# Moles and Equations - Worksheets 2.1-2.11 1 Ans

September 29, 2017 | Author: ash256 | Category: Mole (Unit), Sodium Carbonate, Gases, Acid, Chlorine

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Revision worksheet by Philip allan, Chemistry Moles and Equations Answers...

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TOPIC

2

MOLES AND EQUATIONS

2.1

Worksheet

The mole concept (1) In this question, assume that the value of the Avogadro constant, NA, is 6 × 1023 mol–1. (a) Calculate the number of magnesium atoms, Mg, in 4 g of magnesium. [Relative atomic mass Mg = 24] (2 marks) (b) Calculate the number of carbon atoms, C, in 0.12 g of carbon. [Relative atomic mass C = 12] (2 marks) (c) Calculate the number of sulfur dioxide molecules, SO2, in 32 g of sulfur dioxide. [Relative atomic masses S = 32, O = 16] (2 marks) + (d) Calculate the number of sodium ions, Na , in 14.2 g of sodium sulfate. [Relative atomic masses Na = 23, S = 32, O = 16] (2 marks) (2) Calculate the number of moles of atoms present in each of the following. [Relative atomic masses are given in brackets] (a) 16.0 g of oxygen atoms [O = 16] (b) 0.14 g of nitrogen atoms [N = 14] (c) 5.4 g of silver atoms [Ag = 108] (d) 8.88 g of chlorine atoms [Cl = 35.5]

(2 (2 (2 (2

marks) marks) marks) marks)

(3) Calculate the mass, in grams, of each of the following amounts. [Relative atomic masses are given in brackets] (a) 0.5 mol of oxygen atoms [O = 16] (1 mark) (b) 10 mol of sodium atoms [Na = 23] (1 mark) (c) 0.01 mol of hydrogen atoms [H = 1] (1 mark) (d) 0.25 mol of zinc atoms [Zn = 65.4] (1 mark) (4) Calculate the molar masses, in g mol–1, of each of the following substances. (a) Br2 [Br = 80] (b) CO2 [C = 12, O = 16] (c) HNO3 [H = 1, N = 14, O = 16] (d) CuSO4 . 5H2O [Cu = 64, S = 32, O = 16, H = 1]

(1 (1 (1 (1

(5) Calculate the number of moles present in each of the following samples. (a) 128 g of oxygen, O2 [O = 16] (b) 25.25 g of potassium nitrate, KNO3 [K = 39, N = 14, O = 16] (c) 414 g of ethanol, C2H5OH [C = 12, H = 1, O = 16]

(1 mark) (1 mark) (1 mark)

(6) Calculate the mass, in grams, of each of the following amounts. (a) 2.0 mol of sulfur dioxide molecules, SO2 [S = 32, O = 16] (b) 20 mol of sulfuric acid, H2SO4 [H = 1, S = 32, O = 16] (c) 0.50 mol of sodium hydroxide, NaOH [Na = 23, O = 16, H = 1]

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(1 mark) (1 mark) (1 mark) Total: 30 marks

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2.2

Empirical formulae (1) Calculate the empirical formulae of the following compounds from the information given: (a) 1.12 g of iron combines with oxygen to form 1.60 g of an oxide of iron. [Fe = 56, O = 16] (b) 23.8 g of tin combines with chlorine to form 38.0 g of a chloride of tin. [Sn = 119, Cl = 35.5] (c) 5.8 g of aluminium combines with 22.9 g of chlorine. [Al = 27, Cl = 35.5] (d) A compound was found to contain 43.4% sodium, 11.3% carbon and 45.3% oxygen by mass. [Na = 23, C = 12, O = 16] (e) A compound contains 82.75% by mass of carbon and 17.25% by mass of hydrogen. [C = 12, H = 1] (2) Deduce the molecular formula of the compound determined in Question 1(e) above, given that its molar mass is 58 g mol–1. (3) Calculate the empirical formula of the following compounds from the percentages by mass given: (a) C = 66.67%, H = 11.11%, O = 22.22% [C = 12, H = 1, O = 16] (b) C = 40.4%, H = 7.9%, N = 15.7%, O = 36.0% [C = 12, H = 1, N = 14, O = 16] (c) 85.25% BaCl2, 14.75% water of crystallisation [Ba = 137, Cl = 35.5, H = 1, O = 16] (d) Be = 12.9%, C = 17.3%, O = 69.8% [Be = 9, C = 12, O = 16] (4) Deduce the molecular formula of each compound given the empirical formula and the molar mass of the compound in g mol–1: (a) C2H2O (molar mass = 42 g mol–1) (b) CH2O (molar mass = 120 g mol–1) (c) NaO (molar mass = 78 g mol–1) (d) CHO (molar mass = 174 g mol–1)

