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2018 WAEC Chemistry Practical All your burette readings (initials and final) as well as the size of your pipette...

Chemistry
WAEC 2018

All your burette readings (initials and final) as well as the size of your pipette must be recorded but no account of experimental procedure is required. All calculations must be done in your booklet.

C and D are inorganic salts. Carry out the following exercises on them. Record your observations and identify any gas(es) evolved. State the conclusions you draw from the result of each test.

(a) Put all of C in a test tube and add about 5 cm of distilled water. Shake thoroughly and test the resulting solution with Litmus paper. Divide the solution into three portions.

(i) To the first portion, add NaOH\(_{(aq)}\) in drops, then in excess.

(ii) To the second portion. add NH\(_{3(aq)}\) in drops. then in excess.

(iii) To the third portion. add AgNO\(_{3 (aq)}\) followed by HCl\(_{(aq)}\)

 

 (b)(i) Put all of D in a test tube and add about 5 cm\(^3\) of distilled water. Shakę thoroughly and feel the test tube.

(ii) To about 2 cm\(^3\) of the solution, add HCl\(_{(aq)}\)

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Explanation
TEST OBSERVATION INTERFERENCE

(a) Sample C + distilled water + shaking 

Resulting solution + litmus paper 

Sample C dissolved to form a blue/greenish solution 

Solution turns blue litmus paper red

Solution is acidic 

(I) 1st portion + NaOH\(_{(aq)}\) in drops

Then in excess 

Blue precipitate formed 

Precipitate insoluble in excess

Cu\(^{2+}\) is present

(ii) 2nd portion NH\(_4\)OH\(_{(aq)}\) in drops 

Then in excess

Light blue precipitate formed 

Precipitate dissolve in excess to form a deep blue solution 

Cu\(^{2+}\) is confirmed 
(iii) 3rd portion + AgNO\(_{3(aq)}\)+ NCl\(_{(aq)}\)

White precipitate formed 

Precipitate insoluble 

Cl\(^{-1}\) or CO\(_{3^{2-}}\) or S\(^{2-}\) or SO\(_3^2\)

Cl\(^{2-}\) is present

(b)(i) Sample D + distilled water touching or feeling the test tubes 

Sample D dissolved to form a colourless solution 

Test tube feels cold on touching 

 

 

Dissolution is endothermic

(ii) D\(_{(aq)}\) = HCl\(_{(aq)}\)

Effervescence (bubbling) occurs, a colourless, odourless gad evolved 

Gas turned lime water milky 

CO\(_{2(g)}\) from CO\(_{3^{2-}}\) or HCO\(_3^-\)

 


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NECO June/July 2024 - Get offline past questions & answers - Download objective & theory, all in one app 48789
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NECO June/July 2024 - Get offline past questions & answers - Download objective & theory, all in one app 48789