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1995 WAEC Chemistry Practical Credit will be given for strict adherence to instructions, for observations precisely recorded, and for...

Chemistry
WAEC 1995

Credit will be given for strict adherence to 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 simple salts. Carry out the following exercises on C. Record your observations and identify any gases evolved. State the conclusion you draw from the result

(a)(i) Put all C in a boiling tube or beaker and add about 10cm\(^{3}\) of distilled water Stir the mixture thoroughly and tilter Keep both the residue and the filtrate

(ii) Test the filtrate with litmus paper.

 

(b) Divide the filtrate of two portions

(i) To the first portion of the filtrate. add about 2cm\(^3\) of dilute trioxonitrate (v) acid and then silver trioxonitrate (v) solution

(ii) To the second portion of the filtrate, add sodium hydroxide solution in drops until it is in excess.

 

(c) Put half of the residue in a test tube and heat strongly. Allow to cool

 

(d)(i) Put the remaining half of the residue in a test tube and add about 2cm\(^3\) of dilute hydrochloric acid.

(ii) To the resulting solution from (d(i)) above, add aqueous ammonia in drops until it is in excess.

 

 

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Explanation
Test Observation

Inference

(a)(i) C + water filtration  Partly soluble white milky suspension. White residue. colourless filtrate Filtrate is neutral 
(ii) Filtrate + litmus  No effect on litmus  Filtrate is neutral 
(b)(i) Filtrate + dil HNO\(_3\) + AgNO\(_{3(aq)}\)

No visible reaction 

White precipitate 

Cl\(^{-}\) present 
(ii) Filtrate + NaOH\(_{(aq)}\) in drops and in excess 

White precipitate 

precipitate insoluble 

Ca\(^{2+}\) present 
(c) Residue + heat  Residue turns yellow and white when cold ZnO present 
(d)(i) Residue + dil HCl  Effervescence/gas - evolved, odourless gas turns lime water milky 

Gas is CO\(_2\)

CO\(_3^{2-}\)

(ii) Soln. from d(i) + NH\(_{3(aq)}\) in drops until in excess  white ppt. which is soluble gives a colourless soln.  Zn\(^{2+}\) confirmed 

 


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WAEC offline past questions - with all answers and explanations in one app - Download for free
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 24709
Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
WAEC May/June 2024 - Practice for Objective & Theory - From 1988 till date, download app now - 99995
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 24709
WAEC offline past questions - with all answers and explanations in one app - Download for free
WAEC May/June 2024 - Practice for Objective & Theory - From 1988 till date, download app now - 99995
Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts