Synoptic Exam Questions (Paper 2) (DP IB Chemistry: SL): Exam Questions

A student performed a titration to identify an unknown dicarboxylic acid, X, which only contains carbon, hydrogen and oxygen. 

A 1.513 g sample of X was dissolved and made up to a 250.0 cm³ standard solution. This solution was placed in a burette. A 25.00 cm³ aliquot of 0.112 mol dm^-3 NaOH(aq) was titrated, and the titration results were recorded.

The equation for the reaction is:

X (aq) + 2NaOH (aq) → Na₂X (aq) + 2H₂O (l)

i) Calculate the mean titre. 

[1]

ii) Determine the amount, in moles, of X present in the original 250.0 cm³ sample.

   [3]

i) Determine the molar mass of X.

[1]

ii) Suggest a possible structure for X.

[2]

A student performs a series of experiments to investigate the kinetics of the acid-catalysed iodination of propanone. The overall reaction is:

CH₃COCH₃ (aq) + I₂ (aq) → CH₃COCH₂I (aq) + H⁺ (aq) + I^- (aq)

The reaction can be monitored by observing the disappearance of the brown colour of the aqueous iodine. Suggest a suitable piece of apparatus for quantitatively measuring this change in colour.

Sketch a Maxwell-Boltzmann distribution curve. On your sketch, label the axes and show how the addition of the H⁺ catalyst affects the activation energy of the reaction.

Draw the skeletal formula for the organic product, 1-iodopropan-2-one.

In this reaction, iodine acts as an oxidising agent.

State the change in oxidation state of an iodine atom when I₂ is converted to the iodide ion, I^-.

An alternative method for monitoring the reaction is to withdraw samples at regular intervals, quench the reaction, and titrate the remaining iodine with a standard solution of sodium thiosulfate, Na₂S₂O₃ (aq). The titration reaction is:

I₂ (aq) + 2S₂O₃^2- (aq) → 2I^- (aq) + S₄O₆^2- (aq)

If a sample was found to contain 1.25 × 10^-4 moles of iodine, calculate the mass, in mg, of the sulfur precipitate (S) that would form.

Marble chips are added separately to solutions of the same concentration of ethanoic acid and hydrochloric acid. State one similarity and one difference you would expect to observe in the reactions.

Write an equation for the reaction between marble chips and ethanoic acid.

Determine the volume, in cm³, of 2.25 mol dm^-3 ethanoic acid needed to completely react with 1.50 g of marble chips. 

Determine the volume of CO₂, in cm³, produced at 273 K and 101 kPa in part c).

The reaction between iron(II) ions and permanganate ions in acidic solution is used to analyze the iron content in supplements.

      5Fe²⁺ (aq) + MnO₄^- (aq) +8H⁺ (aq) → 5Fe³⁺ (aq) + Mn²⁺ (aq) + 4H₂O (l) 

Deduce the change in oxidation state for:

i) Iron

[1]

ii) Manganese

[1]

Identify, with a reason, the oxidising agent in this reaction.

The amount of iron in some dietary iron supplements was analyzed by redox titration. Four tablets were crushed and dissolved in 50.0 cm³ of 2.00 mol dm^-3 sulfuric acid. The solution was then transferred to a 250 cm³ volumetric flask and made up to 250 cm³ with distilled water. 

A 25.0 cm³ sample of the iron tablets solution was titrated against 0.00500 mol dm^-3 potassium manganate(VII) and 25.8 cm³ was needed for complete reaction. 

Determine the amount of iron, in mol, in one tablet.

Using the standard enthalpy of combustion data below (from section 14 of the data booklet), calculate the standard enthalpy change for the hydrogenation of ethyne to ethene.

C₂H₂ (g) + H₂ (g) → C₂H₄ (g)

A student has two separate 1.00 dm³ samples of ethene and ethyne gas at standard temperature and pressure (STP).

Calculate the maximum volume of 0.0500 mol dm^-3 aqueous bromine (Br₂ (aq)) that can be completely decolorised by each gas sample.

Explain why the hydrogen atoms in ethyne are weakly acidic, whereas the hydrogen atoms in ethene are not considered acidic. Refer to the hybridisation of the carbon atoms in your answer.

A student performs a calorimetry experiment to determine the enthalpy of reaction when lithium metal reacts with water. They add a small piece of lithium to water in a polystyrene cup and record the temperature change.

i) Apart from the change in temperature, state two observations the student would make during this reaction.

[2]

ii) Write a balanced chemical equation for the reaction, including state symbols.

[1]

i) Using section 2 of the data booklet, calculate the heat energy (Q) absorbed by the water, in kJ.

[2]

ii) Determine the limiting reactant in this experiment.

[2]

iii) Calculate the enthalpy change (ΔH) for the reaction, in kJ mol⁻¹.

[1]

The accepted literature value for this reaction is -222 kJ mol⁻¹.

Suggest a reason why the student's experimental value is different.

Predict, with a reason, how the initial rate of reaction would differ if an equimolar amount of potassium were used instead of lithium.

Calculate the volume of gas produced, in dm³, measured at standard temperature and pressure. Use section 2 of the data booklet.