Paddington Academy

Page 2

AS LEVEL CHEMISTRY

PAPER 1

PRACTICE PAPER 11

(structured questions only)

Answer all questions

Max 80 marks

Name..

Mark../80....%Grade

Note this paper only contains structured questions

1.Titanium(IV) oxide (TiO2, Mr = 79.9) is used as a white pigment in some paints. The pigment can be made as shown in the following equation.

TiCl4(l) + 2H2O(l) TiO2(s) + 4HCl(aq)

(a) (i) Calculate the percentage atom economy for the formation of TiO2

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(2)

(ii) In view of the low atom economy of this reaction, suggest how a company can maximise its profits without changing the reaction conditions or the production costs.

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(1)

(b) In an experiment 165 g of TiCl4 were added to an excess of water.

(i) Calculate the amount, in moles, of TiCl4 in 165 g.

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(2)

(ii) Calculate the maximum amount, in moles, of TiO2 which can be formed in this experiment.

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(1)

(iii) Calculate the maximum mass of TiO2 formed in this experiment.

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(1)

(iv) In this experiment only 63.0 g of TiO2 were produced. Calculate the percentage yield of TiO2

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(1)

(Total 8 marks)

2. Fluorine and iodine are elements in Group 7 of the Periodic Table.

(a) Explain why iodine has a higher melting point than fluorine.

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(2)

(b) (i) Draw the shape of the NHF2 molecule and the shape of the BF3 molecule.

Include any lone pairs of electrons that influence the shape. In each case name the shape.

Shape of NHF2 Shape of BF3

Name of shape of NHF2 .....................................................................

Name of shape of BF3 ........................................................................

(4)

(ii) Suggest a value for the FNF bond angle in NHF2

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(1)

(c) State the strongest type of intermolecular force in a sample of NHF2

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(1)

(d) A molecule of NHF2 reacts with a molecule of BF3 as shown in the following equation.

NHF2 + BF3 F2HNBF3

State the type of bond formed between the N atom and the B atom in F2HNBF3.

Explain how this bond is formed.

Name of type of bond ..................................................................................

How bond is formed .....................................................................................

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(2)

(Total 10 marks)

3.The following table shows the electronegativity values of the elements from lithium to fluorine.

Li

Be

B

C

N

O

F

Electronegativity

1.0

1.5

2.0

2.5

3.0

3.5

4.0

(a)(i)State the meaning of the term electronegativity.

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(2)

(ii)Suggest why the electronegativity of the elements increases from lithium to fluorine.

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(2)

(b) State the type of bonding in lithium fluoride.Explain why a lot of energy is needed to melt a sample of solid lithium fluoride.

Bonding .........................................................................................................

Explanation ....................................................................................................

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(3)

(c) Deduce why the bonding in nitrogen oxide is covalent rather than ionic.

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(1)

(d) Oxygen forms several different compounds with fluorine.

(i)Suggest the type of crystal shown by OF2

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(1)

(ii)Write an equation to show how OF2 reacts with steam to form oxygen and hydrogen fluoride.

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(1)

(iii)One of these compounds of oxygen and fluorine has a relative molecular mass of 70.0 and contains 54.3% by mass of fluorine.

Calculate the empirical formula and the molecular formula of this compound.Show your working.

Empirical formula .................................................................................

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Molecular formula .................................................................................

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(4)

(Total 14 marks)

4.The following dynamic equilibrium was established at temperature T in a closed container.

P(g) + 2Q(g) 2R(g) H = 50 kJ mol1

The value of Kc for the reaction was 68.0 mol1 dm3 when the equilibrium mixture contained 3.82 mol of P and 5.24 mol of R.

(a) Give the meaning of the term dynamic equilibrium.

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(2)

(b) Write an expression for Kc for this reaction.

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(1)

(c) The volume of the container was 10.0 dm3.

Calculate the concentration, in mol dm3, of Q in the equilibrium mixture.

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(4)

(d) State the effect, if any, on the equilibrium amount of P of increasing the temperature.All other factors are unchanged.

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(1)

(e) State the effect, if any, on the equilibrium amount of P of using a container of larger volume. All other factors are unchanged.

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(1)

(f) State the effect, if any, on the value of Kc of increasing the temperature.All other factors are unchanged.

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(1)

(g) State the effect, if any, on the value of Kc of using a container of larger volume.All other factors are unchanged.

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(1)

(h) Deduce the value of the equilibrium constant, at temperature T, for the reaction

2R(g) P(g) + 2Q(g)

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(1)

(Total 12 marks)

5.This question is about Group 7 chemistry.

(a) Sea water is a major source of iodine.The iodine extracted from sea water is impure. It is purified in a two-stage process.

Stage 1

l2+2H2O+SO22Hl+H2SO4

Stage 2

2Hl+Cl2l2+2HCl

(i)State the initial oxidation state and the final oxidation state of sulfur in Stage 1.

