Chemistry HL Paper 2, specimen 2025

Determine the empirical formula of HA from the percentage composition.

A solution is prepared by dissolving 1.29 g of HA in water and making the volume up to $20.00\ \mathrm{cm^3}$. When the whole of this solution is titrated with $0.600\ \mathrm{mol\,dm^{-3}}$ sodium hydroxide, NaOH(aq), exactly $24.90\ \mathrm{cm^3}$ of the…

State the molecular formula of HA, using your answers to (a) and (b).

HA reacts with aqueous sodium carbonate according to the equation: $\ce{2HA(aq) + Na2CO3(aq) -> 2NaA(aq) + CO2(g) + H2O(l)}$ Identify the functional group in HA that is responsible for this reaction.

The IR spectrum of HA is shown. Two absorption bands are labelled: Y is a very broad band centred near $3000\ \mathrm{cm^{-1}}$ and Z is a band of medium intensity near $1650\ \mathrm{cm^{-1}}$. (i) Using section 20 of the data booklet, identify the functional…

α-particles are the nuclei of helium-4 atoms. In an experiment based on the work of Geiger and Marsden, a beam of α-particles is directed at a very thin platinum foil and the angle of deflection, θ, of each particle is recorded by a detector that can be moved…

The presence of hydrogen in stars is deduced from lines in their spectra. (i) Outline what the emission spectrum of hydrogen looks like. Emission spectra of species that contain a single electron can be explained by a model in which the electron is held by the…

Outline why scientists have replaced earlier models of the atom with new ones.

Below is a sodium-ion cell as it discharges, supplying a current to an external circuit. The anode is sodium held in a lattice of hard carbon and the cathode is iron(III) phosphate, $\ce{FePO4}$, which is converted to $\ce{NaFePO4}$ as the cell discharges.…

When the cell discharges, a spontaneous redox reaction generates a potential difference between the electrodes and the temperature of the cell rises. (i) Deduce the signs of $\Delta H_\mathrm{discharge}$, $E_\mathrm{cell}$ and $\Delta G_\mathrm{discharge}$.…

A computer simulation models what happens when small pieces of lithium and of sodium are dropped into water. For each metal five pieces of increasing mass are used, the same set of masses for both metals, and the simulation records how long each piece takes to…

A small volume of $0.050\ \mathrm{mol\,dm^{-3}}$ hydrobromic acid is placed in a beaker fitted with a pH probe. Distilled water is then run into the beaker at a constant rate and the pH is logged continuously; the temperature is held at 298 K. (i) Sketch, on…

Chloride ions can act as ligands towards transition metal ions. Three compounds of chromium that differ in the number of chloride ions bonded directly to the chromium ion have the formulas and colours shown. Compound Colour $\ce{[Cr(H2O)6]Cl3}$ violet…

Complete combustion turns pentadecane entirely into carbon dioxide and water. Write the corresponding balanced equation.

The enthalpy of combustion of $\ce{C15H32}$ is $-10\,040\ \mathrm{kJ\,mol^{-1}}$. (i) Calculate the maximum amount of energy that the complete combustion of 1.75 g of pentadecane can release. (ii) The energy from burning the 1.75 g sample is used to heat…

Pentadecane produced by cyanobacteria can be used as a biofuel. Explain why burning this biofuel adds less to the long-term buildup of atmospheric carbon dioxide than burning the same mass of pentadecane refined from crude oil.

Pentadecane can be cracked into smaller molecules. Consider the reaction: $\ce{C15H32(g) -> 3C4H8(g) + C3H8(g)}$ where $\ce{C4H8}$ is but-1-ene. (i) Use the bond enthalpies in section 12 of the data booklet to determine $\Delta H^\ominus$ for this reaction.…

But-1-ene is converted into butan-2-ol in a single reaction. State the corresponding equation.

Butan-2-ol reacts with octadecanoic (stearic) acid to form an ester that is used as a lubricant. $\ce{C17H35COOH(l) + CH3CH(OH)CH2CH3(l) <=> C17H35COOCH(CH3)CH2CH3(l) + X(l)}$ (i) Identify the by-product X(l) and state the type of reaction taking place. (ii)…

The equilibrium constant, $K_\mathrm{c}$, for the reaction in (f) is $6.4 \times 10^{-5}$ at 80 °C. (i) $1.00\ \mathrm{dm^3}$ of a mixture that is initially $0.20\ \mathrm{mol\,dm^{-3}}$ in octadecanoic acid and $0.20\ \mathrm{mol\,dm^{-3}}$ in butan-2-ol is…

(i) Iodine molecules, $\ce{I2}$, undergo homolytic fission when they absorb light. Write an equation for this process, using curly arrows to show the movement of the electrons. (ii) In the presence of a suitable reagent the I–I bond can instead break…

The boiling points of the five simplest straight-chain primary amines, $\ce{CH3NH2}$ to $\ce{CH3(CH2)4NH2}$, and of the five simplest 1-fluoroalkanes, $\ce{CH3F}$ to $\ce{CH3(CH2)4F}$, are plotted below against the number of carbon atoms in the molecule. An…

(i) Draw the structural formula of 2-chloropentane and that of the structural isomer in which the chlorine atom is attached to a tertiary carbon atom. (ii) Only one of the two isomers drawn in (c)(i) is chiral. Draw stereochemical formulas showing its two…