Amounts of substance in equations

This question is about monobasic acids and buffer solutions.

Nitric acid, HNO₃, is a strong monobasic acid.

Calculate the pH of 0.150 mol dm^–3 HNO₃.

Give your answer to 2 decimal places.

Nitrous acid, HNO₂, is a weak monobasic acid.

Predict whether the pH of 0.150 mol dm^–3 HNO₂ is higher, lower or the same as the pH of 0.150 mol dm^–3 nitric acid, HNO₃.

Explain your answer.

Prediction........

Explanation........

When heated, aqueous HNO₂ disproportionates. The equation is shown below.

• What is meant by disproportionation?

• Use oxidation numbers to show that disproportionation has taken place.

* A student plans to prepare a buffer solution with a pH of 4.85 using propanoic acid, CH₃CH₂COOH, and sodium propanoate, CH₃CH₂COONa.

K_a for CH₃CH₂COOH = 1.32 × 10^–5 mol dm^–3.

The student mixes 125 cm³ of 0.180 mol dm^–3 CH₃CH₂COOH(aq) with a calculated mass of CH₃CH₂COONa(s). The student assumes that the volume of the solution does not change.

• Calculate the mass of CH₃CH₂COONa needed to make 125 cm³ of a buffer solution with a pH of 4.85.

• Explain why this solution resists changes in pH when a small amount of alkali is added.

0.200 mol of HOOCCH₂CH₂COOH is reacted with 0.300 mol NaOH.

How many water molecules are formed?

A 1.204 × 10²³

B 1.806 × 10²³

C 2.408 × 10²³

D 3.612 × 10²³

This question is about different compounds that each contain O and H atoms covalently bonded together.

The alcohol 2,3‑dimethylhexan‑1‑ol has the molecular formula C₈H₁₈O.

Draw the skeletal formula of 2,3‑dimethylhexan‑1‑ol.

What is the number of H atoms in 8.45 g of 2,3‑dimethylhexan‑1‑ol?

Give your answer to 3 significant figures and in standard form.

Why does paracetamol not react with Na₂CO₃(aq)?

The student uses the reaction of nuromol tablets with Na₂CO₃(aq) to determine the mass of ibuprofen and the mass of paracetomol in one nuromol tablet.

The student’s method is outlined below.

• Weigh four nuromol tablets.

• Add the tablets to an excess of aqueous sodium carbonate.

• Collect the gas produced and measure its volume.

Results Mass of four nuromol tablets = 2.80 g Volume of gas collected at RTP = 48.0 cm³

Assume that ibuprofen is the only compound in nuromol tablets that reacts with Na₂CO₃(aq).

Determine the mass of ibuprofen and the mass of paracetomol, in mg, in one nuromol tablet.

Barium hydroxide, Ba(OH)₂, is an alkali. A student is supplied with a solution of Ba(OH)₂ with a concentration of 46.80 g dm^–3 at 25 °C.

The student dilutes 20.0 cm³ of this solution of Ba(OH)₂ with water and the solution is made up to 100.0 cm³ at 25 °C.

Calculate the pH of the diluted solution of Ba(OH)₂ at 25 °C.

Give your answer to 2 decimal places.

This question is about two metal hydrides, lithium aluminium hydride, LiAl H₄, and sodium borohydride, NaBH₄. Both hydrides are used as reducing agents in organic chemistry.

What is the systematic name of the alcohol C₆H₅CH₂OH?

Calculate the mass of LiAl H₄ that the student should use in Step 2 and the percentage yield of pure C₆H₅CH₂OH obtained in Step 4.

Give the mass of LiAl H₄ and the percentage yield of pure C₆H₅CH₂OH to 3 significant figures.

Percentage yield of pure C₆H₅CH₂OH =........ %

In the preparation, LiAl H₄ behaves as a nucleophile.

What is meant by the term nucleophile ?

The mechanism for Step 2 in the reduction of C₆H₅COOC₂H₅ is shown below. In the mechanism, LiAl H₄ can be represented as H^–.

Complete the mechanism by adding curly arrows to the three boxes.

Suggest why the student heated the mixture from Step 2 with dilute aqueous acid in Step 3.

NaBH₄ contains Na⁺ and BH₄^– ions.

Draw a ‘dot‑and‑cross’ diagram for NaBH₄.

Use a different symbol for the electrons from each element.

Show outer electrons only.

NaBH₄/ O₂ cells are being investigated as potential fuel cells.

• The positive electrode contains O₂.

• The negative electrode contains NaBH₄.

The reaction at the positive electrode and the overall cell reaction for a NaBH₄/ O₂ fuel cell are shown below.

Overall cell reaction: NaBH₄ + 2O₂ NaBO₂ + 2H₂O E = 1.64 V

What is the standard electrode potential of the negative electrode in this cell?

Construct the equation for the reaction at the negative electrode of this cell.

The equation for the reaction of sulfuric acid with potassium hydroxide is shown below.

25 cm³ of 1.00 mol dm^–3 H₂SO₄ is reacted with excess KOH. The energy given out is 2.8 kJ.

What is the enthalpy change of neutralisation, in kJ mol^–1?

A –56

B –70

C –112

D –224

Your answer

4.30 g of the alcohol C₅H₉OH, (M_r = 86.0), is burned in oxygen.

Which volume of oxygen gas is needed, in dm³, for this complete combustion of C₅H₉OH, at RTP?

