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2010 WAEC Chemistry Practical Credit will be given for strict adherence to the instructions, for observations precisely recorded, and...

Chemistry
WAEC 2010

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 and D are inorganic salts. X is a solution of an inorganic compound. Carry out the following exercises on C, D and X. Record your observations and identity any gas(es) involved. State the conclusion drawn from the result or each test.

(a)(i) Add about 5 cm\(_3\) of distilled water to C in a test tube and shake thoroughly, Divide the resulting solution into two portions.

(ii) Put about 2cm\(^3\) of X into a separate test tube and add the first portion of solution in (a)(i) To the second portion of the resulting solution in (a)(i), add few drops of BaCl\(_{2(aq)}\) followed by excess dil. HCI.

(b) Add about 10 cm of distilled water to D in a boiling tube and shake thoroughly.

(i) To about 2 cm\(^3\) portion of the resulting solution in a test tube, add NaOH\(_{(aq)}\) in drops and then in excess

(ii) To another 2 cm\(^3\) portion of the resulting solution add few drops of K\(_2\)CrO\(_{4(aq)}\)

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Explanation
  Test Observation Inference
(a)(i) C\(_{(s)}\) C dissolved to give a colourless solution   
(ii)

C\(_{(aq)}\) + X\(_{(aq)}\)

X decolourized/turned colourless  C is a reducing agent 
(iii) C\(_{(aq)}\) + BaCl\(_{2(aq)}\) White precipitate  SO\(_4^{2-}\), SO\(_3^{2-}\) or S\(^{2-}\) or SO\(_3^{2-}\)
  + excess HCl\(_{(aq)}\) precipitate dissolved/precipitate soluble  SO\(^{2-}_3\) confirmed 
(b)  D\(_{(s)}\) + distilled water  D dissolved to give a colourless solution   
(i) 

D\(_{(aq)}\) 

NaOH\(_{(aq)}\) in drops 

+ excess NaOH 

White precipitate 

precipitate dissolved/precipitate 

Pb\(^{2+}\) or Ca\(^{2+}\) 

Pb\(^{2+}\)

(ii) 

D\(_{(aq)}\) + K\(_2\)CrO\(_{(aq)}\) Yellow precipitate  Pb\(^{2+}\) confirmed 

 


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