(2 marks) (2 marks) (2 marks) (2 marks) (2 marks) (2 marks)

(2 marks) (2 marks) (2 marks) (2 marks)

(1 (1 (1 (1

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(5) Calculate the percentage by mass of each of the stated elements in the following compounds: (2 marks) (a) Silicon in SiCl4 [Si = 28, Cl = 35.5] (2 marks) (b) Nitrogen in NH4NO3 [N = 14, H = 1, O = 16] (2 marks) (c) Sulfur in CuSO4.5H2O [Cu = 64, S = 32, O =16, H =1] Total: 30 marks

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2.3

Writing formulae (I) (1) Write formulae for the following ionic compounds. (a) sodium chloride (b) potassium iodide (c) sodium sulfate (d) magnesium nitrate (e) aluminium sulfate (f) copper(II) oxide (g) copper(I) oxide (h) silver nitrate (i) silver oxide (j) lead(II) nitrate (2) Write formulae for the following covalent compounds. (a) carbon tetrachloride (b) silicon dioxide (c) hydrogen sulfide (d) nitrogen monoxide (e) octane

(5 marks)

(3) Write formulae for the following acids. (a) hydrochloric acid (b) sulfuric acid (c) nitric acid (d) ethanoic acid (e) hydrobromic acid

(5 marks)

(4) Write names for the substances represented by the formula in each case. (a) NH3 (b) SO2 (c) H2 (d) CH4 (e) Na2CO3 (f) Ca(OH)2 (g) Cu(NO3)2 (h) CuCl (i) C4H10 (j) KAt

(10 marks)

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2.4

Writing formulae (II) (1) Balance the following equations: (a) Ca + H2O  Ca(OH)2 + H2 (b) H2SO4 + KOH  K2SO4 + H2O (c) NaNO3  NaNO2 + O2 (d) H3PO4 + NaOH  Na3PO4 + H2O (e) Fe2O3 + CO  Fe + CO2 (f) HBr + H2SO4  H2O + SO2 + Br2 (g) C4H10 + O2  CO2 + H2O (h) Pb(NO3)2  PbO + NO2 + O2 (i) Cu + HNO3  Cu(NO3)2 + NO + H2O (j) NaOH + Cl2  NaClO3 + NaCl + H2O

(1 (1 (1 (1 (1 (1 (1 (1 (1 (1

(2) Convert the following word equations into balanced symbol equations, including state symbols: (a) solid zinc + copper(II) sulfate solution  zinc sulfate solution + solid copper (1 (b) solid calcium hydroxide + solid ammonium chloride  solid calcium chloride + steam + ammonia gas (1 (c) silicon tetrachloride + water  solid silicon dioxide + hydrogen chloride gas (1 (d) gaseous octane + oxygen  carbon dioxide + steam (1 (e) sodium + water  sodium hydroxide solution + hydrogen gas (1 (3) 1.133 g of solid silver nitrate were heated. Solid silver metal (0.720 g) and gaseous nitrogen dioxide (0.307 g) were given off in addition to oxygen gas. From the data given, write a balanced equation for the reaction. [Ag = 108, N = 14, O = 16]

mark) mark) mark) mark) mark) mark) mark) mark) mark) mark)

mark) mark) mark) mark) mark)

(3 marks)

(4) Write ionic equations derived from each of the following full chemical equations: (2 marks) (a) AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq) (2 marks) (b) Zn(s) + H2SO4(aq)  ZnSO4(aq) + H2(g) (2 marks) (c) HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) (2 marks) (d) CuO(s) + H2SO4(aq)  CuSO4(aq) + H2O(l) (2 marks) (e) Pb(NO3)2(aq) + 2NaCl(aq)  PbCl2(s) + 2NaNO3(aq) (2 marks) (f) CaCO3(s) + 2HCl(aq)  CaCl2(aq) + H2O(l) + CO2(g) Total: 30 marks

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MOLES AND EQUATIONS

2.5

Reacting masses (1) Calculate the mass of magnesium chloride, MgCl2, that would be obtained when 48 g of magnesium metal is reacted completely with chlorine. [Mg = 24, Cl = 35.5] Mg(s) + Cl2(g)  MgCl2(s)

(2 marks)

