CIE iGCSE Co-Ordinated Science C9.4 Reactivity series Exam Style Questions Paper 4
Question
(a) Magnesium sulfate contains magnesium ions, Mg2+, and sulfate ions, \( SO_{4}^{2-}\) .
(i) Determine the formula of magnesium sulfate.
formula = …………………………………………………
(ii) Explain why solid magnesium sulfate cannot conduct electricity but solid magnesium can conduct electricity.
(b) Magnesium reacts with hydrochloric acid, HCl.
Magnesium chloride, MgCl2, and hydrogen gas are made.
(i) Describe the test for hydrogen gas and the observation for a positive result.
test …………………………………………………………………………………
observation ……………………………………………………………………..
(ii) Calculate the mass of magnesium chloride made when 1.2g of magnesium reacts with excess hydrochloric acid.
Mg + 2HCl → MgCl2 + H2
[Ar : Cl, 35.5; H, 1; Mg, 24]
(iii) The ionic equation for this reaction is shown.
Mg + 2H+ → Mg2+ + H2
Explain why this reaction is described as a redox reaction.
▶️Answer/Explanation
Ans :
2(a)(i) MgSO4 ;
2(a)(ii) magnesium:
idea that magnesium has electrons ;
(electrons) can move ;
magnesium sulfate:
idea of that ions are held in fixed positions (in a solid) ;
2(b)(i) test – lighted splint ;
result – (squeaky) pop ;
2(b)(ii) relative molecular mass of MgCl2 = 95 ;
\(\frac{9.5 \times 1.2}{24} =4.8(g)\)
2(b)(iii) EITHER
Mg/magnesium is oxidised ;
H+ / hydrogen ions are reduced ;
OR
the Mg / magnesium atoms lose electrons ;
H+ / hydrogen ions gain electrons ;