AQA A Level Chemistry

Topic Questions

4.1 Physical Chemistry Practicals

1a3 marks

Name the pieces of equipment shown in Figure 1.

Figure 1

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1b3 marks

You are required to prepare 250 cm3 of a 0.100 mol dm-3 solution of copper sulfate, CuSO4.

i)
Calculate the number of moles of CuSO4 needed for the solution.

ii)
Calculate the molar mass of CuSO4.

iii)

Calculate the mass of CuSO4 required to prepare 250 cm3 of a 0.100 mol dm-3 copper sulfate solution.

1c2 marks

Distilled water is used to make up aqueous standard solutions.

Identify two pieces of equipment that should be rinsed with distilled water when making a standard solution.

1d2 marks

A standard solution of 0.50 mol dm-3 sodium carbonate (Mr = 106 g mol-1) is made using the following method.

  1. Weigh out 50.3 g of sodium carbonate into a weighing boat.
  2. Transfer the sodium carbonate into a beaker.
  3. Rinse the weighing boat, with distilled water, into the beaker.
  4. Add approximately 50 cm3 of distilled water to the beaker.
  5. Stir the beaker.
  6. Transfer the solution from the beaker into a 1 dm3 volumetric flask.
  7. Rinse the beaker, with distilled water, into the volumetric flask.
  8. Add distilled water to the volumetric flask until the bottom of the meniscus is level with the graduation mark.
  9. Stopper the volumetric flask and invert.
  10. Remove the stopper and check the bottom of the meniscus is level with the graduation mark.
  11. If necessary, add distilled water to bring the bottom of the meniscus to the graduation mark.

i)
Identify an improvement that can be made to Step 7 to ensure that as much sodium carbonate is transferred to the volumetric flask as possible.

ii)

Use the information in this question, to state the amount of sodium carbonate and distilled water required to make a 0.25 mol dm-3 sodium carbonate solution.

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2a2 marks

The key piece of equipment in a titration experiment is the burette.

A student sets a burette up as shown in Figure 1. The student writes down an initial volume of 0.0 cm3 in their results table before starting the titration.

Figure 1

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Identify two errors with the student’s set up of the burette.

2b2 marks

Phenolphthalein is colourless in acidic and neutral conditions but pink / purple in basic conditions.

It is a common indicator for the titration of sodium hydroxide with hydrochloric acid.

i)
State why an indicator is required for the titration of sodium hydroxide with hydrochloric acid.

ii)
Suggest why phenolphthalein is a better indicator than universal indicator solution for the titration of sodium hydroxide with hydrochloric acid.
2c3 marks

A titration experiment for the reaction of sodium hydroxide and hydrochloric acid was performed and the titration results are shown in Table 1.

Table 1

 

Rough

Run 1

Run 2

Run 3

Initial burette reading / cm3

0.00

0.00

24.30

0.05

Final burette reading / cm3

25.15

24.30

48.65

24.15

Titre volume / cm3

25.15

 

24.35

 

Concordant results

 

 

 

 

i)
Complete the titre volume results for Run 1 and Run 3 in Table 1.

ii)
Identify the two concordant results by placing a tick in the relevant box in Table 1.

iii)
Calculate the average titre, using the concordant results from part (ii).
2d3 marks

A student carried out a titration with sodium hydroxide solution to determine the mass of the acid in the solution. The student repeated the titration until concordant titres were obtained.

H2C2O4 (aq) + 2NaOH (aq) ⟶ Na2C2O4 (aq) + 2H2O (l)

A titration was carried out with sodium hydroxide to determine the unknown concentration of hydrochloric acid in a container.

NaOH + HCl → NaCl + H2O

It was found that 25.0 cm3 of the hydrochloric acid required an average titre of 22.50 cm3 of 0.100 mol dm-3 sodium hydroxide solution.

i)
Calculate the number of moles of sodium hydroxide.

ii)
Deduce the number of moles of hydrochloric acid.

iii)
Calculate the concentration of the hydrochloric acid.

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3a1 mark

The equipment set up in Figure 1 is used to measure the enthalpy change for a reaction.

Figure 1

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Suggest why a polystyrene cup is used for this experiment.

3b4 marks

25.0 cm3 of hydrochloric acid is added to the polystyrene cup. The temperature is taken every minute for 3 minutes. On the fourth minute, 25.0 cm3 of sodium hydroxide is added. The temperature of the reaction mixture is then recorded every minute for a further 7 minutes. The results are shown in Figure 2.

