Feb/March 2024

Which species has the same number of neutrons as $^{14}_{6}\text{C}$ and the same number of electrons as $^{23}_{11}\text{Na}^+$?

Atomic structure

Which reaction corresponds to the standard enthalpy change of formation of propane?

Chemical energetics

The equation below represents one reaction in a rechargeable lead/acid battery. $\text{Pb}(s) + \text{PbO}_2(s) + 4\text{H}^+(aq) + 2\text{SO}_4^{2-}(aq) \rightarrow 2\text{PbSO}_4(s) + 2\text{H}_2\text{O}(l)$. Which statement concerning this reaction is correct?

Electrochemistry

$\text{KMnO}_4$ acts as an oxidising agent. Its reaction with $\text{Fe}^{2+}$ is represented by the ionic equation below. $\ldots X\ldots \text{MnO}_4^- + \ldots \text{Fe}^{2+} + \ldots \text{H}^+ \rightarrow \ldots \text{Mn}^{2+} + \ldots Y\ldots \text{Fe}^{3+} + \ldots \text{H}_2\text{O}$ When the equation is balanced, what are $X$ and $Y$?

Electrochemistry

Nitrogen and hydrogen are combined in a reaction vessel. Equilibrium is then established, producing a gaseous mixture of nitrogen, hydrogen and ammonia. $\text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3$ At equilibrium, the gas mixture has a total pressure of $300\,\text{atm}$. The amounts present are shown below. Nitrogen: $180$ mol Hydrogen: $590$ mol Ammonia: $160$ mol Calculate the equilibrium constant, $K_p$, for the forward reaction.

Equilibria

A gaseous mixture of hydrogen gas and iodine gas is contained in a reaction vessel with volume $V$ at temperature $T$. The reaction $\text{H}_2 + \text{I}_2 \rightleftharpoons 2\text{HI}$ is then allowed to reach equilibrium. Every substance stays in the gaseous state. Argon gas is next introduced into the reaction vessel. The temperature inside the vessel is kept at $T$. What happens to the rate of the forward reaction and the partial pressure of HI at equilibrium?

Equilibria

Two experiments are performed to investigate the reaction between zinc and sulfuric acid. experiment 1: Small pieces of zinc are placed into an excess of dilute sulfuric acid. experiment 2: The reaction is carried out at a lower temperature, together with one further alteration. Both experiments give the same total volume of gas and finish in the same time. What is the other change made in experiment 2?

Reaction kinetics

The relative size of property $X$ for five elements is shown below. $P$, $Q$, $R$, $S$ and $T$ are all in Period 3 and have successive atomic numbers. The letters do not represent the real chemical symbols of the elements. Which row gives the correct answer for property $X$ and element $R$?

The Periodic Table: chemical periodicity

Element $X$ belongs to Period 3. Element $X$ reacts with oxygen to form a solid, $Y$. If solid $Y$ is placed in water, it gives a solution with a pH of less than $7$. Which element is $X$?

The Periodic Table: chemical periodicity

This question is about isolated gaseous species. The species $\text{F}^-$, Ne and $\text{Na}^+$ are isoelectronic. This indicates that they contain the same number of electrons. In what sequence do their radii increase?

The Periodic Table: chemical periodicity

Separate samples of magnesium and calcium are placed into an excess of dilute sulfuric acid. The results are shown in the table. Magnesium: reacts vigorously, bubbles of gas are given off, magnesium dissolves completely. Calcium: reacts vigorously at first, bubbles of gas are given off, the reaction soon stops and most of the calcium remains unreacted. Which statement accounts for the difference in these observations?

Group 2

Which process has the greatest enthalpy change per mole?

Chemical energetics

Dolomite is a double carbonate, $\text{CaMg(CO}_3)_2$, and may be used in place of calcium carbonate for treating acidic soils. All three statements are about the agricultural use of these carbonates. Which statements are correct?

Group 2

This question concerns two salts, NaI and NaCl. Each of the two solid salts is added separately to warm concentrated $\text{H}_2\text{SO}_4$, and the observations are recorded. Aqueous solutions of the two salts are each mixed separately with $\text{AgNO}_3$(aq), after which concentrated $\text{NH}_3$(aq) is added, and the observations are recorded. Which row is correct?

Group 17

The diagram illustrates the procedure of placing calcium nitrate and strontium nitrate into separate boiling tubes and then heating them. The same conditions are applied. While the reactions continue, the water containing universal indicator changes colour. Which row gives the colour change and identifies the nitrate that produces the fastest colour change?

Reaction kinetics

Three reaction equations involving chlorine or chlorine compounds are given below. 1. $2\text{KClO}_3 \rightarrow 2\text{KCl} + 3\text{O}_2$ 2. $4\text{KClO}_3 \rightarrow 3\text{KClO}_4 + \text{KCl}$ 3. $6\text{KOH} + 3\text{Cl}_2 \rightarrow 3\text{H}_2\text{O} + 5\text{KCl} + \text{KClO}_3$ Which statement is correct for these equations?

Electrochemistry

Nitrogen monoxide, NO, is a primary pollutant formed by petrol engines and present in their exhaust gases. Which reaction takes place in a catalytic converter and reduces the amount of nitrogen monoxide released?

Nitrogen and sulfur

The diagram illustrates the structure of the naturally occurring molecule cholesterol. Student X said that all 17 carbon atoms in the 4 rings are in one plane. Student Y said that this molecule shows cis/trans isomerism at the C=C double bond. Which students are correct?

Chemical bonding

The drug cortisone has the formula shown. Besides the chiral centres indicated with an asterisk (*), how many additional chiral centres are there in the cortisone molecule?

