 [6]

Q22) May / June 2010 Variant 31 Question 7 part (e)

Titanium is a transition element. It is isolated by the following reactions. titanium ore titanium(IV) oxide titanium(IV) chloride titanium

TiO2 TiCl 4 Ti The titanium ore contains 36.8% iron, 31.6% titanium and the remainder is oxygen. i) Determine the percentage of oxygen in this titanium compound. percentage of oxygen = __________________________________ % [1] ii) Calculate the number of moles of atoms for each element. The number of moles of Fe is shown as an example. number of moles of Fe = 36.8 / 56 = 0.66 number of moles of Ti = ______________________________________________________ number of moles of O = ____________________________________________________ [1] iii) What is the simplest ratio for the moles of atoms?

Fe : Ti : O

_______ _______ _______

[1] iv) What is the formula of this titanium compound? _______________________________________________________________________ [1]

Q23) May / June 2010 Variant 32 Question 8 part (c)

A 5.00 g sample of impure lead(II) nitrate was heated. The volume of oxygen formed was

0.16dm3 measured at r.t.p. The impurities did not decompose. Calculate the percentage of lead(II) nitrate in the sample.

2Pb(NO3)2 2PbO + 4NO2 + O2 Number of moles of O2 formed = ________________________

Number of moles of Pb(NO3)2 in the sample = ________________________

Mass of one mole of Pb(NO3)2 = 331 g Mass of lead(II) nitrate in the sample = ________________________ g Percentage of lead(II) nitrate in sample =________________________

[4]


6.0 g of cobalt(II) carbonate was added to 40 cm3 of hydrochloric acid, concentration 2.0 mol

/dm3. Calculate the maximum yield of cobalt(II) chloride 6 water and show that the cobalt(II) carbonate was in excess.

CoCO3 + 2HCl CoCl2 + CO2 + H2O CoCl2 + 6H2O CoCl 2.6H2O

Maximum yield Number of moles of HCl used = _________________

Number of moles of CoCl2 formed = _________________

Number of moles of CoCl2.6H2O formed = _________________ Mass of one mole of CoCl2.6H2O = 238 g

Maximum yield of CoCl2.6H2O = _________________ g [4]

To show that cobalt(II) carbonate is in excess Number of moles of HCl used = _________________ (use value from above)

Mass of one mole of CoCO3 = 119 g

Number of moles of CoCO3 in 6.0 g of cobalt(II) carbonate = _________________ [1] Explain why cobalt(II) carbonate is in excess ________________________________ _______________________________________________________________________ [1]

Q25) October / November 2010 Variant 32 Question 7 part (d)

20.0 cm3 of sulfuric acid, concentration 0.30 mol / dm3, was added to 40 cm3 of sodium

hydroxide, concentration 0.20 mol / dm3.


a) How many moles of H2SO4 were added? _________________ [1] b) How many moles of NaOH were used? _________________ [1] c) Which reagent is in excess? Give a reason for your choice. reagent in excess _________________________________________________________ [1] reason ____________________________________________________________________ _______________________________________________________________________ [1]


Maleic acid is an unsaturated acid. 5.8 g of this acid contained 2.4 g of carbon, 0.2 g of hydrogen and 3.2 g of oxygen. a) How do you know that the acid contained only carbon, hydrogen and oxygen? __________________________________________________________________________ _______________________________________________________________________ [1] b) Calculate the empirical formula of maleic acid. Number of moles of carbon atoms = _________________ Number of moles of hydrogen atoms = _________________ Number of moles of oxygen atoms = _________________ The empirical formula is ____________________________________________________ [3]

Q27) May / June 2011 Variant 31 Question 7 Excess hydrochloric acid was added to powdered zinc. The hydrogen evolved was collected and its volume measured every 20 seconds. The experiments were repeated at the same temperature using the same number of moles of powdered magnesium and aluminium.

a) Identify metals A, B and C by choosing from zinc, magnesium and aluminium. Give a reason for each choice. metal A ___________________________________________________________________ __________________________________________________________________________ metal B ___________________________________________________________________ __________________________________________________________________________ metal C ___________________________________________________________________ _______________________________________________________________________ [5]

b) Using moles, explain why two of the metals form the same volume of hydrogen but the third metal forms a larger volume. __________________________________________________________________________ __________________________________________________________________________ _______________________________________________________________________ [3]

Q28) May / June 2011 Variant 32 Question 7 part (a) (iii) Hydrocarbons are compounds which contain only carbon and hydrogen.