Figure 2

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i)
Draw a straight line of best fit through the first four points and extend it past the fourth minute.

ii)
Circle the anomalous result.

iii)
Draw an appropriate line of best fit through the last seven points and extend it back past the fourth minute.

iv)

Draw a dotted line labelled ?T to show the temperature change occurring at the fourth minute.

3c3 marks

The results in part (b) are used in the calorimetry calculation to determine the energy of the reaction.

Q = mc?T

i)
Use the information in part (a) to identify a value for the mass, m, to be used in the equation.

ii)
Use the information in part (b) to identify a value for the temperature change, ?T, for this reaction.

iii)
The units of specific heat capacity, c, are  J K-1 g-1. State the units of Q.
3d1 mark

A similar experimental set up to part (a) is shown in Figure 3. This equipment can be used to determine the enthalpy of combustion of a fuel.

Figure 3

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Define standard enthalpy of combustion.

3e4 marks

0.61 g of ethanol (Mr = 46.0 g mol-1) was burned in a spirit burner and used to heat 100 cm3 of water in a copper calorimeter. The temperature of the water rose by 40 degreeC.

i)
Calculate the energy change, in joules, for this reaction. Assume that the specific heat capacity of the reaction mixture is 4.18 J K-1 g-1.

ii)
Convert your answer to part (i) into kilojoules.

iii)
Calculate the number of moles of ethanol burned.

iv)
Calculate the enthalpy of combustion of ethanol using your answers to parts (ii) and (iii).

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4a3 marks

The skeletal formula of succinic acid is shown in Figure 1.

Figure 1

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i)
State the IUPAC name for succinic acid.

ii)
Give the molecular formula of succinic acid.

iii)
Calculate the molar mass of succinic acid.
4b4 marks

Name the types of reaction given in the following chemical equations.

i)
HOOCCH2CH2COOH + 2 NaOH → NaOOCCH2CH2COONa + 2 H2O

ii)
MgSO4 + 7 H2O → MgSO4.7H2O

iii)
CuSO4 + Zn → ZnSO4 + Cu

iv)
2 NaHCO3 → 2 Na2CO3 + CO2 + H2O
4c1 mark

Write the balanced symbol equation, including state symbols, for the complete combustion of butan-2-ol.

4d1 mark

Write the Kc expression for the esterification reaction between ethanoic acid and ethanol to form ethyl ethanoate and water.

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5a2 marks

In the school laboratory, there are three factors that can easily be altered when investigating the reaction between calcium carbonate and hydrochloric acid.

Identify two of the factors that can easily be altered in the school laboratory.

5b1 mark

In the reaction between sodium thiosulfate and hydrochloric acid, a black cross is often placed underneath the reaction vessel.

Na2S2O3 (aq) + 2 HCl (aq) → 2 NaCl (aq) + H2O (l) + SO2 (g) + S (s)

Identify the product that is responsible for the black cross disappearing from view.

5c2 marks

Identify two factors affecting the rate of reaction, that are commonly investigated using the sodium thiosulfate and hydrochloric acid reaction.

5d1 mark

When investigating the effect of concentration on the rate of a chemical reaction, it is common to plot a graph of concentration (x-axis) against time (y-axis).

When investigating the effect of temperature on the rate of a chemical reaction, it is common to plot a graph of temperature (x-axis) against rate (y-axis).

State the mathematical relationship between time and rate.

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1a4 marks

Compounds A to F, as shown in Figure 1, are a 50 : 50 mixture of polar and nonpolar covalent molecules.

Figure 1

15

Table 1 shows the electronegativity values for some elements.

Table 1

Element

Electronegativity / eV

Bromine

2.96

Carbon

2.55

Hydrogen

2.20

Iodine

2.66

Oxygen

3.44

Phosphorus

2.19

Sulfur

2.58

Use the information to suggest a maximum value for the difference in electronegativity which allows a covalent molecule to be classified as nonpolar. Justify your answer.

Give your answer to 2 decimal places.

1b4 marks

The displayed formulae for methane, dibromomethane and tetrabromomethane are shown in Figure 2.

Figure 2

16

A student concluded that all three compounds were nonpolar because they are symmetrical.

Use your knowledge of structure and bonding to evaluate the student’s conclusion.

1c3 marks

Student 1 suggests that compounds B and D, from Figure 1, are nonpolar molecules; student 2 suggests that they are polar.

