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

The Periodic Table displays the chemical elements, arranged in order of increasing atomic number. It is made up of groups and periods of elements.

State and explain the general trend in first ionisation energy across a period of the Periodic Table.

The general trend in first ionisation energies stated in part (a) is seen across Period 2 of the Periodic Table. However, boron and one other Period 2 element deviate from this trend.

Identify this element and explain why it deviates from the general trend.

State why nitrogen is classed as a p block element and give its full electron configuration.

Identify the Period 3 element that has the lowest melting point.

Explain your answer with reference to bonding and structure.

The conversion of hydrogen and iodine into hydrogen iodide proceeds via a three step reaction mechanism:

1. I₂ (g)   2I (g)                   fast

2. H₂ (g) + I (g)  H₂I (g)      fast

3. H₂I (g) + I (g) → 2HI (g)    slow

Write the rate equation for this reaction and show how the mechanism is consistent with the stoichiometric equation.

An investigation into the rate of reaction between hydrogen and iodine was carried out at 298 K and the data obtained is shown below.

Determine the rate equation for the reaction and justify your answer.

Calculate the rate constant using Expt 2 data, including its units.

Using section 12 of the data booklet, determine whether the forward reaction is favoured by an increase in temperature.

A student investigates the rate of reaction between sodium thiosulfate and hydrochloric acid, which produces a solid sulfur precipitate.

Na₂S₂O₃  +  2HCl  →  2NaCl  +  S  +  SO₂  +  H₂O

The student places a conical flask over a cross drawn on a piece of paper and measures the time taken for the precipitate to obscure the cross.

In this experiment, the rate of reaction is considered to be 1 / time.

Explain why 1 / time can be used as a measure of the initial rate of reaction.

The student investigates the effect of the concentration of sodium thiosulfate on the rate, keeping all other variables constant. The results are shown below.

State and explain the relationship between the concentration of sodium thiosulfate and the rate of reaction.

Sketch a Maxwell-Boltzmann distribution curve.

On the curve, show and explain why a small increase in temperature has a large effect on the rate of this reaction.

Suggest one reason why measuring the reaction time at a very high temperature (e.g., 80 °C) may be less accurate than measuring it at a lower temperature.

The thiosulfate ion, S₂O₃^2-, contains sulfur in one oxidation state, which is converted into two different oxidation states in the products.

Deduce the oxidation state of sulfur in the thiosulfate ion.

A branched ester is synthesized via the three-step reaction pathway shown below.

Deduce the IUPAC name and draw the displayed structural formula of compounds A and B.

For Step 1 and Step 2, state the class of reaction and a suitable reagent.

Draw the skeletal formula of the final ester product and state its IUPAC name.

The esterification reaction (step 3) is reversible.

State the two reagents and conditions needed to hydrolyse the ester and reform compounds A and B.

Compound B can exist as two enantiomers.

Draw the 3D representation of both enantiomers of compound B, indicating the chiral centre with an asterisk (*).

This question is about free radical substitution. 

1,2-dibromoethane reacts with bromine in UV light to produce a mixture of further substituted haloalkanes. 

i) Write an equation for the initiation step. 

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ii) Explain why this is an example of homolytic fission. 

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Write two equations showing the propagation of this chain reaction to produce 1,1,2-tribromoethane. 

Traces of 1,2,3,4-tetrabromobutane are found in the reaction mixture. 

i) Write an equation to show how this product is formed. 

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ii) Write a balanced symbol equation to show the overall reaction between 1,1,2-tribromoethane with bromine in UV light to form hexabromoethane. 

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Propanoic acid, CH₃CH₂COOH, is a weak monoprotic acid with a pK_a of 4.87 at 298 K.

Calculate the pH of a 0.500 mol dm^-3 solution of propanoic acid.

A 40.0 cm³ sample of 0.500 mol dm^-3 propanoic acid is titrated with 0.250 mol dm^-3 sodium hydroxide solution.

i) Calculate the volume of sodium hydroxide solution required to reach the equivalence point.

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ii) Determine the pH of the solution at the half-equivalence point. Justify your answer.

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In a separate experiment, the titration is performed in an insulated calorimeter. The total volume of the mixture at the equivalence point is 120.0 cm³.

The temperature is observed to increase by 2.15 °C during the neutralisation.

i) Using your answer from (b)(i), determine the standard enthalpy of neutralisation, in kJ mol⁻¹, for the reaction between propanoic acid and sodium hydroxide.

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ii) State two assumptions made in this calculation.

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The standard enthalpy of neutralisation for the reaction between a strong acid and a strong base is approximately -57 kJ mol^-1.

