Chemistry HL Paper 1A, May 2026

What is correct about the species $\ce{^{65}Zn^{2+}}$? A. 65 protons, 65 neutrons, 63 electrons B. 30 protons, 35 neutrons, 28 electrons C. 30 protons, 65 neutrons, 28 electrons D. 65 protons, 35 neutrons, 63 electrons

What will be the volume of 4.00 dm3 of gas that has had the pressure decreased from 150 kPa to 50.0 kPa, and its temperature increased from 27.0 °C to 127 °C? A. 16.0 dm3 B. 12.0 dm3 C. 56.4 dm3 D. 1.78 dm3

What is the correct electron configuration of the selenium atom? A. $1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^4$ B. $1s^2 2s^2 2p^6 2d^{10} 3s^2 3p^6 4s^2 4p^4$ C. $1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^6$ D. $1s^2 2s^2 2p^6 3s^2 3p^6 3d^{8} 4s^2 4p^6$

Successive ionization energies of an element: Ionization energy number Energy / kJ mol⁻¹ 1st 738 2nd 1451 3rd 7733 4th 10 540 5th 13 630 6th 17 995 7th 21 704 8th 25 656 9th 31 643 10th 35 461 Which element has these successive ionization energies? A. Sodium…

How many ions are present in 142 g of $\ce{Na2SO4}$? $M(\ce{Na2SO4}) = 142\ \mathrm{g\,mol^{-1}}$ A. 1 B. 3 C. $6.02 \times 10^{23}$ D. $1.81 \times 10^{24}$

What is the empirical formula of an alcohol with 60.0 % mass carbon and 13.4 % mass hydrogen? A. $\ce{C3H7}$ B. $\ce{C6H16O2}$ C. $\ce{C3H8O}$ D. $\ce{C2H6O}$

Which properties are expected for the compound lithium bromide? A. Not soluble in water, low melting point, does not conduct electricity when solid, does not conduct electricity when molten B. Not soluble in water, low melting point, conducts electricity when…

What is the correct electron domain geometry and molecular geometry of $\ce{SF4}$? A. Trigonal bipyramidal electron domain geometry, trigonal bipyramidal molecular geometry B. Trigonal bipyramidal electron domain geometry, seesaw molecular geometry C.…

Which species contains a coordination bond? A. $\ce{AlCl3}$ B. $\ce{PH3}$ C. $\ce{[NH4]+}$ D. $\ce{HCOO-}$

Which molecules are polar? I. $\ce{CHCl3}$ II. $\ce{CH2F2}$ III. $\ce{CF4}$ A. I and II only B. I and III only C. II and III only D. I, II and III

How many sigma and pi bonds are present in pent-1-yne, $\ce{C5H8}$? A. 12 sigma bonds and 2 pi bonds B. 8 sigma bonds and 3 pi bonds C. 13 sigma bonds and 1 pi bond D. 9 sigma bonds and 4 pi bonds

Which classification is correct? A. Alkali metal: rubidium; transition element: platinum; halogen: xenon; noble gas: bromine B. Alkali metal: rubidium; transition element: platinum; halogen: bromine; noble gas: xenon C. Alkali metal: platinum; transition…

Which oxide will react with water to produce the most basic solution? A. Potassium oxide B. Calcium oxide C. Sulfur trioxide D. Nitrogen dioxide

Which functional groups are present in this molecule? A. Secondary amine, hydroxyl, alkoxy B. Tertiary amine, alcohol, ketone C. Tertiary amine, hydroxyl, alkoxy D. Secondary amine, alcohol, ketone

Which of these molecules are isomers of each other? I. Butanal II. 2-methylpropan-1-ol III. Butan-2-ol A. I and II only B. I and III only C. II and III only D. I, II and III

The table shows the observed colour of three octahedral complex ions formed by the same metal ion, $\ce{M^{2+}}$, with different ligands. Complex ion Colour of complex $\ce{[MF6]^4-}$ green $\ce{[M(H2O)6]^2+}$ blue $\ce{[M(NH3)6]^2+}$ yellow Which statement…

Which molecules exhibit cis-trans isomerism? I. Pent-2-ene II. 1,1-dichloroethene III. 1,2-dibromoethene A. I and II only B. I and III only C. II and III only D. I, II and III

Which compound could produce this mass spectrum? Mass lost (Mr) Possible neutral fragment lost 15 •CH3 18 H2O 28 CH2=CH2 or CO 29 •CH2CH3 or •CHO 45 •COOH A. Butanone B. Butanal C. Butan-1-ol D. Butan-2-ol

Which classification is correct for this reaction? $\ce{2Mg(s) + CO2(g) -> 2MgO(s) + C(s)}$, heat is released A. Endothermic; temperature decreases; reactants more stable B. Exothermic; temperature decreases; products more stable C. Exothermic; temperature…

What is the sum of the coefficients when this equation is balanced with the smallest whole numbers? $\ce{\_CH3CH(CH3)CH2CH2CH3 + \_O2 -> \_CO2 + \_H2O}$ A. 20 B. 37 C. 47 D. 53

Given the following data: $\ce{CaO(s) + CO2(g) -> CaCO3(s)}$ $\Delta H = -p\ \mathrm{kJ}$ $\ce{2Ca(s) + O2(g) -> 2CaO(s)}$ $\Delta H = -q\ \mathrm{kJ}$ $\ce{2CaCO3(s) -> 2Ca(s) + 2C(s) + 3O2(g)}$ $\Delta H = +r\ \mathrm{kJ}$ What is the $\Delta H$ of the…

