K.C.S.E Chemistry Q & A-MODEL 2017.PP2.Q N.4

23/11/2020

KCSE Chemistry 2017 Topical Questions and Answers

All Questions Featuring Chemistry Form 1, Form 2, Form 3, Form 4, Paper 1, Paper 2 and Paper 3

W is a colourless aqueous solution with the following properties:

I It turns blue litmus paper red.
II On addition of cleaned magnesium ribbon, it gives off a gas that burns with a pop sound.
III On addition of powered sodium carbonate, it gives off a gas which forms a precipitate with calcium hydroxide solution.
IV When warmed with copper(II) oxide powder, a blue solution is obtained but no gas is given off
V On addition of aqueous barium chloride, a white precipitate is obtained.

(a) (i) State what properties (I) and (III) indicate about the nature of W.
(ii) Give the identity of W.
(iii) Name the colourless solution formed in (II) and (III).
(iv) Write an ionic equation for the reaction indicated in (V).
(b) Element V conducts electricity and melts at 933K. When chlorine gas is passed over heated V, it forms a vapour that solidifies on cooling. The solid chloride dissolves in water to form an acidic
solution. The chloride vapour has a relative molecular mass of 267 and contains 19.75% of V. At a higher temperature, it dissociates to a compound of relative molecular mass 133.5. When aqueous
sodium hydroxide is added to the aqueous solution of the chloride, a white precipitate is formed which dissolves in excess alkali. (V = 27.0 ; CI = 35.5)
(i) Determine the:

I empirical formula
II molecular formula

(ii) Draw the structure of the chloride vapour and label the bonds.
(iii) Write an equation for the reaction that form a white precipitate with sodium hydroxide.

ANSWERS