Oxidation state of S in SO2 ....................................................................

Oxidation state of S in H2SO4 ................................................................

(2)

(ii)State, in terms of electrons, what has happened to chlorine in Stage 2.

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(1)

(b) When concentrated sulfuric acid is added to potassium iodide, iodine is formed in the following redox equations.

......KI+......H2SO4......KHSO4+......l2+S+......H2O

8KI+9H2SO48KHSO4+4l2+H2S+4H2O

(i)Balance the equation for the reaction that forms sulfur.

(1)

(ii)Deduce the half-equation for the formation of iodine from iodide ions.

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(1)

(iii) Deduce the half-equation for the formation of hydrogen sulfide from concentrated sulfuric acid.

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(1)

(c) A yellow precipitate is formed when silver nitrate solution, acidified with dilute nitric acid, is added to an aqueous solution containing iodide ions.

(i)Write the simplest ionic equation for the formation of the yellow precipitate.

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(1)

(ii)State what is observed when concentrated ammonia solution is added to this yellow precipitate.

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(1)

(iii) State why the silver nitrate solution is acidified when testing for iodide ions.

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(1)

(iv) Explain why dilute hydrochloric acid is not used to acidify the silver nitrate solution in this test for iodide ions.

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(1)

(d) Chlorine is toxic to humans. This toxicity does not prevent the large-scale use of chlorine in water treatment.

(i)Give one reason why water is treated with chlorine.

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(1)

(ii)Explain why the toxicity of chlorine does not prevent this use.

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(1)

(iii) Write an equation for the reaction of chlorine with cold water.

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(1)

(e) Give the formulas of the two different chlorine-containing compounds that are formed when chlorine reacts with cold, dilute, aqueous sodium hydroxide.

Formula 1 .....................................................................................................

Formula 2 .....................................................................................................

(1)

(Total 14 marks)

6.Some antacid tablets contain sodium hydrogencarbonate, sucrose and citric acid.

(a) Analysis of a pure sample of citric acid showed that it contained 37.50% of carbon and 4.17% of hydrogen by mass, the remainder being oxygen. Use these data to show that the empirical formula of the acid is C6H8O7.

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(3)

(b) When the antacid tablet is added to water, sodium hydrogencarbonate and citric acid react together to form a gas. Identify this gas.

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(1)

(c) A weighed portion of this antacid was added to water. The gas formed was collected and its volume measured.

(i)Draw a diagram to show how this experiment could have been carried out to collect and measure the volume of the gas.

(ii)The experiment was repeated with further weighed portions of the same antacid.

The results are shown below.

Experiment

1

2

3

4

5

Mass of antacid / g

2.60

1.17

0.88

2.31

1.80

Volume of gas collected / cm3

168

86

57

149

116

On the graph paper below, plot a graph of mass of antacid (x-axis) against volume of gas collected.

(3)

Draw a line of best fit on the graph, ignoring any anomalous points.

(1)

Use the graph to determine the volume of gas which would have been collected using 2.00 g of antacid.

Volume of gas collected .......................................

(1)

(d) Suggest one reason why the presence of sodium hydrogencarbonate in the stomach may cause a person to suffer some extra discomfort for a short time.

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(1)

(e) Explain why the value for the Mr of citric acid does not need to be an exact value to deduce the molecular formula of citric acid from its empirical formula.

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(2)

(f) Apart from misreading the gas volume, suggest two reasons why the volumes of gas collected may be lower than the volumes of gas produced.

Reason 1 .......................................................................................................

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Reason 2 .......................................................................................................

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(2)

(g) Explain why it is important to record the temperature and pressure when measuring the volume of a gas.

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(1)

(h) Suggest why, in an analysis of an antacid, it is important to test samples from more than one bottle of the antacid.

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(1)

(i) In the industrial production of sodium hydrogencarbonate, ammonia and carbon dioxide are bubbled through a saturated solution of sodium chloride. The equation for this reaction, and some solubility data, are shown below.

NaCl(aq)+NH3(aq)+CO2(g)+H2O(l)NaHCO3(s)+NH4Cl(aq)

Compound

Solubility in water at 20 C / g dm3

sodium chloride

360

sodium hydrogencarbonate

96

ammonium chloride

370

(i)Suggest one reason why sodium hydrogencarbonate precipitates from the reaction mixture at this temperature.

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(1)

(ii)Explain how this reaction could be used to remove carbon dioxide from the gases formed when fossil fuels are burned.

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(1)

(j) The thermal decomposition of sodium hydrogencarbonate produces sodium carbonate. The other products are water and carbon dioxide. Write an equation for this thermal decomposition.

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(1)

(k) Sodium carbonate is produced on an industrial scale by a multi-step process. The equation which summarises the reactions taking place is shown below.

CaCO3+2NaClCaCl2 + Na2CO3

Calculate the percentage atom economy for the production of sodium carbonate by this reaction.

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(1)

(Total 20 marks)