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1988 WAEC Chemistry Practical Carry out the following exercises on sample C. Record your observations and identify any gases...

Chemistry
WAEC 1988

Carry out the following exercises on sample C. Record your observations and identify any gases evolved. State the conclusion you draw from the result of each test.

(a) Put about half of sample C into a conical flask and add about 5cm\(^3\) of tetrachloroethane followed by 15cm\(^3\) of water. Shake vigorously for about one minute. Put the resulting mixture into a burette and allow to stand until two layers separate. Run the two layers into two separate conical flasks and label them accordingly.

(b) Using the following reagents only, bench sodium hydroxide solution, aqueous ammonia solution, aqueous lead (II) trioxonite (V) solution, silver trioxonitrate (V) solution. bench trioxonitrate (V) acid. Identify the ions present in the upper layer solution

(c) Add 2 - 3 drops of the lower layer solution to about 2cm\(^3\) of starch solution from your result, name the substances which dissolved in the upper and lower layers. 

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Explanation
 Test  Observation Inference 

(a) C + CCl\(_4\)  water, shaken vigorously and mixture put in a burette 

(b)(i) A portion of upper layer + aq. NaOH solution 

(iii) Another portion of upper layer + pb(NO\(_3\))\(_2\) + dil. HNO\(_3\) 

(iv) Another portion of upper layer + AgNO\(_3\) + HNO\(_3\)

(c) 2 - 3 drops of lower layer + starch solution 

 

Two immiscible layers separate with a blue aqueous in the upper lower layer.

Blue ppt. insoluble in excess of aq. NaOH solution 

Blue ppt. insoluble in excess of aq. NH\(_3\) solution to form a deep blue solution 

White precipitate is formed 

No. ppt. 

Blue-black solution  

C is a mixture of 2 substances 

Cu\(^{2+}\) present 

Cu\(^{2+}\) confirmed

Cl\(^{-}\) or SO\(_4^{2-}\) present 

Cl\(^{-}\) absent 

SO\(^{2-}_4\) present 

iodine present 

 

C is a mixture of copper (II) tetraoxosulphate (VI) and iodine 


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