(2) Calculate the mass of calcium carbonate, CaCO3, that must be decomposed in order to produce 14 tonnes of calcium oxide, CaO. [Ca = 14, C = 12, O =16] CaCO3(s)  CaO(s) + CO2(g)

(2 marks)

(3) Consider the reaction: 2SO2 + O2  2SO3 10 tonnes of sulfur dioxide, SO2, were reacted completely with oxygen in an industrial process. (a) Calculate the moles of sulfur dioxide reacted. [S = 32, O = 16] Note: 1 tonne = 1 × 106 g (2 marks) (b) Calculate the mass of sulfur trioxide, SO3, formed in tonnes, to three sig. figs. [S = 32, O = 16] (2 marks) (4) Consider the reaction: Cl2 + 2NaI  2NaCl + I2 Calculate the maximum mass of iodine, I2, that could be produced from 20.0 g of sodium iodide. [Na = 23, I = 127] (2 marks) (5) Potassium chlorate, KClO3, decomposes as shown in the equation below: 2KClO3(s)  2KCl(s) + 3O3(g) Calculate the mass of oxygen gas, O2(g), that can be produced by the complete decomposition of 1.47 g of potassium chlorate. [K = 39, Cl = 35.5, O = 16] (2 marks) (6) A two-stage industrial process is used to produce sodium carbonate, Na2CO3. Stage 1 Ammonia and carbon dioxide are reacted with aqueous sodium chloride solution. Sodium hydrogencarbonate and ammonium chloride are formed. NaCl + H2O + NH3 + CO2  NaHCO3 + NH4Cl Stage 2 Sodium hydrogencarbonate is thermally decomposed to form sodium carbonate 2NaHCO3  Na2CO3 + H2O + CO2 Calculate the maximum mass of sodium carbonate, Na2CO3, which could be formed from 546 kg of sodium chloride, NaCl. [Na = 23, Cl = 35.5, H = 1, C = 12, O = 16, N = 14]

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MOLES AND EQUATIONS

2.5 Continued

(7) Stibnite is an ore containing 5% by mass of the compound antimony sulfide, Sb2S3. The metal is produced by reduction of antimony sulfide by iron. Sb2S3 + 3Fe  2Sb + 3FeS (a) Calculate the number of moles of Sb2S3 in 680 kg of stibnite, assuming the (2 marks) sample contains 5% by mass of Sb2S3. [Sb = 122, S = 32] (b) Calculate the maximum mass of antimony, Sb, that could be obtained from 680 kg of stibnite. (1 mark) (8) 9.80 g of sulfuric acid, H2SO4, reacted with 8.50 g of sodium nitrate, NaNO3, to produce 6.30 g of nitric acid and only one other product, which is a sodium salt. Use this information to work out the equation for the reaction. (3 marks) [Molar masses/g mol–1: H2SO4 = 98, NaNO3 = 85 and HNO3 = 63] Total: 20 marks

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MOLES AND EQUATIONS

2.6

Gas volumes (1) The expression volume of one mole of gas =

mass of one mole of gas

density of the gas the volume occupied by 1 mol of gas molecules for any gas. The relative atomic masses for some elements are:

can be used to calculate

Ar = 40, Cl = 35.5, F = 19, He = 4, H = 1, Ne = 20, N = 14, O = 16, C = 12, S = 32

The densities of some gases, measured at room temperature and pressure, are given in the table below

Name of gas

Formula

Density at room temperature and pressure/g dm–3

Argon

Ar

1.66

Chlorine

Cl2

2.99

Fluorine

F2

1.58

Helium

He

0.17

Hydrogen

H2

0.08

Neon

Ne

0.84

Nitrogen

N2

1.17

Oxygen

O2

1.33

Carbon dioxide

CO2

1.81

Hydrogen sulfide

H 2S

1.41

Use the above information to complete the following table. [One line of the table has already been completed – that for oxygen – as follows: relative atomic mass of O is 16 mass of one mole of O2 is 32 g density of O2 at rtp is 1.33 g dm–3 volume of one mole of O2 gas at rtp =

32 1.33

= 24.1 dm3 ]

