Chemistry HL Paper 1A, November 2025, TZ1

Which methods for separating the components of the given mixtures are correct? Mixture Method I. Two miscible liquids with boiling points of 56 °C and 118 °C Distillation II. The coloured pigments extracted from a leaf Paper chromatography III. A solid…

Bromine is a diatomic element made up of two isotopes, $\ce{^{79}Br}$ and $\ce{^{81}Br}$, in an approximately 1 : 1 ratio. Which graph shows the full mass spectrum of bromine? A. Graph A B. Graph B C. Graph C D. Graph D

The diagrams show the 3s and 3p sublevels of a sulfur atom; the inner sublevels are full. Which diagram represents the ground-state electron configuration, in agreement with the Pauli exclusion principle and Hund's rule? A. Diagram A B. Diagram B C. Diagram C…

4.06 g of hydrated magnesium chloride, $\ce{MgCl2*6H2O}$ ($M_\mathrm{r}$ = 203), is dissolved in water to make 0.250 $\mathrm{dm^3}$ of solution. What is the concentration of chloride ions, in $\mathrm{mol\,dm^{-3}}$, in this solution? A. 0.0400 B. 0.0800 C.…

Under which conditions does the gas behave most like an ideal gas? A. Helium at 200 kPa and 300 K B. Helium at 20 kPa and 600 K C. Sulfur dioxide at 20 kPa and 600 K D. Sulfur dioxide at 200 kPa and 300 K

Part of the lattice of potassium bromide, KBr, is shown in an expanded view. Which statement about the lattice of potassium bromide is correct? A. Each bromide ion is in contact with six potassium ions. B. Neighbouring ions are held together by shared pairs of…

What are the electron domain geometry and the molecular geometry of the $\ce{BrF4-}$ ion? A. Electron domain geometry: tetrahedral; molecular geometry: tetrahedral B. Electron domain geometry: trigonal bipyramidal; molecular geometry: seesaw C. Electron domain…

Which orbitals overlap to form the $\sigma$-bond and the two $\pi$-bonds between carbon and nitrogen in hydrogen cyanide, HCN? A. $\sigma$-bond: sp and $\mathrm{sp^3}$; $\pi$-bonds: p and p B. $\sigma$-bond: sp and sp; $\pi$-bonds: p and p C. $\sigma$-bond: sp…

Which species contain a coordination bond? I. $\ce{CO}$ II. $\ce{H3O+}$ III. $\ce{BF3}$ A. I and II only B. I and III only C. II and III only D. I, II and III

Which Lewis formula of the sulfate ion, $\ce{SO4^2-}$, is preferred on the basis of formal charges? A. Formula A B. Formula B C. Formula C D. Formula D

Which statement best explains why aluminium can be drawn into thin wires? A. The delocalized electrons carry charge through the metal. B. The layers of aluminium ions can slide over each other while the delocalized electrons keep the lattice bonded. C.…

Which substance is a good conductor of electricity in the solid state? A. Graphene B. Diamond C. Silicon dioxide D. Silicon

What is the IUPAC name of the compound shown? A. 3-methylhexan-4-one B. 4-methylhexan-3-one C. 4-ethylpentan-3-one D. 2-ethylpentan-3-one

What are the oxidation states of the elements in $\ce{K2MnO4}$? A. K: +1, Mn: +6, O: −2 B. K: +1, Mn: +7, O: −2 C. K: +2, Mn: +4, O: −2 D. K: +1, Mn: +6, O: −1

Which statement is correct for the group 17 elements from chlorine to iodine? A. The first ionization energy of the elements decreases. B. The elements become stronger oxidizing agents. C. The elements become more volatile. D. The radius of the halide ion…

Which ion is likely to form a coloured aqueous solution, based on its electron configuration? A. $\ce{Ag+}$ B. $\ce{Ti^4+}$ C. $\ce{Cd^2+}$ D. $\ce{Cr^3+}$