Explain how both students could be considered to be correct. You may draw Lewis structures with partial charges to illustrate your explanation.

1d6 marks

Cyclohexane, ethanol, propanone and water are placed in separate burettes.

Each liquid is tested by opening the burette to provide a steady stream of the liquid. A woolen cloth is used to transfer electrons to a plastic ruler. The ruler is then held near the stream of liquid, as shown in Figure 3, to see the deflection, if any, that the charged plastic ruler causes to the stream of liquid.

Figure 3

17

Place the four liquids in order from 1 - the least to 4 - the most deflected. Use information from Table 1 in part (a) to help explain your order.

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2a3 marks

A student is set the challenge of creating a sodium hydroxide solution with a concentration of exactly 0.12 mol dm-3 using limited chemical resources. They do have access to any glassware that they require.

The chemical resources available to the student are:

  • Approximately 0.21 mol dm-3 sodium hydroxide solution
  • 15 mol dm-3 nitric acid
  • Phenolphthalein

The student sets up a titration experiment as shown in Figure 1.

Figure 1

18

The student completes a rough titration, as shown in Figure 1 and records a value of 36.20 cm3. They then refill the burette with nitric acid.

State the errors the student has made and explain their effects on the titre values.

2b4 marks

The student determines that the actual concentration of the sodium hydroxide solution is 97.57% of the approximate concentration.

One of the two concordant results that the student uses for their titration calculation is 34.20 cm3.

Use the information in part (a) to determine the volume of the student’s other concordant result. Show your working.

2c2 marks

The student wants to convert 100 cm3 of a 0.18 mol dm-3 sodium hydroxide solution into a 0.12 mol dm-3 sodium hydroxide solution.

Calculate the volume of water that they need to add.

2d2 marks

Another student suggests that an alternative method to make the 0.12 mol dm-3 solution is to evaporate the water from the original, approximately 0.21 mol dm-3 solution.

Once the sodium hydroxide has been recovered from the original solution, then the required mass of sodium hydroxide to make a 0.12 mol dm--3 solution can be weighed out and dissolved in a standard flask.

Explain how the hygroscopic nature of sodium hydroxide could affect the final concentration of the solution.

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3a4 marks

The reaction between sodium thiosulfate solution and hydrochloric acid is commonly investigated by measuring the time taken for a cross placed underneath the reaction mixture to disappear, as shown in Figure 1.

Figure 1

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i)
Write a balanced symbol equation, including state symbols for the reaction between sodium thiosulfate and hydrochloric acid.

ii)

Identify two chemical hazards for this reaction and state two control measures that can be implemented to reduce these hazards when investigating the effect of temperature. You do not need to discuss the use of personal protective equipment or fume cupboards.

3b5 marks

A student completes an investigation into the effect of temperature on the rate of reaction for sodium thiosulfate with hydrochloric acid. Their results are shown in Table 1.

Table 1

Temperature / degreeC

18.0

26.0

29.0

34.0

41.0

46.0

54.0

Time / s

100

60

49

36

25

18

12

Reaction rate / s-1

 

 

 

 

 

 

 

Plot a graph of reaction rate against temperature on Figure 2.

Figure 2

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3c2 marks

Use your knowledge of Maxwell-Boltzmann distribution curves to explain the effect of temperature on the reaction between sodium thiosulfate and hydrochloric acid, as shown in your answer to part (b).

3d2 marks

A student suggests that the initial rate of the reaction between sodium thiosulfate and hydrochloric acid could be measured by collecting the sulfur dioxide produced in a 250 cm3 gas syringe.

The student’s suggested method is as follows:

  1. Place 100 cm3 of 0.05 mol dm-3 of sodium thiosulfate solution into a conical flask
  2. Add 10 cm3 of 3.0 mol dm-3 hydrochloric acid into the conical flask
  3. Connect the conical flask to the gas syringe with a delivery tube and start the timer
  4. Record the volume of gas produced every 30 seconds until the volume of gas has remained constant for 2 minutes
  5. Plot and use a graph of the results to estimate the initial rate of reaction

Using your equation from part (a), justify whether or not this method would be effective in producing valid results in a school laboratory.

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4a2 marks

An experiment is set up, as shown in Figure 1, to determine the formula of an unknown sample of hydrated copper sulfate, CuSO4.xH2O.

Figure 1

21

The hydrated copper sulfate is carefully heated, until constant mass, to drive off the water of crystallisation. The water is then condensed in a test tube held in a beaker of ice water.