20cm3 of a gaseous hydrocarbon was burned in 120cm3 of oxygen, which is in excess. After

cooling, the volume of the gases remaining was 90cm3. Aqueous sodium hydroxide was

added to remove carbon dioxide, 30 cm3 of oxygen remained. All volumes were measured at r.t.p..

a) Complete the following.

volume of gaseous hydrocarbon = _____________ cm3

volume of oxygen used = _____________ cm3

volume of carbon dioxide formed = _____________ cm3 [2] b) Use the above volume ratio to find the mole ratio in the equation below and hence find the formula of the hydrocarbon.

______ CxHy (g) + ______ O2 (g) ______ CO2 (g) + ______ H2O (l)

hydrocarbon formula = __________________________ [2]

Q29) October / November 2011 Variant 31 Question 7 part (c) There are three possible equations for the thermal decomposition of sodium hydrogencarbonate.

2NaHCO3 (s) Na2O (s) + 2CO2 (g) + H2O (g) equation 1

NaHCO3 (s) NaOH (s) + CO2 (g) equation 2

2NaHCO3 (s) Na2CO3 (s) + CO2 (g) + H2O (g) equation 3 The following experiment was carried out to determine which one of the above is the correct equation. A known mass of sodium hydrogencarbonate was heated for ten minutes. It was then allowed to cool and weighed. Results Mass of sodium hydrogencarbonate = 3.36 g Mass of the residue = 2.12 g Calculation

Mr for NaHCO3 = 84g; Mr for Na2O = 62g; Mr for NaOH = 40g

Mr for Na2CO3 = 106 g

a) Number of moles of Na2CO3 used = __________ [1]

b) if residue is Na2O, number of moles of Na2O = __________ If residue is NaOH, number of moles of NaOH = __________

If residue is Na2CO3, number of moles of Na2CO3 = __________ [2]

c) Use the number of moles calculated in (a) and (b) to decide which one of the three equations is correct. Explain your choice. __________________________________________________________________________ __________________________________________________________________________ _______________________________________________________________________ [2]

Q30) October / November 2011 Variant 32 Question 6 part (c) Insoluble salts are made by precipitation. An equation for the preparation of barium sulfate is given below.

BaCl2 (aq) + MgSO4 (aq) BaSO4 (s) + MgCl2 (aq) This reaction can be used to find x in the formula for hydrated magnesium sulfate

MgSO4.xH2O.

A known mass of hydrated magnesium sulfate, MgSO4.xH2O, was dissolved in water. Excess aqueous barium chloride was added. The precipitate of barium sulfate was filtered, washed and dried. Finally it was weighed. Mass of hydrated magnesium sulfate = 1.476 g Mass of barium sulfate formed = 1.398 g

The mass of one mole of BaSO4 = 233 g

The number of moles of BaSO4 formed = __________ [1]

The number of moles of MgSO4.xH2O = __________ [1]

The mass of one mole of MgSO4.xH2O = __________ g [1]

The mass of one mole of MgSO4 = 120 g The mass of xH2O in one mole of MgSO4.xH2O = __________ [1] x = __________

[1]

Q31) October / November 2011 Variant 33 Question 7 part (a) and (b)(iii) The alkenes are a series of unsaturated hydrocarbons. They have the general molecular formula CnH2n. a) Deduce the molecular formula of an alkene which has a relative molecular mass of 126. Show your working. __________________________________________________________________________ _______________________________________________________________________ [2] b) Bond energy is the amount of energy, in kJ, which must be supplied to break one mole of the bond.

Use the data in the table to show that the following reaction is exothermic.

__________________________________________________________________________ __________________________________________________________________________ _______________________________________________________________________ [3]

Q32) May / June 2012 Variant 31 Question 8 part (b) A sample of rust had the following composition: 51.85 g of iron 22.22 g of oxygen 16.67 g of water. Calculate the following and then write the formula for this sample of rust. number of moles of iron atoms, Fe = ____________

[1] number of moles of oxygen atoms, O = ____________

[1]

number of moles of water molecules, H2O =____________ [1]

simplest mole ratio Fe : O : H2O is ______ : ______ : ______ formula for this sample of rust is ____________ [1]

bond bond energy in kJ / mol

H H +436

C == C +610

C C +346

C H +415

Q33) May / June 2012 Variant 32 Question 7 part (e) 0.01 moles of an alkene needed 2.4 g of oxygen for complete combustion. 2.2 g of carbon dioxide were formed. Determine the following mole ratio.

moles of alkene : moles of O2 : moles of CO2 From this ratio determine the formula of the alkene. _______________________________________________________________________ [3] Write an equation for the complete combustion of this alkene. _______________________________________________________________________ [1]

Q34) October / November 2012 Variant 31 Question 7 part (c)

Strontium chloride-6-water can be made from the insoluble compound, strontium carbonate, by the following reactions.

