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Chemistry 1991 WAEC Past Questions

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51

A is a solution containing 0.50 mole of barium chloride per dm\(^3\). Solution B contains 1.0 mole of tricxocarbonate (IV) salt per dm\(^3\)

(a) State what would be observed and give the confirmatory test for any gases evolved if the following tests were performed

(i) mixing 2cm\(^3\) each of solutions A and B in a test tube

(ii) adding excess dilute hydrochloric acid to the mixture from (a)(i) above

 

(b) 10cm\(^3\) of solution A were measured into each of seven boiling tubes of uniform bore and various quantities of solution B were added respectively to the boiling tubes, The tubes were immersed in hot water. After the reaction, the height of the product in each of the tubes was measured. The results were as tabulated below.

Test tube  I II III IV V VI VII
Volume of sodium B added (cm\(^3\)) 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Height of the product (to the nearest m) 12 18 24 30 30 30 30

 

(i) Plot a graph of the height of the product against the volume of solution B added to each test tube. Explain the shape of the graph

(ii) Calculate the amount (in mole) of the trioxocarbonate (IV) salt contained in the volume of solution B added to tube lV

(iii) Calculate the amount (in mole) of barium chloride contained in 10cm\(^3\) of solution A. Hence, determine the mole ratio of barium chloride and the trioxocarbonate (IV) Salt in the reaction

View Answer & Discuss WAEC 1991
52

C is a mixture of an organic and an inorganic salt. The test recorded in the table below were performed as indicated, 

(a)Copy and complete the table as appropriate. 

Test  Observation Inference
(i) C + water mixed thoroughly and filtered Partially soluble, colourless filtrate, white residue  

(ii) Portion of filtrate from (i) + NH\(_{3(aq)}\) in drops, then in excess 

White precipitate which dissolves in excess to give a colourless solution   
(iii) Portion of filtrate from (i) + NH\(_3\) in drops, then in excess White precipitate insoluble in excess   
(iv) Portion of filtrate from (i) + conc. HCl + heat  White precipitate which dissolves on warming and reappears on cooling   
(v) Portion of filtrate from (i) + conc. H\(_2\)SO\(_4\) + gentle warming Brown fumes produced on warming   
(vi) Residue from (i) + iodine solution  Blue-black colouration    
(vii) Residue from (i) + Fehling's solution + heat     
(vii) Residue from (i) + dil HCl  solution + heat + Fehling's solution     

 

(b) From the information provided and your inference, identify the compounds of C 

(c) Describe the action of heat on a solid sample of the inorganic component  Write an equation for the reaction.

(d) State what would be observed if an aqueous suspension of the organic component were heated to boiling 

View Answer & Discuss WAEC 1991
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