Explain why the mass of water in the test tube cannot be relied upon to determine the mass of water for a water of crystallization calculation.

4b2 marks

An 8.0 g sample of the hydrated copper sulfate is heated to constant mass, using the equipment shown in part (a).

Student A predicts that the formula of the hydrated copper sulfate will be CuSO4.5H2O.

Student B predicts that the hydrated copper sulfate will contain 7 waters of crystallisation.

Calculate the constant mass that each student would expect to see to prove their prediction.

4c6 marks

When the 8.0 g of hydrated copper sulfate is heated, it achieves a constant mass of 4.77 g. Both students from part (b) observe thin white fumes from the top of the test tube while the water of crystallisation is condensing.

Suggest a formula for the hydrated copper sulfate and explain which student is likely to be correct in their prediction.

4d3 marks

The reaction scheme for the formation of hydrated copper sulfate from its anhydrous form is shown in Figure 2.

Figure 2

22

i)
Use the reaction scheme, the data provided in Table 1 and Hess’s Law to calculate the enthalpy of hydration for anhydrous copper sulfate.
Table 1

 

ΔH / kJ mol-1

Solution enthalpy for CuSO4 (s)

- 66.1

Solution enthalpy for CuSO4.5H2O (s)

+ 11.0

Hydration enthalpy for CuSO4 (s)

To be calculated



ii)
Use your answer to part (i) to explain why this cannot be measured directly.

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5a2 marks

Ethanoic acid and ethanol can undergo a condensation reaction to form ethyl ethanoate and water according to the following equation.

CH3COOH + C2H5OH ⇋ CH3COOC2H5 + H2O

12.0 g of ethanoic acid and 11.5 g of ethanol were mixed in a stoppered bottle. The reaction mixture was left to reach equilibrium at room temperature. The mixture was then poured into a volumetric flask and made up to a total volume of 250 cm3.

A 25.0 cm3 sample of the resulting mixture required 26.5 cm3 of 0.200 mol dm-3 sodium hydroxide to neutralise the remaining ethanoic acid.

Calculate the number of moles of ethanoic acid in the reaction mixture at equilibrium.

5b6 marks

Use the information in part (a) to calculate a value for KC for the reaction, including units.

Give your answer to the appropriate number of significant figures.

5c3 marks

The reversible reaction of ethanol with ethanoic acid is exothermic in the forward direction. Explain the effect that an increase in temperature will have on the value of KC.

5d6 marks

There is an equilibrium between chemicals X and Y is as shown:

X ⇋ Y

At 100 degreeC, the value of KC for the reaction is 39. At the start of the reaction there are 2.0 moles of X. Calculate the number of moles of X at equilibrium.

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1a6 marks

Iron is extracted from iron (III) oxide in the Blast Furnace by reducing it with carbon. However, the iron which is extracted is still impure. It contains small amounts of carbon which can be removed by blowing oxygen through the impure iron.

To analyse the purity of the molten iron, a redox titration can be carried out. A sample of the iron is reacted with dilute hydrochloric acid, to form iron (II) chloride and a gas.

A sample of the formed solution is then reacted with potassium manganate (VII).

i)
State how the carbon impurities are removed when oxygen is blown through the impure iron. Include a reaction equation in your answer.

ii)
Give the equation for the reaction of iron with an excess of dilute hydrochloric acid.
Include state symbols in your answer.

iii)

Give the full redox equation for the reaction of the iron (II) ions with the manganate (VII) ions in acidic solution.

1b2 marks

The following steps were carried out to analyse the amount of carbon impurities present in the extracted iron.

Step 1 - Take samples of the iron at different stages of the process

Step 2 - React the samples of impure iron that have been collected with an excess of dilute hydrochloric acid to form iron (II) chloride solution.

Step 3 - Make up each solution to 100 cm3.

Step 4 - From each 100 cm3 sample solution which is made, take a 50.0 cm3 portion of and reacts it with a solution of potassium manganate (VII).

i)
Suggest one way to improve to the method above to ensure that the results from the experiments can be trusted.

ii)
How does your suggestion (i) improve the results of the experiment?
1c7 marks

At one stage of the analysis, a 1.39 g sample of impure iron was reacted with an excess of dilute hydrochloric acid and the solution was made up to 100 cm3.