Explain why the value calculated for propanoic acid is significantly less exothermic.

The structure of propanoic acid is CH₃CH₂COOH. Predict the key features of its high-resolution ¹H NMR spectrum by completing the table below.

Propene (CH₃CH=CH₂) is a valuable chemical feedstock used in the production of polymers and other organic chemicals. Its properties and reactions are dictated by its structure.

i) State the number of sigma (σ) and pi (π) bonds in one molecule of propene.

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ii) State the hybridisation of the carbon atoms labelled 1 and 3 in the structure above and predict the H-C1-H bond angle.

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Propene can be polymerised to form poly(propene).

i) State the type of polymerisation.

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ii) Draw the structure of the repeating unit of poly(propene).

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Propene reacts with hydrogen bromide (HBr) via an electrophilic addition mechanism.

i) Draw the structure of the major organic product formed in this reaction.

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ii) Explain why this is the major product by drawing the structures of the two possible carbocation intermediates and comparing their stability.

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Propene can be hydrogenated to form propane in the presence of a nickel catalyst.

CH₃CH=CH₂ (g) + H₂ (g) → CH₃CH₂CH₃ (g)

Using the average bond enthalpies from section 12 of the data booklet, calculate the standard enthalpy change (ΔH°) for this reaction.

Suggest how infrared (IR) spectroscopy could be used to monitor the progress of the hydrogenation reaction in part (d) and confirm that all the propene has been converted to propane.

Use section 20 of the data booklet in your answer.

Limonene (C₁₀H₁₆) is a natural cyclic alkene responsible for the characteristic smell of oranges and lemons. It is used in cleaning products, as a fragrance, and as a starting material for chemical synthesis.

i) The structure of limonene contains a chiral centre. Identify the chiral carbon on the structure by marking it with an asterisk (*).

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ii) State the empirical formula of limonene.

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iii) Limonene has several structural isomers that are also cyclic alkenes. Draw the skeletal structure of a structural isomer of limonene that has a five-membered ring.

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The standard enthalpy of combustion (ΔH^θ_c) of liquid limonene is -6110 kJ mol⁻¹.

i) Write a balanced chemical equation for the complete combustion of limonene.

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ii) Calculate the mass of limonene, in grams, that must be burned to release 1000 kJ of heat energy.

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Limonene has two C=C double bonds. When one mole of limonene reacts with exactly one mole of bromine (Br₂) in an inert solvent, the bromine preferentially adds across the double bond that is outside the ring.

i) Draw the skeletal structure of the major organic product of this reaction.

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ii) Explain, in terms of bond stability and steric hindrance, why this double bond is more reactive than the one within the six-membered ring.

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When limonene is treated with excess hydrogen chloride (HCl), addition occurs at both double bonds. According to Markovnikov's rule, a single major final product is formed.

i) Draw the skeletal structure of the final major product.

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ii) The first addition of HCl is faster than the second. Suggest a reason for this difference in reaction rates.

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The complete hydrogenation of one mole of limonene gas consumes two moles of hydrogen gas to form a saturated cyclic alkane called menthane.

C₁₀H₁₆ (g) + 2H₂ (g) → C₁₀H₂₀ (g)

i) Predict the sign of the standard entropy change (ΔS°) for this reaction and justify your answer.

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ii) Given that the reaction is highly exothermic (ΔH^θ is very negative), explain how temperature would affect the spontaneity of this reaction.

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The thermal decomposition of Group 2 metal carbonates is a key reaction demonstrating periodic trends. The general equation for the reaction is:

MCO₃ (s) → MO (s) + CO₂ (g)

Explain the trend in ionic radius for the M²⁺ ions down Group 2, from Mg²⁺ to Ba²⁺.

The standard enthalpy of decomposition, ΔH^θ , becomes progressively more endothermic down Group 2.

Explain this trend by considering the relative lattice enthalpies of the metal carbonates (MCO₃) and the metal oxides (MO).

For the decomposition of magnesium carbonate, MgCO₃, at 298 K:

ΔH^θ = +100.6 kJ mol⁻¹
ΔS^θ = +175.0 J K⁻¹ mol⁻¹

i) Calculate the standard Gibbs free energy change, ΔG^θ, for this reaction at 298 K.

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ii) Deduce, giving a reason, whether the decomposition of magnesium carbonate is spontaneous at 298 K.

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i) Calculate the minimum temperature, in K, at which the decomposition of magnesium carbonate becomes spontaneous.

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ii) State one assumption you have made.

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Using your understanding of periodic trends and thermodynamic principles from parts (a) to (d), predict and explain how the decomposition temperature of barium carbonate (BaCO₃) would compare to that of magnesium carbonate.