A 1.2

B 2.4

C 5.8

D 8.4

1.35 g of ethylamine gas, CH₃CH₂NH₂ (M_r = 45.0), is reacted with 20 cm³ of 2.0 mol dm^–3 hydrochloric acid forming a solution of ethylammonium chloride.

What is the concentration of ethylammonium chloride in mol dm^–3?

A 0.03

B 0.67

C 1.50

D 2.00

This question is about different areas of chemistry.

Why do all average bond enthalpies have a positive value?

Determine the C–H bond enthalpy, in kJ mol^–1, using the information above.

C–H bond enthalpy =........ kJ mol^–1

Hydrogen gas is being considered as a household fuel to replace methane.

The enthalpy change of formation, _fH, for H₂O(l) is –285.8 kJ mol^–1.

Determine the energy released when 60.0 m³ of hydrogen is used as a household fuel at RTP.

Give your answer to 3 significant figures and in standard form.

Compound A is a chloride of a Period 3 element.

A student carries out the 2 steps below to find the formula of compound A.

Step 1 The student adds 5.00 10^–4 mol of compound A to water. A colourless solution is formed.

Step 2 The colourless solution reacts with exactly 60.0 cm³ of 2.50 10^–2 mol dm^–3 AgNO₃(aq) to form a white precipitate.

Write an ionic equation, with state symbols, for the reaction in Step 2.

Determine the formula of compound A.

Compound B, shown below, is an antiviral medicine.

What is the molecular formula of compound B ?

How many chiral carbon atoms are there in one molecule of compound B ?

Which sample contains the greatest number of molecules?

A 35.0 g of C₂H₂

B 45.0 g of C₂H₆

C 60.0 g of C₄H₁₀

D 100.0 g of C₆H₆

Your answer

How many hydrogen atoms are in 2.50 g of pharmacolite, CaHAsO₄•2H₂O (M_r = 216.0)?

A 6.97 10²¹

B 2.09 10²²

C 2.79 10²²

D 3.48 10²²

Your answer

40.0 cm³ of 0.200 mol dm^–3 HCl is added to 60.0 cm³ of 0.100 mol dm^–3 NaOH.

What is the concentration of the resulting solution?

A 0.0200 mol dm^–3 HCl and 0.0200 mol dm^–3 NaCl

B 0.0200 mol dm^–3 HCl and 0.0400 mol dm^–3 NaCl

C 0.0200 mol dm^–3 HCl and 0.0600 mol dm^–3 NaCl

D 0.0600 mol dm^–3 HCl and 0.0200 mol dm^–3 NaCl

Your answer

This question is about acids and bases.

Table 20.1 shows the ionic product, K_w, of water at 25 °C and 40 °C.

Table 20.1

Temperature /°C	Kw / mol2 dm–6
25	1.00 10−14
40	2.92 10−14

Calculate the pH of water at 40 °C.

Give your answer to 2 decimal places.

Table 20.1 shows different K_w values at 25 °C and at 40 °C. A student suggests that water is neutral at these temperatures.

Explain why this student is correct.

A student reacts strontium metal with water to make a 250.0 cm³ solution of aqueous strontium hydroxide, Sr(OH)₂. The solution contains 0.145 g of strontium hydroxide.

• Write an equation for the reaction of strontium with water.

• Calculate the pH of this 250.0 cm³ solution of strontium hydroxide at 40 °C. You should refer back to Table 20.1 at the start of (a).

Give your answer to 2 decimal places.

Equation........

Calculation

A student reacts 1.00 g of strontium carbonate, SrCO₃, with an excess of dilute nitric acid, HNO₃. A gas is produced.

Construct the equation for this reaction.

The student then reacts 1.00 g of calcium carbonate, CaCO₃, with an excess of dilute nitric acid, HNO₃.

Explain why the student’s two reactions produce different volumes of gas.

A student reacts an excess of magnesium with 25.0 cm³ of 0.500 mol dm^–3 hydrochloric acid, HC l.

The student also reacts an excess of magnesium with 25.0 cm³ of 0.500 mol dm^–3 ethanoic acid, CH₃COOH.

Construct an ionic equation for the reaction of magnesium with an acid.

Explain why these two reactions of magnesium produce the same volume of gas but at different rates.

Butanoic acid, CH₃CH₂CH₂COOH, is a weak monobasic acid.

Explain what is meant by the term monobasic acid.

A buffer solution is prepared by dissolving 3.39 g of potassium hydroxide in 250 cm³ of 0.376 mol dm^–3 butanoic acid.

This buffer solution has a pH of 5.07 at 25 °C.

Calculate the acid dissociation constant, K_a, of butanoic acid at 25 °C.

Assume that the volume of the solution remains constant at 250 cm³ when the potassium hydroxide is dissolved.

K_a =........ mol dm^–3

A buffer solution has a pH of 4.50.

When a small volume of water is added to this buffer solution, the pH does not change.

Explain why the pH does not change.

For complete combustion, 0.100 mol of an alkane requires 22.8 dm³ of O₂, measured at RTP.

Which alkane has undergone complete combustion?

A pentane

B hexane

C heptane

D octane

This question is about hydrocarbons.

The boiling points of some hydrocarbons containing 6 carbon atoms are shown below.

State and explain the trend in boiling points shown by these hydrocarbons.

2-methylpentane reacts with bromine by radical substitution.

A mixture of organic products is formed, including 3-bromo-2-methylpentane, and compounds A and B.

Complete the table below to show the mechanism for the formation of 3-bromo-2-methylpentane and three possible equations for termination.