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2.6

Worksheet

MOLES AND EQUATIONS

Continued

Gas

Formula

Argon

Ar

Helium

He

Neon

Ne

Hydrogen

H2

Oxygen

O2

Nitrogen

N2

Chlorine

Cl2

Fluorine

F2

Carbon dioxide

CO2

Hydrogen sulfide

H 2S

Mass of 1 mol of gas/g

Volume of 1 mol of gas molecules at rtp/dm3

32

24.1

(9 marks) Note: To a good approximation, the above experimental data show that the volume occupied by one mole of any gas at room temperature and pressure is approximately 24 dm3. [In the following questions, assume that the molar volume of a gas at room temperature and pressure is 24 dm3 mol–1 (24 000 cm3 mol–1). ] (2) Calculate the number of moles of gas contained in the following volumes (all measurements at room temperature and pressure). (a) 48 dm3 of oxygen gas, O2 (1 mark) (1 mark) (b) 3 dm3 of ammonia gas, NH3 3 (1 mark) (c) 96 cm of neon gas, Ne (1 mark) (d) 240 000 cm3 of chlorine gas, Cl2 (3) Calculate the volume of the following amounts of gases at rtp. (a) 3.0 mol of nitrogen, N2 (b) 0.20 mol of neon, Ne (c) 0.50 mol of carbon dioxide, CO2

(1 mark) (1 mark) (1 mark)

(4) Calculate the volumes of the following gases at rtp. (a) 0.2 g of helium, He, in cm3 [He = 4] (b) 1.7 g of ammonia, NH3, in dm3 [N = 14, H = 1] (c) 0.056 g of ethene, C2H4, in cm3 [C = 12, H = 1] (d) 4.8 g of oxygen, O2, in dm3 [O = 16]

(1 (1 (1 (1

(5) Calculate the mass of the following volumes of gases (measured at rtp). (a) 48 dm3 of helium, He [He = 4] (b) 0.12 dm3 of oxygen, O2 [O = 16] (c) 0.72 dm3 of ammonia, NH3 [N = 14, H = 1]

(1 mark) (1 mark) (1 mark)

(6) Calculate the molar masses (g mol–1) of the following gases. (a) 0.32 g of gas X occupies 48 cm3 at rtp (b) 0.355 g of gas Y occupies 120 cm3 at rtp

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(1 mark) (1 mark) Total: 25 marks

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MOLES AND EQUATIONS

2.7

Calculating the volume of gaseous reactants and products [In the following questions, assume that the molar volume of a gas at room temperature and pressure is 24 dm3 mol–1 (24 000 cm3 mol–1).] (1) Calculate the volume of hydrogen gas, H2 (measured at room temperature and pressure) which would be formed when 12.0 g of magnesium react with excess dilute sulfuric acid. [Mg = 24] Mg(s) + H2SO4(aq)  MgSO4(aq) + H2(g)

(2 marks)

(2) Calculate the volume of carbon dioxide gas, CO2 (measured at room temperature and pressure) which would be formed when 90.0 g of glucose, C6H12O6, completely ferments according to the equation: C6H12O6(aq)  2C2H5OH(aq) + 2CO2(g) [C = 12, H = 1, O = 16]

(2 marks)

(3) Silane, SiH4, is a gas. (a) Calculate the number of moles in 8 g of silane. [Si = 28, H = 1] (b) The equation for the combustion of silane is shown below:

(1 mark)

SiH4(g) + 2O2(g)  SiO2(s) + 2H2O(l) (i) Calculate the number of moles of oxygen required to burn 8 g of silane. (1 mark) (ii) Calculate the volume of oxygen, at room temperature and pressure, needed to burn 8 g of silane. (1 mark) (4) Potassium chlorate, KClO3, decomposes on heating as shown below. 2KClO3(s)  2KCl(s) + 3O2(g) Calculate the mass of KClO3 required to produce 1.00 dm3 of oxygen gas, O2, at room temperature and pressure. [K = 39, Cl = 35.5, O = 16]

(2 marks)

(5) Chlorine reacts with sodium iodide as shown in the equation below: Cl2(g) + 2KI(aq)  2KCl(aq) + I2(s) Calculate the volume of chlorine gas, measured at room temperature and pressure, required to produce 25.4 g of solid iodine (I = 127). (2 marks) (6) A car engine burns the compound octane, C8H18 2C8H18(g) + 25O2(g)  16CO2(g) + 18H2O(l) Calculate: (a) the volume of oxygen required to completely burn 2 dm3 of octane vapour (1 mark) (b) the volume of carbon dioxide gas you would expect to be formed (1 mark) [Assume that all gas volumes are measured at the same temperature and pressure.]