SrCO3 (s) + 2 HCl (aq) Sr Cl2 (aq) + CO2 (g) + H2O (l)

SrCl 2 (aq) + 6H2 O (l) SrCl2.6H2O(s) The following method was used to prepare the crystals. 1 Add excess strontium carbonate to hot hydrochloric acid. 2 Filter the resulting mixture. 3 Partially evaporate the filtrate and allow to cool.

4 Filter off the crystals of SrCl2.6H2O. 5 Dry the crystals between filter papers.

In the above experiment, 50.0 cm3 of hydrochloric acid of concentration 2.0 mol / dm3 was

used. 6.4 g of SrCl2.6H2O was made. Calculate the percentage yield. number of moles of HCl used = ________________

number of moles of SrCl2.6H2O which could be formed = ________________

mass of one mole of SrCl2.6H2O is 267 g

theoretical yield of SrCl2.6H2O = ________________ g percentage yield = ________________ % [4]

Q35) October / November 2012 Variant 32 Question 5 part (d) Sulfur dioxide can also be made by the reaction between a sulfite and an acid.

Na2SO3 + 2HCl 2NaCl + SO2 + H2O Excess hydrochloric acid was added to 3.15 g of sodium sulfite. Calculate the maximum volume, measured at r.t.p., of sulfur dioxide which could be formed.

The mass of one mole of Na2SO3 is 126 g.

__________________________________________________________________________ __________________________________________________________________________ _______________________________________________________________________ [3]

Q36) October / November 2012 Variant 33 Question 5 part (c) (ii) An organic compound has a molecular formula C6H8O4. It is an unsaturated carboxylic acid. One mole of the compound reacts with two moles of sodium hydroxide. How many moles of COOH groups are there in one mole of this compound? _______________________________________________________________________ [1]

Q37) October / November 2012 Variant 33 Question 7 part (d) (ii) Bond breaking is an endothermic process. Bond energy is the amount of energy needed to break or form one mole of the bond. Complete the table and explain why the forward reaction is exothermic.

bond bond energy

kJ / mol energy change

kJ exothermic

or endothermic

N N 944 +944 Endothermic

H H 436 3 436 = +1308

N H 388

__________________________________________________________________________ __________________________________________________________________________ _______________________________________________________________________ [3]

Q38) May / June 2013 Variant 31 Question 4 part (b) The structural formula of cyclohexane is drawn below.

What are the molecular and empirical formulae of cyclohexane? molecular formula ________________ empirical formula ________________

[2]


The concentration of the hydrochloric acid was 2.20 mol / dm3. The volume of acid needed to neutralise the 25.0 cm3 of lithium hydroxide was 20.0 cm3. Calculate the concentration of the aqueous lithium hydroxide.

LiOH + HCl LiCl + H2O

__________________________________________________________________________ __________________________________________________________________________ _______________________________________________________________________ [2]


a) Define the following i) the mole __________________________________________________________________________ _______________________________________________________________________ [2] ii) the Avogadro constant __________________________________________________________________________ _______________________________________________________________________ [1]

b) Which two of the following contain the same number of molecules? Show how you arrived at your answer. 2.0 g of methane, CH4 8.0 g of oxygen, O2 2.0 g of ozone, O3 8.0 g of sulfur dioxide, SO2 __________________________________________________________________________ __________________________________________________________________________ _______________________________________________________________________ [2]

c) 4.8 g of calcium is added to 3.6 g of water. The following reaction occurs.

Ca + 2H2O Ca(OH)2 + H2 i) the number of moles of Ca = _______________ the number of moles of H2O = ________________ [1] ii) Which reagent is in excess? Explain your choice. __________________________________________________________________________ _______________________________________________________________________ [2] iii) Calculate the mass of the reagent named in (ii) which remained at the end of the experiment. __________________________________________________________________________ _______________________________________________________________________ [1]

Q41) May / June 2013 Variant 33 Question 7 part (d)

20cm3 of a hydrocarbon was burnt in 175cm3 of oxygen. After cooling, the volume of the remaining gases was 125cm3. The addition of aqueous sodium hydroxide removed carbon dioxide leaving 25cm3 of unreacted oxygen. i) volume of oxygen used = _____________ cm3

[1] ii) volume of carbon dioxide formed = ___________ cm3

[1] iii) Deduce the formula of the hydrocarbon and the balanced equation for the reaction. __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________ _______________________________________________________________________ [2]

Q42) October / November 2013 Variant 31 Question 4 part (d) Calculate the maximum mass of carbon dioxide given off when 20.0 g of small lumps of calcium carbonate react with 40 cm3 of hydrochloric acid, concentration 2.0 mol / dm3.