A 50.0 cm3 portion of this solution was reacted with 21.7 cm3 of a 0.0962 mol dm-3 solution of potassium manganate (VII).

i)

Calculate the mass of carbon impurity present in the 1.39 g of sample (assume that carbon is the only impurity present).    Give your answer to the appropriate number of significant figures.

ii)
Calculate the percentage by mass of carbon in the sample.
1d2 marks

Using your answers to part (c) suggest whether the scientist should stop blowing oxygen at this stage. Explain your answer.

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2a5 marks

The reaction of calcium carbonate with dilute hydrochloric acid results in the formation of a gas.

The effect of increasing the concentration of the acid on the rate of reaction can be determined by measuring the amount of gas produced at regular intervals for several minutes.

i)
Give the equation for the reaction of calcium carbonate with dilute hydrochloric acid.
Include state symbols.

ii)
State an experimental condition that should remain constant during this experiment.

iii)

Explain what effect an increase in this condition stated in (ii) would have on the rate of the reaction.

2b6 marks

The following method was used to measure the rate of the reaction of CaCO3 with HCl:

Step 1 - Support a gas syringe with a stand, boss and clamp

Step 2 - Measure 50 cm3 of 0.050 mol dm-3 dilute HCl in a beaker and then add it to a conical flask

Step 3 - Add about 2.5 g of CaCO3 to the flask using a spatula, immediately connect the gas syringe and start counting.

Step 4 - Record the volume of gas produced every 20 seconds for 2 minutes.

Step 5 - Repeat Steps 1-4 for different concentrations of HCl.

i)
Suggest two improvements to the method used.

ii)
Complete the missing hazards, risk and precautions in Table 1 below.

Table 1

Hazard

Risk

Precaution

 

Causes skin and eye irritation

 

Effervescence in the reaction mixture

 

Use a large conical flask;
Do not look over the top when adding the CaCO3;
Use eye protection; wear gloves

iii)

How can you tell that the reaction is complete?

2c4 marks

The results for the reaction of 2.5 g of CaCO3 with 50 cm3 of 0.050 mol dm-3 dilute HCl were recorded in Table 2 below.

Table 2

Time (s)

0.00

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

110.0

120.0

Volume of CO2 (cm3)

0.00

4.80

9.10

12.3

16.0

20.2

23.7

26.4

28.2

28.9

29.1

29.1

29.2


Using the results given in the table, plot a graph of time (s) on the x-axis and volume of CO2 (cm3) on the y-axis. Draw a line of best fit on the graph.

Figure 1

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2d3 marks

Use the results and your graph from part (c) to calculate the initial rate of reaction. Give your answer to 2 decimal places and state the correct units.

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3a4 marks

The enthalpy of combustion of an unknown liquid fuel can be determined by carrying out a calorimetry experiment.

i)
Draw a labelled diagram of the apparatus set-up required to carry out such an experiment.

ii)
State one way to reduce uncertainties in this experiment.
3b2 marks

A student used the following method to carry out the experiment.

Step 1 - Measure 100 cm3 of water into a calorimeter using a measuring cylinder.

Step 2 - Record the initial temperature of the water using a thermometer.

Step 3 - Heat the water using the flame from the burning fuel and record the final temperature.

Step 4 - Measure the final mass of the spirit burner with the liquid fuel.

i)
Which crucial step in the calorimetry experiment has been left out in the method above?

ii)
Why is the step mentioned in part (i) important?
3c5 marks

The student obtained the following results:

  • Mass of water in calorimeter = 350 g
  • Initial temperature of water = 9 degreeC
  • Final temperature of water = 36 degreeC
  • Mass of liquid fuel burned = 3.15 g
i)

Calculate the amount of energy required to raise the temperature of the water from its initial to its final temperature (c = 4.2 J g-1 K-1). Give your answer to three significant figures.

ii)
Calculate the amount of liquid fuel burned in moles (Mr of the liquid fuel is 63.2 g mol-1). Give your answers to two significant figures.

iii)

Use your answer to part (i) and (ii) to calculate the enthalpy of combustion of 1.0 mol of the liquid fuel. Give your answer to three significant figures and state the correct units.

3d2 marks

The actual value of ΔHc of the unknown liquid is greater than the value calculated in part (c). Give two reasons for this.

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4a4 marks

Lactic acid is a chemical byproduct of anaerobic respiration, with the chemical formula C3H6O3. Bacteria in yoghurt will produce it, as will bacteria in our stomach. Bacteria in beer will also ferment glucose, producing lactic acid by anaerobic respiration. The increase in lactic acid decreases the pH of the beer and gives it its characteristic sour taste.