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MOLES AND EQUATIONS

2.7 Continued

(7) Consider the following reaction: CO2(g) + C(s)  2CO(g) What volume of carbon monoxide would be made from 100 cm3 of carbon dioxide? (1 mark) [Assume that all gas volumes are measured at the same temperature and pressure.] (8) Consider the reaction: 4NH3(g) + 5O2(g)  4NO(g) + 6H2O(l) If 80 dm3 of ammonia, NH3, completely react according to the above equation calculate: (a) the volume of nitrogen monoxide, NO, that would be produced. (1 mark) 3 (b) the minimum volume of air that would be required to react with 80 dm of ammonia. [Note: assume air is 20% oxygen and that all gas volumes are measured at the same temperature and pressure.] (2 marks) (9) Sodium peroxide, Na2O2, reacts with carbon dioxide, CO2, as shown in the equation below. 2Na2O2(s) + 2CO2(g)  2Na2CO3(s) + O2(g) Calculate the volume of oxygen gas (measured at room temperature and pressure) that would be obtained when 0.39 g of sodium peroxide completely reacts with excess carbon dioxide. (1 mark) (10) When 1,2-dibromoethane, BrCH2CH2Br, is reacted with sodium iodide, NaI, the following reaction occurs. BrCH2CH2Br + 2NaI  C2H4 + I2 + 2NaBr 15.7 g of 1,2-dibromoethane was completely reacted with excess sodium iodide. Calculate the maximum volume of ethene gas, C2H4, (measured at room temperature and pressure) that would be formed in this reaction. [C = 12, H = 1, Br = 80] (2 marks) Total: 20 marks

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MOLES AND EQUATIONS

2.8

Amounts in solution (1) What is meant by the term standard solution? (2 marks) (2) 0.100 mol of sodium hydroxide was placed in each of the four volumetric flasks shown below and diluted to the volumes shown. Calculate the concentration (4 marks) of the solution formed in each case, in mol dm–3.

V = 2000 cm3

V = 500 cm3

V = 250 cm3

V = 100 cm3

(3) Calculate the concentration (in mol dm–3) of the following solutions: (a) 0.001 mol KOH in 20 cm3 of solution (b) 0.006 mol H2SO4 in 0.075 dm3 of solution (c) 0.012 mol CuSO4 in 0.20 dm3 of solution (d) 0.40 mol of AgNO3 in 1250 cm3 of solution (4) Calculate the concentration (in mol dm–3) of the following solutions: (a) 4.9 g of H2SO4 in 100 cm3 of solution [H = 1, S = 32, O =16] (b) 3.31 g of Pb(NO3)2 in 2.5 dm3 of solution [Pb = 207, N = 14, O = 16] (c) 0.106 g of Na2CO3 in 25.0 cm3 of solution [Na = 23, C = 12, O = 16] (d) 125 g of CuSO4.5H2O in 5.0 dm3 of solution [Cu = 64, S = 32, O = 16, H = 1] (5) Calculate the mass of: (a) calcium chloride, CaCl2, required to make 100 cm3 of a solution, concentration 2.0 mol dm–3. [Ca = 40, Cl = 35.5] (b) pure sulfuric acid, H2SO4, required to make 0.500 dm3 of a solution, concentration 5.0 mol dm–3. [H = 1, S = 32, O = 16] (c) sodium chloride, NaCl, required to make 200 cm3 of a solution, concentration 0.50 mol dm–3. [Na = 23, Cl = 35.5]

(1 (1 (1 (1

mark) mark) mark) mark)

(1 mark) (1 mark) (1 mark) (1 mark)

(2 marks) (2 marks) (2 marks)

(6) Calculate the number of moles of solute present in each of the following solutions: (a) 250 cm3 of 0.200 mol dm–3 KMnO4 (1 mark) 3 –3 (1 mark) (b) 200 cm of 0.117 mol dm NaOH 3 –3 (1 mark) (c) 2.00 dm of 0.100 mol dm NaCl (1 mark) (d) 0.100 dm3 of 2.00 mol dm–3 H2SO4

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2.8

Worksheet

Continued (7) Express the following molar concentrations (mol dm–3) in units of g dm–3: (a) 0.200 mol dm–3 KMnO4 [K = 39, Mn = 55, O = 16] (b) 0.117 mol dm–3 NaOH [Na = 23, O = 16, H = 1] (c) 0.100 mol dm–3 NaCl [Na = 23, Cl = 35.5] (d) 0.500 mol dm–3 Al2(SO4)3 [Al = 27, S = 32, O = 16]

(1 (1 (1 (1

(8) A sample of battery acid contains 1176 g of sulfuric acid, H2SO4, in 3.0 dm3 of liquid. Calculate the concentration of the sulfuric acid in: (a) g dm–3 (b) mol dm–3 [Assume H = 1, S = 32, O = 16]

mark) mark) mark) mark)

(1 mark) (1 mark)

Total: 30 marks

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2.9

Acids and bases (1) What do you understand by the term acid?