Which molecule contains a chiral centre? A. $\ce{CH3CH(NH2)COOH}$ B. $\ce{(CH3)2CHCOOH}$ C. $\ce{CH3CH2CH(CH3)CH2CH3}$ D. $\ce{ClCH2CH(OH)CH2Cl}$

Which is the low-resolution $\ce{^1H}$ NMR spectrum of methyl methanoate, $\ce{HCOOCH3}$? A. Spectrum A B. Spectrum B C. Spectrum C D. Spectrum D

Which pair of compounds correctly illustrates the stated type of isomerism? A. Positional isomerism: $\ce{CH3CH2CHO}$ and $\ce{CH3COCH3}$ B. Functional group isomerism: $\ce{CH3CH2CH2CH2OH}$ and $\ce{CH3CH(OH)CH2CH3}$ C. Cis-trans isomerism: the two compounds…

The potential energy profile of a reaction is shown. Which reaction has this energy profile? A. $\ce{Cl2(g) -> 2Cl(g)}$ B. $\ce{CaCO3(s) -> CaO(s) + CO2(g)}$ C. $\ce{N2O4(g) -> 2NO2(g)}$ D. $\ce{2Mg(s) + O2(g) -> 2MgO(s)}$

What is the enthalpy change, in $\mathrm{kJ\,mol^{-1}}$, for the formation of methanol from carbon monoxide and hydrogen? $\ce{CO(g) + 2H2(g) -> CH3OH(l)}$ Substance $\Delta H_\mathrm{c}^\ominus$ / $\mathrm{kJ\,mol^{-1}}$ $\ce{CO(g)}$ −283 $\ce{H2(g)}$ −286…

Which equation represents the enthalpy change of atomization, $\Delta H_\mathrm{at}$, of iodine? A. $\ce{I2(s) -> I2(g)}$ B. $\ce{I2(g) -> 2I(g)}$ C. $\ce{1/2I2(g) -> I(g)}$ D. $\ce{1/2I2(s) -> I(g)}$

Which statement best describes an environmental consequence of using fossil fuels? A. The carbon dioxide released is completely absorbed by the oceans, so its concentration in the atmosphere does not change. B. Coal has a higher hydrogen to carbon ratio than…

Which reaction is expected to have the largest decrease in entropy? A. $\ce{2H2S(g) + SO2(g) -> 3S(s) + 2H2O(l)}$ B. $\ce{2C4H10(g) + 13O2(g) -> 8CO2(g) + 10H2O(l)}$ C. $\ce{4NH3(g) + 5O2(g) -> 4NO(g) + 6H2O(g)}$ D. $\ce{2CO(g) + O2(g) -> 2CO2(g)}$

Equal volumes of the gases $\ce{Q2}$ and $\ce{R2}$ are mixed in a sealed container and react until one of them is used up, forming the gas $\ce{QR2}$. The volume of $\ce{QR2}$ formed, measured under the same conditions, is 50 $\mathrm{cm^3}$.…

What volume of hydrogen, in $\mathrm{cm^3}$, is produced at STP when 0.810 g of aluminium reacts with an excess of hydrochloric acid? $\ce{2Al(s) + 6HCl(aq) -> 2AlCl3(aq) + 3H2(g)}$ Molar volume of an ideal gas at STP = 22.7 $\mathrm{dm^3\,mol^{-1}}$ A. 341 B.…

The dotted line shows the volume of hydrogen produced when an excess of magnesium ribbon is added to 50 $\mathrm{cm^3}$ of 2.0 $\mathrm{mol\,dm^{-3}}$ hydrochloric acid. Which curve shows the volume of hydrogen produced when the same excess of magnesium ribbon…

Which reaction has the lowest activation energy? A. $\ce{HBr(g) -> H(g) + Br(g)}$ B. $\ce{2Cl(g) -> Cl2(g)}$ C. $\ce{CH4(g) + Cl(g) -> CH3(g) + HCl(g)}$ D. $\ce{HBr(g) -> H+(g) + Br-(g)}$