CaCO3(s) + 2HCl (aq) CaCl 2(aq) + H2O(l) + CO2(g) number of moles of HCl used =

mass of carbon dioxide = _______________ g [4]

Q43) October / November 2013 Variant 31 Question 6 part (c) Basic lead(II) carbonate has a formula of the type xPbCO3.yPb(OH)2 where x and y are whole numbers. Determine x and y from the following information.

PbCO3 PbO + CO2

Pb(OH)2 PbO + H2O When heated, the basic lead(II) carbonate gave 2.112 g of carbon dioxide and 0.432 g of water. Mass of one mole of CO2 = 44 g Mass of one mole of H2O = 18 g Number of moles of CO2 formed = ________________

[1] Number of moles of H2O formed = ________________

[1] x = _____________ and y = _____________ Formula of basic lead(II) carbonate is ______________________________________

[1]

Q44) October / November 2013 Variant 32 Question 5 part (c) (iii) Silver(I) chromate(VI) is an insoluble salt. It is prepared by precipitation. 20 cm3 of aqueous silver(I) nitrate, concentration 0.2 mol / dm3, was mixed with 20 cm3 of aqueous potassium chromate(VI), concentration 0.1 mol / dm3. After stirring, the mixture was filtered. The precipitate was washed several times with distilled water. The precipitate was then left in a warm oven for several hours.

2AgNO3 (aq) + K2CrO4 (aq) Ag2CrO4 (s) + 2KNO3 (aq)

What is the maximum mass of silver(I) chromate(VI) which could be obtained from 20 cm3 of aqueous silver(I) nitrate, concentration 0.2 mol / dm3?

number of moles of AgNO3 used = __________________

[1]

number of moles of Ag2CrO4 formed = __________________ [1]

mass of one mole of Ag2CrO4 = 332 g mass of Ag2CrO4 formed = __________________ g

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Q45) October / November 2013 Variant 33 Question 6 part (d) (i) Ethanol is made from sugars by fermentation.

C6H12O6 2C2H5OH + 2CO2 The mass of one mole of glucose, C6H12O6, is 180 g. Calculate the maximum mass of ethanol which could be obtained from 72 g of glucose. __________________________________________________________________________ __________________________________________________________________________ _______________________________________________________________________ [3]

Q46) May / June 2014 Variant 31 Question 6 part (d) Hydrogen peroxide decomposes to form water and oxygen. This reaction is catalysed by manganese(IV) oxide. In the first experiment, the maximum volume of oxygen produced was 96 cm3 measured at r.t.p. Calculate the concentration of the aqueous hydrogen peroxide in mol / dm3.

2H2O2 (aq) 2H2O (l) + O2 (g)

number of moles of O2 formed = ________________________________________________ [1]

number of moles of H2O2 in 40 cm3 of solution = ___________________________________ [1]

concentration of the aqueous hydrogen peroxide in mol / dm3=________________________

_____________________ [1]

Q47) May / June 2014 Variant 32 Question 7 part (b) The soluble salt hydrated lithium sulfate is made by titration from the soluble base lithium hydroxide. Using 25.0 cm3 of aqueous lithium hydroxide, concentration 2.48 mol / dm3, 2.20 g of hydrated lithium sulfate was obtained. Calculate the percentage yield, giving your answer to one decimal place.

2LiOH + H2SO4 Li2SO4 + 2H2O

Li2SO4 + H2O Li2SO4.H2O Number of moles of LiOH used = __________________

Number of moles of Li2SO4.H2O which could be formed = __________________ Mass of one mole of Li2SO4.H2O = 128 g Maximum yield of Li2SO4.H2O = __________________ Percentage yield = __________________%

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Q48) May / June 2014 Variant 33 Question 5 part (d) and (e) Ammonia is made by the Haber process. a) The equilibrium mixture leaving the reaction chamber contains 15% ammonia. Suggest how the ammonia could be separated from the mixture.

boiling point / C

hydrogen 253

nitrogen 196

ammonia 33

__________________________________________________________________________ _______________________________________________________________________ [2] b) Ammonia is used to make nitrogen trifluoride, NF3. Nitrogen trifluoride is essential to the electronics industry. It is made by the following reaction.