(2 marks)

(2) Copy and complete the table.

(3 marks)

Name of chemical

Formula

Hydrochloric acid Sulfuric acid Nitric acid

(3) What do you understand by the term alkali?

(2 marks)

(4) Copy and complete the table.

(3 marks)

Name of chemical

Formula

Sodium hydroxide Potassium hydroxide Ammonia

(5) What do you understand by the term salt? (6) Define the following terms: (a) anhydrous (b) hydrated (c) water of crystallisation

(2 marks) (1 mark) (1 mark) (1 mark)

(7) The molar mass of anhydrous sodium carbonate, Na2CO3, is 106 g mol–1 and that of water, H2O is 18 g mol–1. 0.572 g of hydrated sodium carbonate, Na2CO3.xH2O, was heated to constant mass. The residue weighed 0.212 g. (a) Calculate the number of moles of water that were driven off. (1 (b) Calculate the number of moles of anhydrous sodium carbonate in the residue. (1 (c) Deduce the formula of hydrated sodium carbonate. (1 (d) Why was the hydrated sodium carbonate heated to constant mass? (1 (8) A hydrated salt has the empirical formula FeN3H12O15. Deduce the formula of the salt, showing the moles of water of crystallisation after the dot.

mark) mark) mark) mark)

(1 mark)

(9) 5.50 g of a hydrated sample of iron(III) oxide, Fe2O3.xH2O, was heated until all the water was driven off. 4.71 g of anhydrous solid was left. Deduce the formula of the hydrated compound. [Fe = 56, O = 16, H = 1] (2 marks)

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2.9 Continued

(10) Write both (i) the full equation and then (ii) the ionic equation for each of the following reactions: (a)magnesium + hydrochloric acid  magnesium chloride + hydrogen (2 marks) [Assume the solid magnesium oxide and solid magnesium carbonate are insoluble when writing the ionic equations for parts (b) and (c).] (b) magnesium oxide + hydrochloric acid  magnesium chloride + water (2 marks) (c)magnesium carbonate + hydrochloric acid  magnesium chloride + water + carbon dioxide (2 marks) (11) Ethanoic acid, CH3COOH, is the acid present in vinegar. Write the equation for the reaction between aqueous sodium carbonate solution and dilute ethanoic acid. Include all state symbols. (1 mark) (12) Aqueous ammonia reacts with dilute ethanoic acid to form a solution of ammonium ethanoate. Write the equation for this reaction, including all state symbols. (1 mark) Total: 30 marks

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2.10

Volumetric analysis: titrations (1) In a titration it was found that 28.5 cm3 of dilute nitric acid, concentration 0.100 mol dm–3, were exactly neutralised by 25.0 cm3 of potassium hydroxide solution. KOH(aq) + HNO3(aq)  KNO3(aq) + H2O(l) Calculate the concentration of the potassium hydroxide solution, in mol dm–3.

(2 marks)

(2) In a titration, 40.0 cm3 of aqueous potassium hydroxide solution, of concentration 5.6 g dm–3 by mass, were exactly neutralised by 40.0 cm3 dilute hydrochloric acid. KOH(aq) + HCl(aq)  KCl(aq) + H2O(l) Calculate the concentration of the hydrochloric acid in mol dm–3. [K = 39, O = 16, H = 1]

(2 marks)

(3) In a titration, 12.0 cm3 of an aqueous solution of sulfuric acid exactly neutralised 20.0 cm3 of a solution of sodium hydroxide, concentration 0.150 mol dm–3. H2SO4(aq) + 2NaOH(aq)  Na2SO4(aq) + 2H2O(l) Calculate the concentration of the aqueous sulfuric acid, in mol dm–3.

(2 marks)

(4) In a titration, 25.0 cm3 of dilute nitric acid exactly neutralised 15.0 cm3 of a dilute solution of ammonia, concentration 0.0200 mol dm–3. HNO3(aq) + NH3(aq)  NH4NO3(aq) Calculate the concentration of the nitric acid, in mol dm–3.

