Chemistry Paper 3B WASSCE (SC), 2023

Question 2B

 

G is an inorganic salt. Carry out the following exercises on G

           Record your observations and identify any gas(es) evolved.
State the conclusions you draw from the results of each test.

(a) Dissolve all of G in about 10 cm3 of distilled water in a boiling tube    

 

(b) (i)         Test the resulting solution with litmus paper.
(ii)        To about 2 cm3 portion of the solution in a test tube, add NaOH(aq). Then   
warm the resulting mixture gently.
(iii)       To another 2 cm3 portion of the solution, add dilute HNO3.
(Iv)      To 2cm3 portion of the solution, add BaCl2(aq) followed by excess dilute HNO3.

 

Observation

 

The performance of the candidates was below average in this question.

In part (a), majority of the candidates dissolved G in about 10 cm3 of distilled water in a boiling tube.

In part (b), majority of the candidates did not adhere to the instructions, and this affected their performance.

The expected answers include:

 

TEST

OBSERVATION

INFERENCE

(a)

G + distilled water

Colourless solution obtained

 

 

  

(b)

Solution of G + litmus papers

Turn red litmus blue

 

G(aq) is alkaline/ basic

(c)

Solution of G + NaOH(aq)
Mixture warmed

 
No precipitate formed / no visible reaction
Colourless gas with pungent /chocking / irritating smell  evolved
Gas turned red litmus paper
to blue / formed dense white fumes with conc HCl  

 

 

 

 

Gas is NH3 from NH4+

(i)

Solution of G + HNO3(aq)

Effervescence, gas evolved
colourless, odourless
Gas turned lime water milky

 

Gas is CO2 from
CO32-/ HCO3- present
 

(ii)

Solution of G + BaCl2(aq)
+ HNO3(aq)

White (Chalky) precipitate formed
Precipitate dissolved (with rapid effervescence)

 CO32- SO32- SO42-

CO32- present