Chemical bonding

When But-2-ene is treated with cold, dilute, acidified $\text{KMnO}_4$, product X is formed. When But-2-ene is treated with hot, concentrated, acidified $\text{KMnO}_4$, product Y is formed. Which statement about product X and product Y is correct?

Hydrocarbons

A series of reactions occurs, and the main product is compound Z. propanoic acid $\xrightarrow{\text{LiAlH}_4}$ compound X $\xrightarrow{\text{concentrated } \text{H}_2\text{SO}_4}$ compound Y $\xrightarrow{\text{pass vapour with steam over } \text{H}_3\text{PO}_4}$ compound Z What is compound Z?

Organic synthesis

Which of the following statements is correct?

Atoms, molecules and stoichiometry

Which sodium compound has a sodium mass percentage of $74.2\%$?

Atoms, molecules and stoichiometry

During the hydrolysis of bromoethane with aqueous NaOH, what are the identities of the attacking group and the leaving group?

Halogen compounds

X is an organic compound made up of carbon, hydrogen and oxygen only. The table below records the observations from three chemical tests on X. Reagent added and observation: - Na(s): effervescence - Na$_2$CO$_3$(s): effervescence - hot H$^+$/Cr$_2$O$_7^{2-}$(aq): remains orange What could be a possible structure of X?

Carboxylic acids and derivatives

How many moles of oxygen gas are required for the complete combustion of $1\ \text{mol}$ of $(\text{CH}_3)_3\text{COH}$?

Atoms, molecules and stoichiometry

For which pair will each compound produce a different observable outcome with alkaline I$_2$(aq)?

Carbonyl compounds

Which reagent produces a positive test for propanone?

Carbonyl compounds

Esters may be hydrolysed using an aqueous alkali or an aqueous acid, giving two products. The table compares these two approaches. Which row is correct?

Equilibria

Only structural isomerism should be taken into account when answering this question. How many compounds having molecular formula $\text{C}_5\text{H}_{11}\text{Br}$ are primary halogenoalkanes?

Halogen compounds

Compound Z is made by the reaction sequence shown below. $\text{CH}_3\text{CH}_2\text{Br}$ $\xrightarrow[\text{in ethanol}]{\text{warm with KCN}}$ compound X $\xrightarrow[\text{dilute HCl}]{\text{reflux}}$ compound Z What is the molecular formula of compound Z?

Carboxylic acids and derivatives

Hydroxyethanal, $\text{HOCH}_2\text{CHO}$, is heated under reflux in excess acidified $\text{K}_2\text{Cr}_2\text{O}_7$ until oxidation can no longer occur. Which skeletal formula represents the organic product?

Electrochemistry

The formula shows the repeat unit of an addition polymer, $-\text{CH}(\text{CH}_3)\text{CH}(\text{CH}_2\text{CH}_3)-$. What is the correct name of the monomer from which this polymer is produced?

Chemical bonding

What is the largest volume of sulfur dioxide gas, measured under room conditions, that can be formed by burning $100\,\text{dm}^3$ of diesel fuel that contains $0.8346\,\text{g}$ of sulfur?

Atoms, molecules and stoichiometry

An infrared spectrum for a compound is displayed. Which functional group might be present in the compound?

Analytical techniques

Which row gives the correct count of covalent bonds in a molecule of methylpropene?

Chemical bonding

At room temperature, aluminium chloride is present as $\text{Al}_2\text{Cl}_6$ molecules. On heating to a high temperature, $\text{AlCl}_3$ molecules form. What are the arrangements of the bonding pairs of electrons around the aluminium atom in these two forms of aluminium chloride?

Chemical bonding

The table presents the physical properties of four substances. Which substance has a giant covalent structure?

Chemical bonding

Under room temperature and pressure, $\text{H}_2\text{O}$ is a liquid whereas $\text{H}_2\text{S}$ is a gas. What causes this difference in state?

States of matter

For the reaction below, the enthalpy change is given as $\Delta H_r^\circ$. $2\text{C}_2\text{H}_6(g) + 3\text{O}_2(g) \rightarrow 2\text{CH}_4(g) + 2\text{CO}_2(g) + 2\text{H}_2\text{O}(l)$. Which expression could be used to determine $\Delta H_r^$?

Chemical energetics

Bismuth belongs to Group 15 of the Periodic Table.

Nitrogen and sulfur

Chlorine, Cl$_2$, takes part in reactions with many elements and compounds, producing chlorides. Table 2.1 gives details of some chlorides of Period 3 elements.

Group 17

Nitrogen, N$_2$, is usually a molecule that is not very reactive, although it does react in some conditions.

Nitrogen and sulfur

Compound S is a food flavouring. One possible route for the synthesis of S is shown in Fig. 4.1.

An introduction to AS Level organic chemistry

Potassium iodide, KI, serves as a reagent in both inorganic chemistry and organic chemistry.

Chemical energetics

Water is an amphoteric substance and is also an effective solvent for polar and ionic compounds.

Equilibria

Iron is a transition metal placed in Group 8 of the Periodic Table.

Chemistry of transition elements

Ruthenium and osmium are transition metals positioned beneath iron in Group 8 of the Periodic Table.

Chemistry of transition elements

Compound $Q$ may be synthesised from chlorobenzene in seven steps by the route shown in Fig. 5.1.

Organic synthesis

Amino acids are molecules containing the functional groups $\text{-NH}_2$ and $\text{-COOH}$. Glycine, $\text{H}_2\text{NCH}_2\text{COOH}$, is the simplest amino acid that is stable.

Nitrogen compounds