(1 mark)

(5) In a titration, 20.0 cm3 of dilute hydrochloric acid, concentration 0.100 mol dm–3, reacted with 25.0 cm3 of sodium carbonate solution. Na2CO3(aq) + 2HCl(aq)  2NaCl(aq) + H2O(l) + CO2(g) Calculate the concentration of the sodium carbonate solution: (a) in mol dm–3 (b) in g dm–3 [Na = 23, C = 12, O = 16]

(2 marks)

3

(6) 200 cm of aqueous solution of hydrochloric acid was prepared by dissolving gaseous hydrogen chloride in water. A 25.0 cm3 sample of the hydrochloric acid solution was transferred to a conical flask. On titration, the 25.0 cm3 portion of hydrochloric acid required 27.60 cm3 of a 0.100 mol dm–3 sodium hydroxide solution for complete neutralisation. HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) (a) Calculate the number of moles of sodium hydroxide in 27.60 cm3 of 0.100 mol dm–3 aqueous sodium hydroxide solution. (b) Deduce the number of moles of hydrochloric acid neutralised in the titration. (c) Calculate the number of moles of hydrochloric acid in the original 200 cm3 solution of the acid. (d) Calculate the concentration of the acid in mol dm–3.

INORGANIC & PHYSICAL CHEMISTRY (I): CORE CONCEPTS

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MOLES AND EQUATIONS

2.10 Continued

(7) A carbonate of metal M has the formula M2CO3. The equation for the reaction of M2CO3 with dilute hydrochloric acid is: M2CO3(s) + 2HCl(aq)  2MCl(aq) + CO2(g) + H2O(l) 0.188 g of M2CO3 was found to exactly neutralise 23.6 cm3 of dilute hydrochloric acid, concentration 0.150 mol dm–3. (a) Calculate the moles of hydrochloric acid that reacted with 0.188 g of M2CO3. (b) Calculate the number of moles of M2CO3 that reacted with the hydrochloric acid. (c) Calculate the molar mass of the metal carbonate, M2CO3. (d) Calculate the molar mass of the metal, M, and hence deduce its identity.

(1 mark) (1 mark) (1 mark) (2 marks)

(8) Lead(II) nitrate, Pb(NO3)2, may be produced by the reaction shown in the equation below. PbO(s) + 2HNO3(aq)  Pb(NO3)2(aq) + H2O(l) 3

175 cm of dilute nitric acid, concentration 1.50 mol dm–3, reacted with excess lead(II) oxide, PbO. Calculate the maximum mass of lead(II) nitrate which could have been obtained in this reaction. [Pb = 207, N = 14, O = 16] (2 marks) (9) 1.575 g of hydrated ethanedioic acid, H2C2O4.xH2O, was dissolved in 250 cm3 distilled water. In a titration, 25.0 cm3 of this acid solution was neutralised by exactly 25.0 cm3 of dilute sodium hydroxide, concentration 0.100 mol dm–3. COOH

COONa + 2H2O

+ 2NaOH COOH

COONa

The equation for the reaction is shown below (a) Calculate the number of moles of NaOH in 25.0 cm3 of a 0.100 mol dm–3 solution. (1 (b) Calculate the moles of anhydrous ethanedioic acid neutralised by 25.0 cm3 of 0.100 mol dm–3 sodium hydroxide solution. (1 (c) Calculate the number of moles of anhydrous ethanedioic acid in the weighed sample of hydrated ethanedioic acid. (1 (1 (d) Calculate the molar mass of anhydrous ethanedioic acid, H2C2O4. (e) Calculate the mass of anhydrous ethanedioic acid in the weighed sample, from your answers to parts (c) and (d). (1 (f) Calculate the mass of water of crystallisation in the hydrated acid. (1 (g) Calculate the number of moles of water of crystallisation in the hydrated acid. (1 (h) Calculate the mole ratio of anhydrous H2C2O4 : water in the solid acid and hence state the formula of the hydrated acid. (1

INORGANIC & PHYSICAL CHEMISTRY (I): CORE CONCEPTS

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2.10 Continued

(10) A student carried out an experiment to find the percentage by mass of calcium carbonate, CaCO3, in a 1.00 g sample of limestone. The student found that 50.0 cm3 of dilute hydrochloric acid, concentration 0.100 mol dm–3, reacted with the calcium carbonate in the sample. CaCO3(s) + 2HCl(aq)  CaCl2(aq) + CO2(g) + H2O(l) Calculate the percentage purity of the limestone. [Ca = 40, C = 12, O = 16] (2 marks) (11) An experiment was carried out to find the percentage purity of a sample of magnesium carbonate.  An impure sample of magnesium carbonate was added to 30.0 cm3 of a 0.100 mol dm–3 solution of dilute hydrochloric acid.  The magnesium carbonate reacted with the hydrochloric acid as shown in the equation: MgCO3(s) + 2HCl(aq)  MgCl2(aq) + CO2(g) + H2O(l)  

