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2009 WAEC Chemistry Practical Credit will be given for strict adherence to the instructions, for observations precisely recorded and...

Chemistry
WAEC 2009

Credit will be given for strict adherence to the instructions, for observations precisely recorded and for accurate inferences. All tests, observations and inferences must be clearly entered in your answer book in ink, at the time they are made.

C is a mixture of two salts. Carry out the following exercises on C. Record your observations and identify any gas(es) evolved. State the conclusion you draw from the result of each test.

(a) Put all of C in a test tube and add about 10 cm\(^3\) of distilled water. Shake thoroughly and filter. Keep both the filtrate and the residue. Divide the filtrate into three portions.

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

(ii) To the second portion, add NH\(_3\), solution in drops and then in excess.

(iii) To the third portion, add BaCl\(_{2(aq)}\) followed by dilute HCI.

 

(b) Divide the residue into two portions.

(i) Heat the first portion strongly in a test tube.

(ii) Add dilute HCI  to the second portion. 

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Explanation
Tes  Observation Inference 

(a)(i) C + H\(_2\)O, then filter 

 

(ii) Filterate + NaOH\(_{(aq)}\) in drops,

then in excess 

 

(iii) Filterate + NH\(_{3(aq)}\) in drops,

then in excess 

 

(iv) Filterate + BaCl\(_{2(aq)}\) + dil. HCl

 

(b)(i) First portion of residue + heat  

 

(i) Second portion of residue + dil. HCl 

Green residue, blue filterate

 

Blue gelatinous precipitate 

insoluble in excess  

 

Pale blue (gelatinous) precipitate 

ppt dissolves/soluble in excess to give a deep blue solution 

 

White precipitate insoluble in dil. HCl

 

Colour changed from green to black powder 

 

Effervescence, colourless, odourless gas which turned lime water milky 

 

C is a mixture of soluble and insoluble salts 

 

Cu\(^{2+}\) present 

 

Cu\(^{2+}\) confirmed 

 

 

SO\(_4^{2-}\) confirmed 

 

 

 

 

Gas is CO\(_2\) from CO\(_3^2\)

 


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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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Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
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Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 24709
NECO June/July 2024 - Get offline past questions & answers - Download objective & theory, all in one app 48789