Zadanie 2b, Paper 2, maj 2025, TZ2, Chemia IB SL

(i) Covalent bonds between: S and O «within the sulfate ion» ✔

Ionic bonds between: Ga³⁺ and SO₄²⁻ ✔

(ii) in a covalent bond the valence electrons are shared between the atoms, whereas in an ionic bond they are transferred from one atom to another ✔

(iii) 2 Ga(OH)₃(s) + 3 H₂SO₄(aq) → Ga₂(SO₄)₃(aq) + 6 H₂O(l)

correct formulas of the products ✔

correctly balanced equation ✔

(iv) M(Ga(OH)₃) = 69.72 + 3(16.00 + 1.01) = 120.75 «g mol⁻¹»; $n(\ce{Ga(OH)3}) = \dfrac{6.04}{120.75} = 0.0500$ «mol» ✔

$n(\ce{H2SO4}) = \dfrac{3}{2} \times 0.0500 = 0.0750$ «mol» ✔

$V = \dfrac{0.0750}{1.50} = 0.0500$ «dm³» / 50.0 «cm³» ✔

(v) yes AND gallium is in the same group as aluminium, whose hydroxide and oxide are amphoteric «Ga(OH)₃ reacts with both acids and alkalis» ✔

(vi) place a piece of gallium in aqueous nickel(II) sulfate «or a piece of nickel in aqueous gallium(III) sulfate» ✔

a deposit of nickel «and fading of the green colour» shows that gallium is the more reactive metal / no change when nickel is placed in gallium(III) sulfate shows that nickel is the less reactive metal ✔

(i) [2] one mark for each pair of particles. (ii) [1] sharing contrasted with transfer; accept 'gain and loss' for transfer. (iii) [2] M1 correct formulas of gallium(III) sulfate and water; M2 balanced. (iv) [3] M1 amount of gallium(III) hydroxide; M2 amount of acid from the 2:3 ratio; M3 volume; award [3] for a correct final answer; ECF from M1 and M2. (v) [1] the prediction must be justified by the position of gallium below aluminium in group 13. (vi) [2] M1 a valid displacement experiment; M2 how the observation is interpreted.