Chemistry Past Questions and Answers

In which of the following is the oxidation number of sulphur equal to -2?

A SO₃
B S₈
C H₂S
D SO₂

Question 42:

In the electrolysis of CuSO_4(g) using platinum electrodes, the reaction at the anode is

A 4H⁺ + 4e^- â†’ 2H₂
B 4OH^- - 4e^- → 2H₂O + O₂
C 2OH - 2e^- â†’ 2OH
D 2OH^- + 2OH^- â†’ 2H₂O + O₂

Question 43:

Na2CO3(g) + 2HCl(aq) â†’ 2NaCl(aq) + H2O(l) + CO2(g)
How many moles of sodium trioxocarbonate (IV) are there in a 25 cm3 solution which required 10cm3 of 0.05 mol dm-3 hydrochloric acid solution to neutralize it?

A 1.000 mole
B 0.100 mole
C 0.010 mole`
D 0.111 mole

Question 44:

If the heat of combustion of hydrogen is -285.8kJ,
What is the heat of formation of water?

A +571.6 kJ
B -571.6 kJ
C -285.8 kJ
D +285.8 kJ

Question 45:

5SO_2(g) + 2KMnO_4(aq) + 2H₂O_(l) â†’ K₂SO₄ + 2MnSO_4(aq) + 2H₂SO_4(aq)
In the reaction above, the products give a

A Purple solution
B Purple precipitate
C Colourless precipitate
D Colourless solution