In your equations, use structural or skeletal formulae and ‘dots’ (•) for the position of

Organic compound A is formed by the substitution of all 14 H atoms in 2-methylpentane by Br atoms.

Write the equation, using molecular formulae, for the formation of compound A from 2-methylpentane.

Organic compound B is formed by the substitution of some of the 14 H atoms in 2-methylpentane by Br atoms.

0.8649 g of compound B is heated until it is vaporised.

Under the conditions used:

• compound B has a volume of 72.0 cm³

• the molar gas volume is 40.0 dm³ mol^–1.

Determine a possible molecular formula of compound B.

This question is about aromatic compounds containing the –COOH and –OH functional groups.

Salicylic acid, shown below, is used in the manufacture of some important medicines.

Salicylic acid

Complete the flowchart for reactions of salicylic acid, by adding the organic products in each

PAS, shown below, is an antibiotic used to treat several diseases including tuberculosis (TB).

A student predicts that PAS could polymerise to form a polymer containing both ester and amide linkages.

Draw a section of this polymer.

The section should contain one amide and one ester linkage, which should be displayed.

For the treatment of TB, the maximum daily dosage of PAS that should be prescribed is 300 mg per kg of body mass.

A child weighs 20.0 kg.

Calculate the number of PAS molecules in the maximum daily dosage of PAS for this child.

Tutton’s salts are ‘double salts’ with the formula X₂Y(ZO₄)₂ • 6H₂O.

A Tutton’s salt contains two cations: X⁺ and Y²⁺.

• X + can be an ion of the Group 1 elements K, Rb, Cs or Fr, or an ammonium ion.

• Y²⁺ can be a 2+ ion of magnesium or an ion of most of the transition elements in Period 4.

• Z can be S or Cr.

(NH₄)₂Cu(SO₄)₂ • 6H₂O is an example of a Tutton’s salt.

Predict the formula of a Tutton’s salt containing different ions from (NH₄)₂Cu(SO₄)₂ • 6H₂O.

A student prepares a sample of the Tutton’s salt, (NH₄)₂Cu(SO₄)₂ • 6H₂O using the method shown below.

Step 1 Dissolve 0.025 mol of ammonium sulfate and 0.025 mol of hydrated copper(II) sulfate, CuSO₄ • 5H₂O, in water and make up to 50 cm³.

Step 2 Boil the resulting mixture for 2 minutes and allow to cool.

Step 3 Allow the solvent to evaporate slowly. Pale blue crystals of the Tutton’s salt form.

What masses are needed of ammonium sulfate and CuSO₄ • 5H₂O?

mass of ammonium sulfate........ g

mass of CuSO₄ • 5H₂O........ g

In Step 3, why does the student allow the solvent to evaporate and not boil off all the solvent in Step 2 ?

The student dissolves their Tutton’s salt in water. A pale blue solution forms.

The student carries out two tests on this aqueous solution.

The student adds an excess of aqueous ammonia to their aqueous solution of Tutton’s salt. A deep blue solution forms.

The complex ion responsible for the deep blue solution has a molar mass of 167.5 g mol^–1.

Suggest the formula of this complex ion.

The student adds NaOH(aq) to the aqueous solution of Tutton’s salt and warms the mixture.

A precipitate and a gas are formed.

Write the formulae of the precipitate and gas and suggest a test that could confirm the identity of the gas.

Formula of precipitate........

Formula of gas........

Test to confirm the identity of the gas........

How could the student carry out a test-tube test to confirm the anion in the Tutton’s salt?

This question is about nitric acid, hydrochloric acid and sulfuric acid.

Dilute nitric acid reacts with aluminium oxide to form a solution of aluminium nitrate.

Write an equation for this reaction.

The solution contains nitrate ions, NO₃^–.

Draw a ‘dot-and-cross’ diagram for the NO₃^– ion.

Use a different symbol for the extra electron.

Balance the half-equation for the oxidation process in this reaction.

In the reduction process in this reaction, HNO₃ and H⁺ react together to form 2 oxides: X (M_r = 30) and Z (M_r = 18).

Determine the formulae of X and Z and write the half-equation for this reduction.

* Three reactions involving sulfuric acid are shown below.

Reaction 1 Dilute sulfuric acid is reacted with nickel(II) hydroxide to form a green solution.

The solvent is allowed to evaporate leaving hydrated crystals of compound D, with the percentage composition by mass: Ni, 22.33%; S, 12.20%; O, 60.87%; H, 4.60%.

Reaction 2 Concentrated sulfuric acid is reacted with hydrogen bromide, HBr, to form three products:

• an element which exists as diatomic molecules

• a gaseous compound E

• a liquid.

At RTP, 1.00 dm³ of compound E has a mass of 2.67 g.

Reaction 3 Concentrated sulfuric acid acts as a catalyst when 2-hydroxypropanoic acid reacts to form compound F (M_r = 144).

In this reaction, 2 mol of 2-hydroxypropanoic acid forms 1 mol of compound F and 2 mol of water.

Identify compounds D, E and F and construct equations for the reactions.

Show structures for any organic compounds.

20 cm³ of nitrogen gas reacts with 10 cm³ of oxygen gas to form 20 cm³ of a gaseous product.

Which equation is the most likely for the reaction?

Your answer

0.541 g of an element X is reacted with oxygen to form 0.790 g of the oxide X₂O₃.

What is the element X ?

A A l

Your answer

This question is about energy changes.

