Data-Based Questions (Paper 1B) (DP IB Chemistry: SL): Exam Questions

A homologous series is a family of compounds with the same functional group and similar chemical properties. The boiling points for the first five straight-chain alkanes are shown in the table and the graph below.

Define the term homologous series.

Describe the relationship between the number of carbon atoms and the boiling point for the alkanes shown in the data.

Using the graph, estimate the boiling point of the next member of the homologous series, hexane (C₆H₁₄).

Explain the trend in boiling points from methane to pentane in terms of the intermolecular forces present.

The boiling point of ethanol (CH₃CH₂OH, M_r = 46.0) is 78 °C.

Explain why this is significantly higher than the boiling point of propane (C₃H₈, M_ᵣ = 44.1), which has a similar molar mass.

Pentane has a branched structural isomer, 2,2-dimethylpropane, which has a boiling point of 10 °C.

Explain why the boiling point of 2,2-dimethylpropane is lower than that of pentane (36 °C).

A student performed a titration to determine the concentration of ethanoic acid (CH₃COOH) in a sample of commercial vinegar. The vinegar was first diluted by a factor of 10. A 25.00 cm³ sample of the diluted vinegar was titrated against a standard solution of 0.100 mol dm^-3 sodium hydroxide (NaOH) using phenolphthalein indicator.

The results of the titration are shown in the table below. The uncertainty for each burette reading is ±0.05 cm³.

Write the balanced chemical equation for the reaction.

State the colour change observed at the end-point of the titration.

i) Calculate the mean titre, in cm³, using the concordant results.

[2]

ii) Calculate the uncertainty of a single titre volume.

[1]

Calculate the concentration, in mol dm^-3, of ethanoic acid in the diluted vinegar.

Calculate the concentration, in mol dm^-3, of ethanoic acid in the original, undiluted vinegar.

The student noticed an air bubble in the tip of the burette after filling it, which was gone by the end of the first accurate titration (Trial 1).

State and explain the effect this error would have on the calculated concentration of ethanoic acid.

The standard enthalpy change of combustion (ΔH_c^Ө) for methane can be determined theoretically using standard enthalpy of formation (ΔH_f^Ө) data. The table below provides relevant values.

Define the term standard enthalpy of formation.

Write the balanced chemical equation for the complete combustion of methane, including state symbols.

Construct a Hess's Law energy cycle using the provided standard enthalpy of formation data to calculate the standard enthalpy change of combustion for methane.

The enthalpy of combustion for methane can also be estimated using average bond enthalpies from section 12 of the data booklet.

Calculate a value for the enthalpy of combustion of methane using this method.

Explain why the value calculated in part (c) is more accurate than the value calculated in part (d).

A sample of H₂O is heated at a constant rate, and its temperature is recorded over time. The process starts with ice at -10 °C and ends with steam at 110 °C. The resulting heating curve is shown below.

i) State the process occurring during section B.

[1]

ii) Identify the section where the substance exists only as a liquid.

[1]

Explain, in terms of the energy of the particles, why the temperature remains constant during section D.

Explain why the length of the plateau in section D is significantly greater than the length of the plateau in section B.

Calculate the heat energy, in kJ, required to raise the temperature of 50.0 g of liquid water from 0 ^oC to 100 ^oC (section C).

The specific heat capacity of liquid water is 4.18 J g^{-1 o}C^-1.

The slope of section A is steeper than the slope of section C.

Suggest what this indicates about the specific heat capacity of ice compared to liquid water.

A student used paper chromatography to separate a mixture of coloured inks. A spot of an unknown mixture, X, and separate spots of three known food dyes, A, B, and C, were placed on a pencil line drawn on a piece of chromatography paper. The paper was then suspended in a beaker containing a non-polar solvent, ensuring the solvent level was below the pencil line. The beaker was covered with a lid.

The resulting chromatogram at the end of the experiment is shown below.

Identify the stationary phase and the mobile phase in this experiment.

Calculate the retardation factor (R_f) for dye B.

Deduce the composition of the unknown mixture X. Justify your answer.

Explain, in terms of adsorption and solubility, why the dyes separate on the chromatogram.

The main component of chromatography paper is cellulose, which is a polar substance.

i) Identify which dye, A, B, or C, has the greatest affinity for the mobile phase.

[1]

ii) Explain why dye C travelled further up the paper than dye A.

[3]

Suggest one reason why the beaker was covered with a lid during the experiment.