Physical Chemistry Practicals (AQA A Level Chemistry)

When a sample of sodium hydroxide, NaOH, is dissolved in 250 cm³ of distilled water. 25.0 cm³ of this solution is titrated against sulfuric acid with a concentration of 2.00 mol dm^-3. Complete neutralisation takes place with 15.0 cm³ of sulfuric acid.

2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O

What is the mass of the original sample of sodium hydroxide dissolved in 250 cm³ of distilled water?

A sample of 2.76 g of ethanol was added to excess acidified aqueous potassium dichromate (VI). The reaction mixture was then boiled under reflux for one hour. The organic product was collected by distillation.

The yield of the product was 75.0%

What is the mass of the product collected?

A student made up a standard solution of sodium hydrogen carbonate using a two decimal place balance and a 250 cm³ volumetric flask.

Which of the following steps would make the final concentration of the solution more accurate?

Zinc reacts with copper sulfate according to the following equation:

Zn(s) + CuSO₄(aq) → Cu(s) + ZnSO₄(aq)

Rates of reaction can be found by measuring how certain properties change during the course of the reaction.

Which of these properties could be used?

25.0 cm³ of hydrochloric acid solutions reacts with 36.2 cm³ of 0.225 mol dm^-3
sodium hydroxide solution. 

What is the concentration of the acid?

Silver nitrate solution reacts with aqueous potassium iodide to form silver iodide and potassium nitrate. Which separation technique could be used to recover the silver iodide?

The enthalpy change of a chemical reaction can be found using the following relationship:

q = mcΔT

In this expression, which of the following is true?

In an acid-base titration, what is the point at which the indicator changes colour known as?

The enthalpy of solution of hydrated copper (II) sulfate can be determined by measuring the temperature changes when a known amount of copper (II) sulfate is added to a fixed volume of water in a calorimeter.

What assumption is not made when calculating the enthalpy change?

The variation of reaction rate with temperature can be investigated using the reaction between sodium thiosulfate solution and hydrochloric acid. The thiosulfate solution is heated to different temperatures and the acid is added to start the reaction. A precipitate of sulfur makes the solution opaque. Placing a cross drawn on paper under the flask enables the ‘end’ of the reaction to be measured using a stopwatch.

Which of the following steps are necessary for each run in the investigation ?

A student used the following method to make a 250 cm³ standard solution of 0.150 mol dm^-3 propanedioic acid.

• Measure out 3.9000 g of propanedioic acid on a 4 decimal place balance.
• Transfer the propanedioic acid to a 250 cm³ beaker.
• Add approximately 50 cm³ of distilled water.
• Stir the mixture to dissolve the propanedioic acid.
• Transfer the solution to a 250 cm³ volumetric flask.
• Add distilled water to the mark.
• Stopper and invert the flask.
• If necessary, add more distilled water to the volumetric flask so that the meniscus is at the mark.

After analysis, the propanedioic acid standard solution was determined to be 0.154 mol dm^-3. 

Which of the following would not account for the concentration of the propanedioic acid standard solution being less than 0.150 mol dm^-3?

A titration experiment was set up to determine the relative formula mass, M_r, anunknown monoprotic acid, HA.

                                                 HA + NaOH → NaA + H₂O

• 2.52 g of HA is used to make a 250 cm³ aqueous solution.
• 25.0 cm³ of 0.136 mol dm^–3 aqueous sodium hydroxide is added to a conical flask.
• The aqueous sodium hydroxide is titrated with the acid solution, HA (aq).

The titration results are as follows.

What is the identity of the unknown monoprotic acid?

Potassium carbonate can form hydrates of the general formula K₂CO₃.xH₂O

A titration experiment was set up to determine the number of moles of water of crystallisation in the hydrated potassium carbonate sample.

A 250 cm³ solution was made by dissolving 3.672 g of a potassium carbonate hydrate in water.

The solution was titrated with 0.18 mol dm^-3 hydrochloric acid.

The titration results are shown in the table.

What is the correct value for x in the formula of this potassium carbonate hydrate, K₂CO₃.xH₂O?

A student carried out an experiment to find the enthalpy change for a reaction between zinc and copper(II) sulfate solution.

• The student used a measuring cylinder to place 70 cm³ of 0.500 mol dm^–3 copper(II) sulfate solution into a polystyrene cup.
• The student recorded the temperature at one-minute intervals for three minutes.
• At the fourth minute the student added 2.00 g of zinc powder and stirred the mixture, but did not record the temperature.
• The student recorded the temperature at one-minute intervals for a further eight minutes.
• After plotting a graph of their results, the student determined that the temperature change, ΔT, for the reaction was 21.70 ^oC.

Assume that the density of the solution is 1 g cm^-3 and the specific heat capacity of the solution is 4.18 J K^-1 g^-1.

What is the enthalpy change for this reaction between zinc and copper(II) sulfate solution?   

When 1.383 g of impure potassium chloride is dissolved in 25.0 cm³ of water the temperature decreases from 22.23 ^oC to 20.02 ^oC. 

The molar enthalpy of dissolution for potassium chloride is 17.30 kJ mol^-1

The specific heat capacity of water is 4.18 J K⁻¹ g⁻¹

What is the percentage purity of potassium chloride used? 

2.65 g of magnesium sulfate is added to 35.0 cm³ of water with an initial temperature of 296.7 K.

The specific heat capacity of water is 4.18 J K⁻¹ g⁻¹.

The enthalpy change of solution for magnesium sulfate is -75.1 kJ mol^-1.

What was the final temperature of the magnesium sulfate solution? 

The reaction between the aqueous copper(II) ion and concentrated hydrochloric acid proceeds according to the following equilibrium. The equilibrium is endothermic in the forward direction.

[Cu(H₂O)₆]²⁺ (aq) + 4Cl^- (aq) ⇌ CuCl₄^2- (aq) + 6H₂O (l) 

The tetrachlorocuprate(II) ion, CuCl₄^2-, produces a yellow colour in solution.

Which of the following statements is not correct?

Two students were asked to use a continuous monitoring method to investigate the effect of changing the concentration of hydrochloric acid on the rate of reaction between hydrochloric acid and calcium carbonate powder.

• Student 1 decided to place the reaction vessel on a balance and measure the mass lost over time. 
• Student 2 decided to connect the reaction vessel to a gas syringe and measure the volume of gas produced over time.

Which is the correct explanation for which student will obtain more accurate results for acid concentrations from 0.1 mol dm^-3 to 2.0 mol dm^-3?

A student investigates the intermolecular forces in cyclohexane, ethanol, propanone and water by allowing the liquids to drain from a burette and observing the resulting deflections of the jet of liquid. The student uses a charged polyethene rod held near the jet.

Which statement about the deflections is correct?

An experiment was set up to determine the identity of an unknown volatile liquid, X, as shown in the diagram.

A hypodermic syringe was used to inject a sample of the unknown volatile liquid X into a gas syringe in an oven, where it vapourised.

Using the information in the table, what is the identity of the unknown volatile liquid, X?

The gas constant R = 8.31 J K^–1 mol^–1