Some of the dilute hydrochloric acid remained unreacted. This excess acid was titrated with dilute sodium hydroxide solution. 12.3 cm3 of a 0.100 mol dm–3 solution of sodium hydroxide was required to neutralise this excess acid. HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)

(a) Calculate the moles of hydrochloric acid in 30.0 cm3 of 0.100 mol dm–3 hydrochloric acid. (b) Calculate the moles of hydrochloric acid that reacted with the magnesium carbonate. (c) Calculate the moles of magnesium carbonate, MgCO3, which reacted with the dilute hydrochloric acid. (d) Calculate the mass of magnesium carbonate in the sample. [Mg = 24, C= 12, O = 16] (e) If the weighed sample of the impure magnesium carbonate had a mass of 0.124 g, calculate the percentage purity of the solid. Total:

INORGANIC & PHYSICAL CHEMISTRY (I): CORE CONCEPTS

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2.11

Yield calculations (1) 2-chloro-2-methylpropane may be prepared from 2-methylpropan-2-ol by a reaction with concentrated hydrochloric acid. (CH3)3COH + HCl  (CH3)3CCl + H2O 2-methylpropan-2ol 2-chloro-2-methylpropane In a preparation, 5.8 g of 2-chloro-2-methylpropane was obtained from 7.9 g of 2-methylpropan-2-ol. Calculate the percentage yield of 2-chloro-2-methylpropane in this reaction. [Molar masses/g mol–1: (CH3)3COH = 74, (CH3)3CCl = 92.5] (2 marks) (2) In an organic chemistry experiment, 49.2 g of nitrobenzene (C6H5NO2) were obtained from 39.0 g of benzene (C6H6). The equation for the reaction is: C6H6(l) + HNO3(l)  C6H5NO2(l) + H2O(l) Calculate the percentage yield of the reaction. [Relative atomic masses: C = 12, H = 1, N = 14, O = 16]

(2 marks)

(3) A student carried out an experiment to prepare hydrated manganese(II) sulfate crystals, MnSO4.4H2O. An excess of powdered manganese was added to 50 cm3 of 2.00 mol dm–3 dilute sulfuric acid in a beaker. When the reaction had finished, the solution was filtered, concentrated by evaporation and set aside to crystallise. The crystals were removed, dried and weighed. The equation for the reaction is: Mn(s) + H2SO4(aq)  MnSO4(aq) + H2(g) The final mass of hydrated crystals collected, MnSO4.4H2O, was 11.15 g. Calculate the percentage yield. [Mn = 55, S = 32, O = 16, H = 1]

(2 marks)

(4) In an experiment to prepare ethyl ethanoate, CH3COOC2H5, 23 g of ethanol, CH3CH2OH, produced 33 g of ethyl ethanoate. Calculate the percentage yield of the ethyl ethanoate. CH3COOH(l) + C2H5OH(l)  CH3COOC2H5(l) + H2O(l) [Molar masses/g mol–1: C2H5OH = 46, CH3COOC2H5 = 88]

(2 marks)

(5) Propan-2-ol, CH3CH(OH)CH3, can be dehydrated to produce propene. Calculate the atom economy for the production of propene by this method. CH3CH(OH)CH3  CH3CH=CH2 + H2O [Relative atomic masses: C = 12, H = 1, O = 16]

(2 marks)

(6) Propan-2-ol, CH3CH(OH)CH3, can be prepared by the hydrolysis of 2-bromobutane, CH3CH(Br)CH3, using aqueous sodium hydroxide solution. Calculate the atom economy for the production of propan-2-ol by this method. CH3CH(Br)CH3 + NaOH  CH3CH(OH)CH3 + NaBr [Relative atomic masses: C = 12, H = 1, O = 16, Br = 80]

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2.11 Continued

(7) Calculate the atom economy for the production of propan-2-ol by the hydration of propene, CH3CH=CH2. CH3CH=CH2 + H2O  CH3CH(OH)CH3 [Relative atomic masses: C = 12, H = 1, O = 16]

(1 mark)

(8) Explain one advantage to industry and one advantage to the environment of a process with a very high atom economy. (2 marks) Total: 15 marks