TEST OF PRACTICAL KNOWLEDGE QUESTION (a) A zinc salt, E when heated strongly, produced a brown gas with pungent smell, a colourless gas that rekindled a glo...

TEST OF PRACTICAL KNOWLEDGE QUESTION

(a) A zinc salt, E when heated strongly, produced a brown gas with pungent smell, a colourless gas that rekindled a glowing splint, and a residue that was allowed to cool.

(i) identify the salt E.

(ii) Write an equation for the decomposition of E.

(iii) State what would be observed when the residue was allowed to cool.

(b) Describe how 250cm\(^3\) of 0.2 mol dm\(^3\) H\(_2\)SO\(_4\) could be prepared from 150 cm\(^3\) of a 1.0 mol dm\(^{3}\) stock solution of the acid.

(c) State the effect of aqueous solution of Al\(_2(SO_4)_3\) on litmus paper.

Answer Details

(a)

1. (i) The salt E is likely to be Zinc sulfide (ZnS).
2. (ii) The equation for the decomposition of Zinc sulfide (ZnS) is:
   2 ZnS (s) -> 2 Zn (s) + S₈ (g)
3. (iii) When the residue is allowed to cool, a white solid would be observed. This solid would be Zinc (Zn).

(b)

To prepare 250cm³ of 0.2 mol dm³ H₂SO₄ from 150 cm³ of a 1.0 mol dm³ stock solution of the acid, you would need to dilute the stock solution. You can do this by adding 150 cm³ of the 1.0 mol dm³ stock solution to an equal amount of water, which would give you 300 cm³ of a 0.5 mol dm³ solution. Then, you could add 50 cm³ more of water to the solution, which would give you a final volume of 350 cm³ of a 0.2 mol dm³ solution of H₂SO₄.

(c)

The aqueous solution of Al₂(SO₄)₃ has a neutral effect on litmus paper. It does not turn red litmus paper blue or blue litmus paper red, indicating that it is a neutral solution.