A student devised an experiment to investigate the concentration of lactic acid in a sample of beer.

Step 1 - Transfer 15 cm3 of beer to a volumetric flask using a beaker.

Step 2 - Make up the volume of the beer to 300 cm3.

Step 3 - Use a pipette to take a portion of 30.0 cm3 and add it to a conical flask.

Step 4 - Give the conical flask an initial swirl and then place on the bench.

Step 5 - Add a few drops of phenolphthalein indicator to the lactic acid in the conical flask.

Step 6 - Titrate samples of 30.0 cm3 of this solution with a 0.0750 mol dm3 solution of sodium hydroxide solution.

Complete Table 1 below.

Table 1

Improvement

Method to achieve improvement

Reduce the overall measurement uncertainty in the titration

 

Improve the chance of obtaining concordant results

 

Improve accuracy of titration by rinsing the conical flask with ...

 

Rinse burette with … for the final rinse

 
4b3 marks

The results of the titration are shown in Table 2.

Table 2

Titration

Rough

1

2

3

Final reading (cm3)

23.20

24.10

48.95

 

Start reading (cm3)

 

0.15

24.10

0.05

Titre (cm3)

23.10

 

23.90

i)
Complete Table 2 by filling in the missing values.

ii)
Calculate the mean titre and give your answers to 2 decimal places.
4c2 marks

The burette used by the student for their titration has an error of ± 0.05 cm3

Suggest the maximum percentage uncertainty in using this piece of equipment using your mean titre calculated in part (b).

4d8 marks

Lactic acidosis occurs when there's too much lactic acid in your body. Causes of lactic acidosis may include chronic alcohol use and can lead to muscle cramps or pain, body weakness and headaches.

Lactic acidosis may occur when the blood levels of lactic acid are 4.0 x 10-3 mol dm-3 or greater.

i)
Calculate the concentration of lactic acid in 300 cm3 of the solution in part (a).
The reaction of lactic acid with sodium hydroxide is as follows:

C6H5COOH + NaOH → C6H5COONa + H2O

ii)
A patient has consumed 5 pints of beer and is worried he may suffer from lactic acidosis as he experiences severe symptoms.
Calculate the amount of lactic acid that the patient has consumed. You may assume that 1 pint is 570 mL.

iii)

Suggest whether the patient has lactic acidosis. Explain your answer using calculation. You may assume that the average adult has about 5500 mL of blood in their body. Note that 1 mL is 1 cm3.

4e6 marks

Another student is required to make up 300 cm3 of an aqueous solution that contains a known mass of lactic acid. The student is provided with a sample bottle containing the lactic acid.

Describe the method, including full apparatus and practical details, that the student should use to prepare this solution.

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5a2 marks

A student investigates the rate of reaction between copper sulfate solution and dilute sodium hydroxide solution.

75 cm3 of copper sulfate solution was poured into a 250 cm3 conical flask using a measuring cylinder.

The conical flask was then placed on a cross drawn on a piece of paper. 15 cm3 of dilute sodium hydroxide was added to the conical flask and the timer was started as shown in Figure 1.

Figure 1

11

The timer was started, and then was stopped when the cross could not be seen anymore. The student then recorded the time.

i)
Write down the equation for the reaction between copper sulfate and dilute sodium hydroxide. 

ii)
Suggest why the cross on the paper disappears.
5b4 marks

The student wants to investigate the effect of temperature on the rate of the reaction described in part (a).

The student carries out the following steps:

Step 1 - Measure out copper sulfate using a beaker and pour it into a conical flask.

Step 2 - Record the initial temperature of the copper sulfate in the conical flask using a thermometer.

Step 3 - Place the flask with the solution onto a cross drawn on a piece of paper.

Step 4 - Heat the sodium hydroxide to a specific temperature.

Step 5 - Start the stopwatch and then add the dilute sodium hydroxide.

Step 6 - Stop the stopwatch when the cross can no longer be seen.

Step 7 - Repeat the experiment at different temperatures.

i)
Identify one key mistake and one improvement to the students method. 

ii)
Suggest two control variables which should remain constant during this experiment.
5c3 marks

From the experiment, the student made the following conclusion:

“The rate of reaction increases with increasing temperature”

Explain whether the student’s conclusion is correct using the collision theory.

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