In which reaction will there be a decrease in entropy? A. $\ce{NH4NO3(s) -> NH4NO3(aq)}$ B. $\ce{CaCO3(s) -> CaO(s) + CO2(g)}$ C. $\ce{2H2(g) + O2(g) -> 2H2O(l)}$ D. $\ce{Zn(s) + CuSO4(aq) -> ZnSO4(aq) + Cu(s)}$

What is the effect of decreasing temperature on this Maxwell-Boltzmann energy distribution curve? A. The curve maximum is higher and to the left of A. B. The curve maximum is lower and to the right of A. C. The curve maximum is higher and to the right of A. D.…

Which volume of oxygen is required to react fully with 40.0 cm3 of butane to ensure complete combustion? $\ce{2C4H10(g) + 13O2(g) -> 8CO2(g) + 10H2O(g)}$ A. 520 cm3 B. 260 cm3 C. 130 cm3 D. 40.0 cm3

Which substances will be present in the reaction vessel at the end of the reaction between 1.5 g of magnesium and 50.0 cm3 of 1.0 mol dm⁻³ hydrochloric acid? $\ce{Mg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g)}$ A. $\ce{HCl(aq)}$, $\ce{MgCl2(aq)}$ B. $\ce{Mg(s)}$,…

Which of these changes will increase the time taken for this reaction to go to completion? $\ce{Zn(s) + H2SO4(aq) -> ZnSO4(aq) + H2(g)}$ A. Increase the temperature B. Increase the concentration of $\ce{H2SO4}$ C. Use powdered zinc instead of zinc granules D.…

Which change would shift the position of this equilibrium towards the products? $\ce{H2(g) + I2(g) <=> 2HI(g)}$ $\Delta H = -9\ \mathrm{kJ\,mol^{-1}}$ A. Increase pressure B. Decrease pressure C. Increase temperature D. Decrease temperature

What can be deduced about this equilibrium reaction from these data? $\ce{A(g) + B(g) <=> 2C(g)}$ Temperature / K Equilibrium constant, K 280 400 340 40.0 A. It is an exothermic reaction and [products] < [reactants] at equilibrium. B. It is an endothermic…

What does the pre-exponential (Arrhenius) factor, A, represent in the Arrhenius equation $k = Ae^{-E_a/RT}$? A. The fraction of collisions with the correct orientation and sufficient frequency B. The activation energy of the reaction C. The overall rate…

Which combination of substances is correctly used for electroplating an iron object with tin using an electrolytic cell? A. X: tin, Y: iron, Z: tin(II) sulfate solution B. X: iron, Y: tin, Z: tin(II) sulfate solution C. X: tin, Y: iron, Z: iron(II) sulfate…

Which of these salts, when dissolved in water to make solutions of equal concentration, has the highest pH? A. $\ce{KCl}$ B. $\ce{NaHCO3}$ C. $\ce{NH4Br}$ D. $\ce{NH4HCO3}$

Which statement about this reaction is correct? $\ce{2Cl2 + O2 -> 2Cl2O}$ A. Chlorine is the reducing agent. B. Oxygen is the reducing agent. C. Chlorine is reduced. D. Oxygen is oxidized.

Which of these reactions will occur spontaneously? I. $\ce{KI + Br2}$ II. $\ce{KBr + Cl2}$ III. $\ce{KCl + Br2}$ A. I and II only B. I and III only C. II and III only D. I, II and III

Which combination is correct for this cell, when nickel is more reactive than silver? A. Cathode: silver; anode: nickel; sign on cathode: -; sign on anode: + B. Cathode: nickel; anode: silver; sign on cathode: -; sign on anode: + C. Cathode: nickel; anode:…

Which products are produced at the electrodes by the electrolysis of aqueous sodium iodide? A. Product at cathode: sodium; product at anode: iodine B. Product at cathode: hydrogen; product at anode: iodine C. Product at cathode: iodine; product at anode:…

Which statement explains the Lewis acid-base nature of the carbocation in this reaction? $\ce{C2H5+ + I- -> C2H5I}$ A. Lewis base because it accepts a pair of electrons B. Lewis base because it donates a pair of electrons C. Lewis acid because it donates a…

Which equation shows the first species acting as an electrophile? A. $\ce{Br- + CH3CH2+ -> CH3CH2Br}$ B. $\ce{H2O + H+ -> H3O+}$ C. $\ce{CN- + CH3Br -> CH3CN + Br-}$ D. $\ce{AlCl3 + Cl- -> AlCl4-}$

What can react with benzene to produce nitrobenzene? A. $\ce{NO2}$ B. $\ce{NO3-}$ C. $\ce{NO2+}$ D. $\ce{NO+}$

Which reaction will be fastest when a halogen is substituted by aqueous hydroxide ions? A. $\ce{(CH3)2C(F)CH2CH2CH3}$ B. $\ce{(CH3)2C(Cl)CH2CH2CH3}$ C. $\ce{(CH3)2C(Br)CH2CH2CH3}$ D. $\ce{(CH3)2C(I)CH2CH2CH3}$

What is the charge on this complex ion of chromium(III), $\ce{[Cr(H2O)4Cl2]^{x}}$? A. 1+ B. 3+ C. 5+ D. 1-