Chemistry SL Paper 1A, May 2025, TZ1

A beam containing protons, neutrons and electrons is passed between two charged metal plates. The three paths observed are labelled P, Q and R. Which row correctly identifies the particle following each path? A. P: electron, Q: proton, R: neutron B. P: proton,…

The letters below stand for four species, not for element symbols. Which pair of species has an identical number of outer-shell electrons? $\ce{^{31}_{15}J^{2-}}$, $\ce{^{40}_{18}L^{+}}$, $\ce{^{39}_{19}M^{+}}$, $\ce{^{32}_{16}Q^{2+}}$ A. J and M B. L and Q C.…

Which diagram shows the electron configuration of an oxygen atom in its ground state? A. Diagram A B. Diagram B C. Diagram C D. Diagram D

Which row shows the gas and the conditions under which its behaviour is closest to that of an ideal gas? A. Hydrogen fluoride, $\ce{HF}$, at high pressure and low temperature B. Methane, $\ce{CH4}$, at high pressure and low temperature C. Hydrogen fluoride,…

Three orbital shapes, labelled I, II and III, are drawn below. Which row correctly identifies the shapes of a 2s orbital and a 2p orbital? A. 2s: II, 2p: I B. 2s: I, 2p: III C. 2s: I, 2p: II D. 2s: III, 2p: II

A fixed amount of an ideal gas is kept at constant temperature while the volume of its container is decreased by 60 %. How does the pressure of the gas change? $pV = nRT$ A. Pressure decreases by 60 % B. Pressure increases by 60 % C. Pressure increases by 150…

Which row shows the correct formula of aluminium sulfide and the electron configuration of each species in it? A. $\ce{Al3S2}$; Al species [Ne]; S species [Ar] B. $\ce{Al2S3}$; Al species [Ne] $3s^2\,3p^1$; S species [Ne] $3s^2\,3p^4$ C. $\ce{Al2S3}$; Al…

Four allotropes of carbon, labelled W, X, Y and Z, are described in the table. Allotrope Description W a single flat sheet of hexagonal rings, one atom thick, in which each carbon atom is bonded to three others X a closed cage of 60 atoms made of pentagonal…

For which of these molecules is the octet rule satisfied by every atom? I. $\ce{SiCl4}$ II. $\ce{NCl3}$ III. $\ce{BCl3}$ A. I and II only B. I and III only C. II and III only D. I, II and III

Which of these compounds has the weakest ionic bond? A. $\ce{SrO}$ B. $\ce{BaO}$ C. $\ce{SrS}$ D. $\ce{BaS}$

Which row lists these molecules in order of increasing bond angle? A. $\ce{NF3}$, $\ce{SiH4}$, $\ce{HCHO}$, $\ce{C2H2}$ B. $\ce{SiH4}$, $\ce{NF3}$, $\ce{HCHO}$, $\ce{C2H2}$ C. $\ce{NF3}$, $\ce{HCHO}$, $\ce{SiH4}$, $\ce{C2H2}$ D. $\ce{C2H2}$, $\ce{HCHO}$,…

A mixture of biphenyl, $\ce{C12H10}$, and 4-phenylphenol, $\ce{C12H10O}$, was separated by thin-layer chromatography on a polar silica plate, using the non-polar solvent cyclohexane as the mobile phase. What are the position and the retardation factor…

Simple bonding theory expects every atom in a covalent molecule to end up with eight valence electrons. Two stable gas-phase molecules, $\ce{BF3(g)}$ and $\ce{BeF2(g)}$, do not fit this picture. Which adaptation of the bonding model was needed to explain…

Phosphorus occurs as the atom and as several ions. In which row are the species arranged from the smallest radius to the largest? A. $\ce{P^{3-}}$, $\ce{P}$, $\ce{P^{3+}}$, $\ce{P^{5+}}$ B. $\ce{P^{5+}}$, $\ce{P^{3+}}$, $\ce{P}$, $\ce{P^{3-}}$ C. $\ce{P}$,…

Which statement explains why the atomic radius decreases across period 3 from magnesium, Mg, to sulfur, S? A. The number of occupied main energy levels increases B. The shielding effect of the inner electrons decreases C. The number of protons in the nucleus…

Which pair of elements would react together most vigorously? A. $\ce{Na(s)}$ and $\ce{I2(s)}$ B. $\ce{Cs(s)}$ and $\ce{I2(s)}$ C. $\ce{Na(s)}$ and $\ce{F2(g)}$ D. $\ce{Cs(s)}$ and $\ce{F2(g)}$