Magnesium reacts with aqueous silver nitrate, AgNO₃(aq) as shown below.

A student adds an excess of magnesium to 100.0 cm³ of 0.400 mol dm^–3 AgNO₃(aq). The initial temperature is 20.0 °C.

Determine the maximum temperature reached in this reaction. Give your answer to 3 significant figures.

Assume that the specific heat capacity and density of the solution are the same as for water, and that there are no heat losses.

The student wants to repeat the experiment, but there is not enough AgNO₃(aq) left to use another 100.0 cm³ portion.

The student decides to modify the method by adding an excess of magnesium to 50.0 cm³ of 0.400 mol dm^–3 AgNO₃(aq).

Predict, with reasons, how this modification would affect the maximum temperature reached. Assume that there are no heat losses.

Nitric acid is manufactured from ammonia in a multi-stage process. The equation for the first stage in this process is shown in Reaction 17.1.

Some standard enthalpy changes of formation are shown in the table.

Compound	f H / kJ mol–1
NH3(g)	–46
H2O(l)	–286

Explain the term enthalpy change of formation.

Calculate the standard enthalpy change of formation, _fH, of NO(g).

_fH of NO(g) =........ kJ mol^–1

Carbon disulfide, CS₂, reacts with dinitrogen oxide, N₂O, as shown in Reaction 17.2.

Standard entropies, S, are shown in the table.

Substance	CS2(l)	N2O(g)	S8(s)	CO2(g)	N2(g)
S/ J K–1 mol–1	151	220	256	214	192

Explain the term entropy.

The free energy change, G, of Reaction 17.2 is –2672 kJ mol^–1 at 25 °C.

Calculate the enthalpy change, H, of Reaction 17.2, in kJ mol^–1.

H =........ kJ mol^–1

A student concludes that Reaction 17.2 is feasible at all temperatures.

Explain whether the student is correct or not.

This question is about the reactions of Group 2 metals and their compounds.

A student adds magnesium to dilute hydrochloric acid in one test tube. The student adds calcium to dilute hydrochloric acid in a second test tube.

A redox reaction takes place in each test tube.

Suggest two observations from the student’s experiment that would show that calcium is more reactive than magnesium.

Write half-equations for the reaction of magnesium with hydrochloric acid.

Oxidation half-equation:........

Reduction half-equation:........

A sample of barium oxide is added to distilled water at 25 °C. A colourless solution forms containing barium hydroxide, Ba(OH)₂.

The solution is made up to 250.0 cm³ with distilled water. The pH of this solution is 13.12.

Determine the mass of barium oxide that was used.

Give your answer to 3 significant figures.

10 cm³ of dilute sulfuric acid is added to 10 cm³ of the colourless solution of Ba(OH)₂

Write an ionic equation, including state symbols, for the reaction.

Limestone and huntite are two calcium minerals.

A typical sample of limestone contains 95.0% by mass of calcium carbonate, CaCO₃

Fertiliser Z, Ca₅NH₄(NO₃)₁₁•10H₂O (M_r = 1080.5 g mol^–1) can be made from limestone.

Calculate the mass, in g, of limestone needed to make 1.50 kg of fertiliser Z.

Give your answer to 3 significant figures.

Huntite is a carbonate mineral with the chemical formula Mg₃Ca(CO₃)₄.

Huntite reacts with dilute hydrochloric acid to produce bubbles of a gas and a colourless solution.

Construct the equation for the reaction. Include state symbols.

This question is about reactions of transition metal compounds.

Explain why ethane-1,2-diamine can act as a bidentate ligand.

The iron(III) ion, Fe³⁺, forms a complex ion A with two ethane-1,2-diamine ligands and two chloride ligands.

Complex ion A has cis and trans stereoisomers. One of these stereoisomers exists as optical isomers.

Determine the empirical formula, with charge, of complex ion A and draw the 3-D structures of the three stereoisomers.

Empirical formula with charge........

Structures

Aqueous sodium hydroxide is added to an aqueous solution of iron(II) sulfate. A pale green precipitate forms which turns brown when left to stand in air.

Write an ionic equation for the formation of the pale green precipitate.

* This question is about copper and copper compounds.

Experiment 1 Hydrochloric acid, HCl (aq), is added to an aqueous solution containing [Cu(H₂O)₆]²⁺ complex ions. A yellow-green solution forms containing complex ion B.

Experiment 2 A piece of copper metal is heated with concentrated sulfuric acid. A reaction takes place forming a pale blue solution C and 45 cm³ of a gas D, measured at RTP. The mass of gas D is 0.12 g.

Experiment 3 An excess of copper(II) oxide is heated with dilute nitric acid. The resulting mixture is filtered. The filtrate is a blue solution E. Aqueous potassium iodide, K I (aq), is added to the blue solution E. A white precipitate F and a brown solution G form.

Determine the formulae of B – G. Construct equations for the reactions taking place, include any changes in oxidation number,

and show your working where appropriate.

Complete combustion of 0.050 mol of an alkane produces 5.40 g of H₂O.

What is the molecular formula of the alkane?

A C₂H₆

B C₃H₈

C C₄H₁₀

D C₅H₁₂

The structure of the painkiller, paracetamol, is shown below.

A tablet contains 3.31 × 10^–3 mol of paracetamol.

What is the mass of paracetamol in the tablet?

A 493 mg

B 497 mg

C 500 mg

D 506 mg

This question is about redox reactions.