Determine if the above reaction is exothermic or endothermic using the following bond energies and by completing the following table. The first line has been done as an example. Bond energy is the amount of energy, in kJ / mole, needed to break or make one mole of the bond.

bond bond energy in kJ / mole

N H 390

F F 155

N F 280

H F 565

bond bond energy in kJ / mole

N H (3 390) = 1170

F F

N F

H F

__________________________________________________________________________ _______________________________________________________________________ [4]

Q49) May / June 2014 Variant 33 Question 6 part (c)

The alkanes are a family of saturated hydrocarbons. Their reactions include combustion, cracking and substitution. The complete combustion of hydrocarbons produces carbon dioxide and water only. a) Write the equation for the complete combustion of nonane, C9H20. _______________________________________________________________________ [2] b) 20 cm3 of a gaseous hydrocarbon was mixed with an excess of oxygen, 200 cm3. The mixture was ignited. After cooling, 40 cm3 of oxygen and 100 cm3 of carbon dioxide remained. Deduce the formula of the hydrocarbon and the equation for its combustion. All volumes were measured at r.t.p.. __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________ _______________________________________________________________________ [3]

Q50) May / June 2009 Variant 31 Question 7 part (c) Hydrogen reacts with the halogens to form hydrogen halides. Bond energy is the amount of energy, in kJ, that must be supplied (endothermic) to break one mole of a bond.

Bond bond energy in kJ / mol

HH +436

ClCl +242

HCl +431

Use the above data to show that the following reaction is exothermic.

H H + Cl Cl 2H Cl

__________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________

_______________________________________________________________________ [3]

Q51) October / November 2014 Variant 31 Question 6 part (a) (ii) Esters, polyesters and fats all contain the ester linkage. Esters can be made from alcohols and carboxylic acids. For example, the ester ethyl ethanoate can be made by the following reaction.

CH3COOH + CH3CH2OH CH3COOCH2CH3 + H2O

6.0 g of ethanoic acid, Mr = 60, was reacted with 5.5 g of ethanol, Mr = 46. Determine which is the limiting reagent and the maximum yield of ethyl ethanoate, Mr = 88. number of moles of ethanoic acid = ___________________________________________ [1]

number of moles of ethanol = ________________________________________________ [1]

the limiting reagent is ______________________________________________________ [1]

number of moles of ethyl ethanoate formed = ___________________________________ [1]

maximum yield of ethyl ethanoate = ___________________________________________ [1]

Q52) October / November 2014 Variant 32 Question 6 part (b) (ii) A group of naturally occurring minerals have the formula of the type FeSO4.xH2O where x is 1, 4, 5, 6 or 7. The most common of these minerals is iron(II) sulfate-7-water. When this mineral is heated gently it dehydrates.

FeSO4.7H2O FeSO4 + 7H2O green pale yellow

When the iron(II) sulfate is heated strongly, further decomposition occurs.

2FeSO4(s) Fe2O3(s) + SO2(g) + SO3(g)

The gases formed in this reaction react with water and oxygen to form sulfuric acid. Explain how the sulfuric acid is formed. __________________________________________________________________________ _______________________________________________________________________ [2] A mineral of the type FeSO4.xH2O contains 37.2% of water. Complete the calculation to determine x. mass of one mole of H2O = 18 g mass of water in 100 g of FeSO4.xH2O = 37.2 g number of moles of H2O in 100 g of FeSO4.xH2O =______________

mass of FeSO4 in 100 g of FeSO4.xH2O = . ______________g mass of one mole of FeSO4 = 152 g number of moles of FeSO4 in 100 g of FeSO4.xH2O = ______________ x = ______________

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Q53) October / November 2014 Variant 33 Question 8 part (c) The preparation of crystals of the soluble salt, cobalt(II) chloride-6-water, CoCl 2.6H2O, from the insoluble base, cobalt(II) carbonate.

CoCO3(s) + 2HCl (aq) CoCl 2(aq) + CO2(g) + H2O(l)

6.31 g of cobalt(II) chloride-6-water crystals were obtained. Calculate the percentage yield to 1 decimal place. number of moles of HCl in 50 cm3 of acid, concentration 2.2 mol / dm3 = ______________ maximum number of moles of CoCl 2.6H2O, which could be formed = ______________ mass of 1 mole of CoCl 2.6H2O, = 238 g maximum yield of CoCl 2.6H2O, = ______________ g percentage yield = ______________ %

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Moles Revised Edition