Sulfur has different oxidation states in hydrogen sulfide, $\ce{H2S}$, and in sulfurous acid, $\ce{H2SO3}$. Which pair of values is correct? A. $\ce{H2S}$: +2; $\ce{H2SO3}$: +4 B. $\ce{H2S}$: −2; $\ce{H2SO3}$: +6 C. $\ce{H2S}$: −2; $\ce{H2SO3}$: +4 D.…

A chemical reaction occurs in a mixture that starts at the same temperature as its surroundings. Immediately after the reaction, the mixture is warmer than before. Which row correctly describes the energy changes in the system and in the surroundings as the…

A student stirred 0.030 mol of solid sodium hydrogencarbonate into 40 $\mathrm{cm^3}$ of a 1.0 $\mathrm{mol\,dm^{-3}}$ solution of ethanedioic acid. $\ce{H2C2O4(aq) + 2NaHCO3(s) -> Na2C2O4(aq) + 2CO2(g) + 2H2O(l)}$ The temperature of the solution fell from…

One route to 2-bromopropane is the substitution of propane by bromine in ultraviolet light. $\ce{C3H8(g) + Br2(g) -> C3H7Br(g) + HBr(g)}$ ($\ce{C3H8}$ = 44.11 $\mathrm{g\,mol^{-1}}$, $\ce{Br2}$ = 159.80 $\mathrm{g\,mol^{-1}}$, $\ce{C3H7Br}$ = 123.00…

30 $\mathrm{cm^3}$ of butane was completely burned in 250 $\mathrm{cm^3}$ of oxygen according to the following equation. $\ce{2C4H10(g) + 13O2(g) -> 8CO2(g) + 10H2O(l)}$ What volume of oxygen remains unreacted, measured at the original conditions? A. 55…

The Maxwell–Boltzmann distribution below was obtained for a sample of gas at temperature $T_1$. The activation energy of a reaction is marked as $E_\mathrm{a}$. Which graph shows the distribution for the same sample at a higher temperature, $T_2$, together…

In a kinetics experiment, excess dilute hydrochloric acid was added to a fixed mass of marble chips (calcium carbonate), and the volume of carbon dioxide gas produced was measured over time. What is the average rate of gas production for the first 20 seconds?…

A sealed, rigid container holds the following gas-phase reaction at equilibrium. $\ce{N2(g) + O2(g) <=> 2NO(g)}$ $\Delta H^\ominus = +180\ \mathrm{kJ\,mol^{-1}}$ Which pair of changes would move the equilibrium position furthest towards the products? A.…

Which two species can act both as Brønsted–Lowry acids and as Brønsted–Lowry bases? A. $\ce{H2CO3}$ and $\ce{CO3^{2-}}$ B. $\ce{HCO3-}$ and $\ce{SO3^{2-}}$ C. $\ce{HCO3-}$ and $\ce{HSO3-}$ D. $\ce{H2SO3}$ and $\ce{HSO3-}$

The pH of a solution is measured as 4.0. Which value, in $\mathrm{mol\,dm^{-3}}$, is the hydrogen-ion concentration, $[\ce{H+}]$, of this solution? A. $4.0 \times 10^{-4}$ B. $1.0 \times 10^{-4}$ C. $1.0 \times 10^{4}$ D. $4.0 \times 10^{4}$

Part of the reactivity series of metals is shown, from the most reactive to the least reactive. Mg, Al, Mn, Zn, Fe, Ni, Sn, Pb, Cu, Ag Which reaction is spontaneous? A. $\ce{Fe^{2+}(aq) + Ni(s) -> Ni^{2+}(aq) + Fe(s)}$ B.…

Which alcohol and which conditions would give the highest yield of 3-methylbutanoic acid on oxidation with acidified potassium dichromate(VI)? A. 3-methylbutan-2-ol, reflux B. 3-methylbutan-1-ol, distillation C. 3-methylbutan-1-ol, reflux D.…

Which diagram correctly shows the heterolytic fission of the carbon-bromine bond in bromomethane? A. Diagram A B. Diagram B C. Diagram C D. Diagram D

A direct formic acid fuel cell generates electricity by oxidizing formic acid, $\ce{HCOOH}$, with oxygen at the two electrodes, shown below as separate half-equations. Anode: $\ce{HCOOH(aq) -> CO2(g) + 2H+(aq) + 2e-}$ Cathode:…