‘Calcium hypochlorite’, Ca(Cl O)₂, is an ionic compound used in ‘bleaching powder’.

The Cl O^– ion in Ca(Cl O)₂ is the active ingredient that kills bacteria.

Calcium hypochlorite is prepared by reacting chlorine gas with calcium hydroxide.

A student analyses the redox reactions shown below. State symbols have been omitted.

The student concludes that different ions containing chromium can act as oxidising or reducing agents.

Using the terms oxidising agent and reducing agent, and ideas about electrode potentials and equilibrium, explain how the student is correct.

Include overall equations.

A student bubbles hydrogen sulfide gas, H₂S(g), through an acidified solution containing manganate(VII) ions, MnO₄^–(aq).

A redox reaction takes place, forming aqueous manganese(II) ions, a yellow precipitate and one other product.

Construct the equation for this reaction. State symbols are not required.

This question is about energy changes.

* A student plans to determine the enthalpy change of hydration of calcium ions.

The student finds the information below from data tables.

The student carries out an experiment to find the enthalpy change of solution of calcium chloride.

Student’s method:

• Weigh a bottle containing calcium chloride and weigh a polystyrene cup.

• Add water from a measuring cylinder to the polystyrene cup and measure its temperature.

• Add the calcium chloride, stir the mixture, and measure the maximum temperature of the final solution.

• Weigh the empty bottle and weigh the polystyrene cup with the final solution.

Mass readings

Temperature readings

Calculate the enthalpy change of solution of calcium chloride and determine the enthalpy change of hydration of calcium ions.

Show your working, including an energy cycle linking the energy changes.

Assume that the density and specific heat capacity, c, of the solution are the same as for

water.

Internal combustion engines have historically used fuels obtained from crude oil as a source of power.

The environmental effects of fossil fuel use can be reduced by blending petrol with biofuels such as ethanol.

A fuel is being developed using a 1:1 molar ratio of octane and ethanol.

Write the equation for the complete combustion of this fuel.

Calculate the energy released, in kJ, by the complete combustion of 8.00 kg of this fuel.

_cH(C₈H₁₈) = –5470 kJ mol^–1; ∆_cH(C₂H₅OH) = –1367 kJ mol^–1.

Which sample contains the greatest number of molecules?

A 140.0 g C₂H₂

B 180.0 g C₂H₆

C 240.0 g C₄H₁₀

D 400.0 g C₆H₆

Your answer

Chromium(III) oxide, Cr₂O₃, is reduced to chromium by heating with magnesium.

What is the minimum mass of Mg required to reduce 11.4 g of chromium(III) oxide?

A 0.61 g

B 0.91 g

C 3.65 g

D 5.47 g

Your answer

A student is supplied with 100.0 cm³ of a solution of 0.400 mol dm^–3 magnesium iodide, MgI₂.

A student plans to dilute this solution so that the iodide concentration is 0.250 mol dm^–3.

What volume of water, in cm³, does the student need to add?

A 60.0

B 160.0

C 220.0

D 320.0

Your answer

This question is about acids, bases and buffers.

Sodium hydroxide, NaOH, is a strong base.

Calculate the pH of 0.140 mol dm^–3 NaOH(aq) at 298 K.

Give your answer to 2 decimal places.

Sulfuric acid reacts with sodium hydroxide as shown in Equation 22.1. Equation 22.1 H₂SO₄(aq) + 2NaOH(aq) → Na₂SO₄(aq) + 2H₂O(l) H₁ This is a neutralisation reaction.

A student carries out an experiment to determine the enthalpy change H₁ and uses this value to deduce the enthalpy change of neutralisation, _neutH.

The student measures out two solutions:

• 25.0 cm³ of 1.60 mol dm^–3 H₂SO₄(aq)

• 55.0 cm³ of 1.50 mol dm^–3 NaOH(aq) (an excess).

The temperature of each solution is the same.

The student mixes the two solutions. The temperature increases by 13.0 °C.

Show that NaOH is in excess.

Calculate the enthalpy change, H₁, for Equation 22.1, and deduce the value for the enthalpy change of neutralisation, ∆_neutH, in kJ mol^–1.

Assume that the densities of all solutions and the specific heat capacity, c, of the reaction mixture are the same as for water.

enthalpy change, H₁ =........ kJ mol^–1

enthalpy change of neutralisation, _neutH =........ kJ mol^–1

The student repeats the experiment using 50.0 cm³ of 1.60 mol dm^–3 H₂SO₄ and 110.0 cm³ of 1.50 mol dm^–3 NaOH.

Predict the increase in temperature.

Explain your reasoning.

* Nitrous acid, HNO₂, is a weak Brønsted–Lowry acid with a pK_a value of 3.34 at room temperature.

HNO₂ can be prepared by reacting N₂O₃ with water. HNO₂ is the only product.

A chemist makes up a buffer solution by the following method.

Step 1 The chemist weighs a sample of N₂O₃. Water is then added to form 100 cm³ of 0.500 mol dm^–3 HNO₂(aq).

Step 2 The chemist adds 100 cm³ of 0.150 mol dm^–3 NaOH(aq) to the 100 cm³ solution of 0.500 mol dm^–3 solution of HNO₂(aq). The resulting solution is made up to 1.00 dm³.

Explain why a buffer solution forms in Step 2. Determine the pH of this buffer solution and the mass of N₂O₃ that was used in Step 1.

Which sample contains the greatest number of carbon atoms?