The reaction $\ce{2P -> S + T}$ was studied by measuring the initial rate at different initial concentrations of P. Which graph shows that the reaction is first order with respect to P? A. Graph A B. Graph B C. Graph C D. Graph D

Which statement explains why a chemical equilibrium is described as dynamic? A. The forward and reverse reactions continue to take place at equal rates. B. The concentrations of the reactants and products keep changing until the reaction stops. C. The position…

Nitrogen reacts with hydrogen to form ammonia. $\ce{N2(g) + 3H2(g) <=> 2NH3(g)}$ A mixture of 1.50 mol of $\ce{N2(g)}$ and 4.20 mol of $\ce{H2(g)}$ was placed in a 1.00 $\mathrm{dm^3}$ container at a certain temperature. At equilibrium the mixture contained…

In which reaction does water behave as a Brønsted–Lowry acid? A. $\ce{H2O(l) + HCl(g) -> H3O+(aq) + Cl-(aq)}$ B. $\ce{H2O(g) + SO3(g) -> H2SO4(l)}$ C. $\ce{2H2O(l) -> 2H2(g) + O2(g)}$ D. $\ce{H2O(l) + NH3(aq) -> NH4+(aq) + OH-(aq)}$

Which aqueous solution has the highest pH? A. 0.010 $\mathrm{mol\,dm^{-3}}$ $\ce{KNO3}$ B. 0.010 $\mathrm{mol\,dm^{-3}}$ $\ce{NH4NO3}$ C. 0.010 $\mathrm{mol\,dm^{-3}}$ $\ce{CH3COONa}$ D. 0.010 $\mathrm{mol\,dm^{-3}}$ $\ce{NaHSO4}$

Which half-equation represents the reduction of sulfuric acid to sulfur dioxide in acidic solution? A. $\ce{H2SO4 + 2H+ + 2e- -> SO2 + 2H2O}$ B. $\ce{H2SO4 + 4H+ + 4e- -> SO2 + 2H2O}$ C. $\ce{H2SO4 + 2H2O -> SO2 + 6H+ + 2e-}$ D.…

Which compounds are oxidized when heated with acidified potassium dichromate(VI) solution? I. $\ce{CH3CH2C(CH3)2OH}$ II. $\ce{(CH3)2CHCH2OH}$ III. $\ce{CH3CH(OH)CH3}$ A. I and II only B. I and III only C. II and III only D. I, II and III

A student placed strips of the metals L, M and N in aqueous solutions containing the ions $\ce{M^2+}$, $\ce{N^2+}$ and $\ce{L^2+}$ respectively, as shown. The observations are given under each beaker. What is the order of increasing reactivity of the three…

Which radical is most likely to form when one covalent bond in bromochlorodifluoromethane, $\ce{CBrClF2}$, is broken by ultraviolet light in the upper atmosphere? A. •$\ce{CBrF2}$ B. •$\ce{CClF2}$ C. •$\ce{CBrClF}$ D. •$\ce{CBrClF2}$

Pent-2-ene undergoes a range of addition reactions. Which reagent and product are correctly matched? A. Reagent $\ce{H2}$, product pent-1-ene B. Reagent $\ce{Br2}$, product 2,3-dibromopentane C. Reagent $\ce{H2O}$, product pentan-1-ol D. Reagent $\ce{HBr}$,…

Which statements are correct for the complex ion $\ce{[CoCl4]^2-}$? I. The oxidation state of cobalt is +4. II. The chloride ions act as Lewis bases. III. The coordination number of cobalt is 4. A. I and II only B. I and III only C. II and III only D. I, II…

Which statement is correct about an $\mathrm{S_N1}$ mechanism? A. The rate of reaction depends on the concentrations of both the halogenoalkane and the nucleophile. B. The rate-determining step forms a carbocation intermediate from a single molecule. C. The…