A 20.0 g C₆H₅OH

B 30.0 g C₂H₅COOH

C 40.0 g CH₃CHO

D 50.0 g CH₃OH

This question is about organic acids.

Table 18.1 shows the R groups in four amino acids.

Most amino acids show optical isomerism.

Explain the term optical isomerism.

Draw 3-D diagrams to show the optical isomers of alanine.

How many optical isomers does threonine have?

Ibuprofen, shown below, is used as a painkiller.

What is the molecular formula of ibuprofen?

One ibuprofen tablet contains 400 mg of ibuprofen.

Calculate the number of ibuprofen molecules in one ibuprofen tablet.

Give your answer to 3 significant figures.

Tablets based on ibuprofen and lysine are now available from pharmacies.

These tablets are claimed to act faster than ibuprofen by being absorbed into the body more quickly than ibuprofen alone.

One type of these tablets contains a salt of ibuprofen and the amino acid lysine (R = –(CH₂)₄NH₂) in a 1:1 molar proportion.

Suggest why tablets based on a salt of ibuprofen should act faster in the body than ibuprofen.

This question is about organic compounds containing nitrogen.

Salt H, (CH₃)₂CHNH₃Cl, is used in the manufacture of garden weedkillers.

The flowchart shows the synthesis of the salt H from propanone.

Complete the flowchart. Show structures for organic compounds.

Aspartame, shown below, is an artificial sweetener commonly used as a sugar substitute.

Aspartame contains several functional groups.

Apart from the benzene ring, name the functional groups in aspartame.

A sample of aspartame is hydrolysed with aqueous acid.

Draw the structures of the three organic products of the complete acid hydrolysis aspartame.

A student carries out an investigation to identify two metals, M and X, by two different methods.

In Stage 1, a redox reaction takes place between M and HC l (aq), forming hydrogen and a solution containing M in the +2 oxidation state.

Write an overall equation, with state symbols, for this reaction. Write half-equations for the oxidation and reduction processes.

Overall equation........

Oxidation half-equation........

Reduction half-equation........

In Stage 1, suggest two observations that would confirm that all of metal M has reacted.

In Stage 3, write the ionic equation for the reaction taking place in the titration.

Metal M can be identified following the steps below.

1. The amount, in mol, of excess HC l (aq) that remains after the reaction of M with HC l (aq).

2. The amount, in mol, of HC l (aq) that reacted with M.

3. The identity of metal M.

Analyse the results to identify metal M.

The student is provided with the carbonate of an unknown metal, X₂CO₃.

The student measures the mass loss when the X₂CO₃ is reacted with an excess hydrochloric acid. The equation is shown below.

X₂CO₃(s) + 2HCl (aq) → 2XCl (aq) + CO₂(g) + H₂O(l)

The reaction is carried out using this method:

Step 1 Add 100 cm³ HCl (aq) to a conical flask and weigh.

Step 2 Add X₂CO₃ to the conical flask and immediately reweigh.

Step 3 After 5 minutes, reweigh the conical flask and contents.

Calculate the amount, in mol, of CO₂ released in the reaction.

After analysing the results, the student was told that their molar mass of X₂CO₃ was incorrect.

The student evaluated the experiment for possible reasons for the incorrect result.

The student wondered whether the reaction was complete when the mass was recorded after 5 minutes (Step 3).

How could the student modify the experimental procedure to be confident that the reaction was complete?

The student finds out that carbon dioxide is slightly soluble in water.

State and explain how the solubility of CO₂ would affect the calculated molar mass of X₂CO₃.

In the laboratory, acid spills can be cleaned up and made safe by spreading anhydrous sodium carbonate over the spill to neutralise the acid.

A student accidentally spills 50.0 cm³ of 2.00 mol dm⁻³ HCl (aq) on the bench.

What is the minimum mass of anhydrous sodium carbonate required to neutralise the acid?

A 4.15 g

B 5.30 g

C 8.30 g

D 10.6 g

Your answer

3.528 g of a Group 2 metal, M, is reacted with an excess of chlorine. The reaction forms 9.775 g of a chloride.

What is metal M ?

A magnesium

B calcium

C strontium

D barium

Your answer

Radical reactions are responsible for the catalysed breakdown of the ozone layer.

The overall equation is shown below.

The molar gas volume in the ozone layer is approximately 2.5 m³ mol⁻¹.

What is the energy released, in kJ, during the breakdown of 1.0 m³ of ozone in the ozone layer?

A 56.8

B 113.6

C 355

D 710

Your answer

This question is about reactions of ions and compounds of transition elements.

A student carries out two experiments on a solution containing [Cr(H₂O)₆]³⁺(aq).

Experiment 1 The student adds an excess of aqueous ammonia to a solution containing [Cr(H₂O)₆]³⁺ until a purple solution is formed.

Experiment 2 The student carries out the following reaction sequence.

Step 1 NaOH(aq) is added slowly to a solution containing [Cr(H₂O)₆]³⁺(aq) in a boiling tube. A grey–green precipitate forms.

Step 2 An excess of NaOH(aq) is added to the boiling tube. The precipitate dissolves and a green solution forms containing a 6 coordinate complex ion.

Step 3 H₂O₂ is added to the mixture and the boiling tube is heated. A yellow solution forms.

Step 4 The solution in the boiling tube is acidified. The solution now contains Cr₂O₇²⁻(aq).

What is the formula of the complex ion in the purple solution that forms in Experiment 1

Suggest an equation for the reaction in Experiment 2, Step 1. Include state symbols.

Draw a 3-D diagram for the shape of the complex ion that forms in Experiment 2, Step 2 Include the charge of the ion.

What is the formula of the ion that causes the yellow colour in Experiment 2, Step 3

State the colour of the solution that forms in Experiment 2, Step 4.

Vanadium ions have four common oxidation states. Table 18.1 shows the colours of the ions in aqueous solution.

Complete the electron configuration of a V³⁺ ion.

The student adds excess iron to a solution containing VO²⁺(aq) ions, and observes that the colour of the solution changes from blue to green and then to violet.

Use the relevant standard electrode potentials shown in Table 18.2 to explain these observations.

Construct an equation for the first colour change from blue to green.

Iron(II) gluconate, C₁₂H₂₂FeO₁₄, is the active ingredient in some brands of iron supplements.

A student carries out an experiment to determine the mass of iron(II) gluconate in one tablet of an iron supplement, using the method below.

Stage 1 The student crushes two tablets and dissolves the powdered tablets in dilute sulfuric acid.

Stage 2 The student makes up the solution from Stage 1 to 250.0 cm³ in a volumetric flask.

Stage 3 The student then titrates 25.0 cm³ portions of the solution obtained in Stage 2 with 0.00200 mol dm⁻³ potassium manganate(VII).

The student obtains a mean titre of 13.50 cm³.

In this titration, 1 mol of manganate(VII) ions reacts with 5 mol of iron(II) ions.

Explain why the student used 0.00200 mol dm⁻³ potassium manganate(VII) solution for this titration, rather than the more usual concentration of 0.0200 mol dm⁻³ used in manganate(VII) titrations.

Use the student’s results to determine the mass, in mg, of iron(II) gluconate in one tablet.

Give your answer to 3 significant figures.

This question is about weak acids.

The K_a values of three weak acids are shown in Table 20.1.

Calculate the pH of 0.0800 mol dm⁻³ C₂H₅COOH(aq).

Give your answer to 2 decimal places.

Show by calculation that 20.0 cm³ of NaOH(aq) is required to reach the end point.

Calculate the pH of the final solution.

Give your answer to 2 decimal places.

On the axes below, sketch a pH curve for the pH changes during the addition of 45.0 cm³ of 0.100 mol dm⁻³ NaOH(aq) to 25.0 cm³ of 0.0800 mol dm⁻³ C₂H₅COOH(aq).

The student considers using the four indicators in Table 20.2 for the titration.

Explain which indicator would be most suitable for the titration.

The student repeats the experiment starting with 25.0 cm³ of 0.0800 mol dm⁻³ HCN(aq) and adding a total of 45.0 cm³ of 0.100 mol dm⁻³ NaOH(aq).

Predict one similarity and one difference between the pH curve with C₂H₅COOH(aq) and the pH curve with HCN(aq). Use the information in Table 20.1, and your answer to (b)(iii).

Similarity........

Difference........

The student calculates the pH of 0.0800 mol dm⁻³ HIO₃(aq). The student assumes that the equilibrium concentration of HIO₃(aq) is the same as the initial concentration of HIO₃(aq).

The student measures the pH, and finds that the measured pH value is different from the calculated pH value.

Explain why the measured pH is different from the calculated pH.

These short questions are from different areas of chemistry.

Explain why a CF₄ molecule has polar bonds but does not have an overall dipole.

Explain why a small proportion of molecules in water have a relative molecular mass of 20.

What is the partial pressure of O₂ (in Pa) in a gas mixture containing 21% O₂ by volume and with a total pressure of 1.0 × 10⁵ Pa?

What mass of carbon dioxide (in g) is formed by the complete combustion of 42.0 m³ (measured at RTP) of propane?

What is the number of oxygen atoms in 4.26 g of P₂O₅?

This question is about reactions of iron compounds.

In the boxes, write the formulae of A and B.

The student thinks that the reaction of iron(II) sulfide with H⁺ / H₂O is a redox reaction.

Explain, with reasons, whether the student is correct.

Write the equation for the reaction of [Fe(H₂O)₆]²⁺(aq) with Cl₂(g).

Construct an equation for the reaction of H₂S(g) with H⁺(aq)/MnO₄⁻(aq).

This question is about acids and bases found in the home.

Ethanoic acid, CH₃COOH, is the acid present in vinegar.

A student carries out an experiment to determine the pK_a value of CH₃COOH.

• The concentration of CH₃COOH in the vinegar is 0.870 mol dm^–3.

• The pH of the vinegar is 2.41.

Write the expression for the acid dissociation constant, K_a, of CH₃COOH.

Calculate the pK_a value of CH₃COOH.

Give your answer to two decimal places.

Determine the percentage dissociation of ethanoic acid in the vinegar.

Give your answer to three significant figures.

Many solid drain cleaners are based on sodium hydroxide, NaOH.

• A student dissolves 1.26 g of a drain cleaner in water and makes up the solution to 100.0 cm³.

• The student measures the pH of this solution as 13.48.

Determine the percentage, by mass, of NaOH in the drain cleaner.

Give your answer to three significant figures.

Sodium carbonate, Na₂CO₃, is a base used in washing soda.

Na₂CO₃ contains the carbonate ion, CO₃^2–, shown below.

Draw the ‘ dot-and-cross ’ diagram for the carbonate ion.

Show outer electrons only and use different symbols for electrons from C and O, and any ‘extra’ electrons.

This question is about the hydrolysis of haloalkanes.

The rate of hydrolysis of a haloalkane depends on the halogen present.

State and explain how the halogen in the haloalkane affects the rate of hydrolysis.

A student hydrolyses a haloalkane, E, using the following method.

• 0.0100 mol of haloalkane E is refluxed with excess NaOH(aq) to form a reaction mixture containing an organic product F.

• The reaction mixture is neutralised with dilute nitric acid.

• Excess AgNO₃(aq) is added to the reaction mixture. 1.88 g of a precipitate G forms.

Organic product, F, has a molar mass of 74.0 g mol⁻¹ and has a chiral carbon atom.

Draw a labelled diagram to show how the student would carry out the hydrolysis of haloalkane E.

Analyse the information to identify E, F and G.

Show your working.

Select an element from the first three periods that fits each of the following descriptions.

The element that forms a 1– ion with the same electron configuration as helium.

The element with the highest first ionisation energy.

The element in Period 3 which has the successive ionisation energies shown below.

The element which forms a compound with fluorine that has octahedral molecules.

An element which reacts with water to form an acidic solution.

The element X, which forms a compound with hydrogen, XH₃, with a molar mass of 34.0 g mol^–1.

An element which forms a compound with hydrogen in which the element has an oxidation number of –4.

The element which has a density of 1.33 × 10^–3 g cm^–3 at room temperature and pressure.

Table 1.1 shows some properties of Period 3 chlorides.

Explain the properties shown in Table 1.1 in terms of bonding and structure.

This question looks at reactions of hydrogen peroxide and of cobalt(II) ions.

Aqueous hydrogen peroxide decomposes as shown in equation 2.1.

The reaction is catalysed by manganese(IV) oxide, MnO₂.

A student investigates the decomposition of a hydrogen peroxide solution as outlined below.

• The student adds 50.00 cm³ of H₂O₂(aq) to a conical flask.

• The student adds a small spatula measure of MnO₂ and quickly connects the flask to a gas syringe.

• The student measures the volume of oxygen every 200 seconds.

The student allows the reaction in equation 2.1 to proceed until no more gas is evolved. The volume of O₂ in the syringe is now 55 cm³, measured at RTP.

Calculate the initial concentration of the H₂O₂.

Give your answer to two significant figures.

initial concentration of H₂O₂ =........ mol dm^–3

Hydrogen peroxide can act as an oxidising agent or as a reducing agent.

Some standard electrode potentials are shown below.

Use this information to write an equation for a reaction in which hydrogen peroxide acts as a reducing agent.

Cobalt(II) forms complex ions with water ligands and with chloride ligands.

• With water ligands, cobalt(II) forms a pink octahedral complex ion, [Co(H₂O)₆]²⁺.

• With chloride ligands, cobalt(II) forms a blue tetrahedral complex ion.

A student dissolves cobalt(II) sulfate in water in a boiling tube. A pink solution forms.

Experiment 1 The student places the boiling tube in a water bath at 100 °C. Concentrated hydrochloric acid is added dropwise. The colour of the solution changes from pink to blue.

Experiment 2 The student places the boiling tube from experiment 1 in an ice/water bath at 0 °C. The colour of the solution changes from blue to pink.

Write the equilibrium equation for the reaction that takes place when the colour of the solution changes.

Explain the observations and predict whether the formation of the blue colour is exothermic or endothermic.

Complete combustion of an organic compound forms 40 cm³ of carbon dioxide and 40 cm³ water vapour, under the same conditions of temperature and pressure.

Which molecular formula could the organic compound have?

A C₃H₈

B C₂H₂O

C C₂H₄O

D C₂H₃N

0.1 mol of HOOCCH₂COOH are reacted with 0.1 mol of aqueous NaOH.

How many molecules of water are formed?

A 6.02 × 10²²

B 3.01 × 10²²

C 6.02 × 10²³

D 3.01 × 10²³

This question is about unsaturated hydrocarbons.

Compound A and compound B are isomers.

Compound A has a lower melting point than compound B.

Suggest why.

Compound C, CH₃CH₂CH=CHCH₂CH₂OH, exists as cis and trans stereoisomers.

Name compound C.

Define the term stereoisomers.

Draw the structures of the cis and trans stereoisomers of compound C.

The C=C group in an alkene contains a -bond.

Complete the diagram below to show how p-orbitals are involved in the formation of a -bond.

Compound D, shown below, reacts with hydrogen bromide by electrophilic addition. A mixture of two organic compounds, E and F, is formed.

compound D

Suggest how an HBr molecule can act as an electrophile.

Draw the structures of the two organic compounds E and F.

Outline the mechanism of the reaction between compound D and hydrogen bromide to form either compound E or compound F.

Include curly arrows and relevant dipoles.

Which of E or F is the major organic product?

Explain your answer.

Major organic product........

Explanation........

Myrcene, C₁₀H₁₆, is a naturally occurring hydrocarbon containing more than one carbon-carbon double bond.

Reaction of 204 mg of myrcene with hydrogen gas produces a saturated alkane.

Calculate the volume of hydrogen gas, in cm³ and measured at RTP, needed for this reaction.

Show your working.

-Carotene is a naturally occurring unsaturated hydrocarbon found in carrots. A -carotene molecule contains 40 carbon atoms, has two rings, and a branched chain.

0.0200 mol of -carotene reacts with 5.28 dm³ of hydrogen gas to form a saturated hydrocarbon.

Using molecular formulae, construct a balanced equation for this reaction.

Include relevant calculations and reasoning.

Equation........