Waec May/June 2013 Chemistry Practical Specimen

This is the Waec May/June 2013 Chemistry Practical Specimen. Candidates should note that this Waec May/June 2013 Chemistry Practical Specimen is just a guide for them to prepare for the exams. ExamsGuru Team is not liable in wrong handling of this information or in any where advice any candidate to indulge in exams malpractice because it is not only spoiling the individual but the society at  large.

REAGENTS for Waec May/June 2013 Chemistry Practical Specimen
Red and Blue Litmus Paper.
Aqueous Ammonia.
Dilute Hydrochloric.
Barium Chloride Solution
Dilute trioxonitrate(V) acid

APPARATUS for Waec May/June 2013 Chemistry Practical Specimen
Glass rod.
Filtration paper.
Spatula.
Two boiling tubes.
Four test tubes.
Methyl Orange indicator.
Wash Bottle containing distilled/deionized water.
Mathematical table/calculator.

Each candidate should be supplied with the following, where ‘n’ is the candidate’s serial number.
(a.) 150cm3 of tetraoxosulphate(VI) solution in a corked flask or bottle, labelled ‘An’.
These should all be the same containing 5.5cm3 of concentrated H2SO4 per dm3 of solution.
(b.) 150cm3 KOH solution, in acorked flask or bottle labelled ‘Bn’.
These should be same containing 5.6g of KOH per dm3 of solution.
(c.) One spatulaful: (NH4)2SO4.FeSO4.6H2O in a specimen bottle labelled ‘Cn’.

Waec May/June 2013 Chemistry Practical Specimen : Summary and Hints for candidates

1. VOLUMENTRIC ANALYSIS

QUESTION 1.
‘A’ is a solution of tetraoxosulphate(vi).
B is a solution coomtaining !.4g of potassiumb hydroxide per 25.0cm3.
(a.) Put A into burette and titrate with 20.0cm3 or 25.0cm3 portion into of B using Methyl Orange as an indicator.
Record the volume of your pipette.
Tabulate your burette readings and calculate the average volume of acid used.
(b.) From your result and information provided. Calculate the
(i.) Concentration of B in mol/dm³
(ii.) Concentration of A in mol/ dm³
(iii.) Number of Hydrogen ions in 1.0dm² of A.

The equation for the reaction is: H₂SO₄ + 2KOH –> k₂SO₄ + 2H₂O.
{H=1, O=16, K=39}

SOLUTION
Burrete reading(cm3)| Rough | 1st  | 2nd  | 3rd
Final(cm3)  | 18.60 | 18.00| 20.30| 28.00
Initial(cm3) | 0.00   | 0.00  | 2.30  | 10.00
Vol. Acid used(cm3)| 18.60 |18.00 | 18.00| 18.00

The average volume of acid used = 18.00 + 18.00 + 18.00/3 = 18.00cm3.

(bi.) Mass of KOH per dm3 of B = 39+16+1= 56.
Conc. of B = 5.6/56 = 0.01mol/ dm³.
(bii.) The equation for the reaction is: H2SO4 + 2KOH –> k2SO4 + 2H2O.
From the equation ==>
Conc of A  X Volume of A  X Mole ratio =
CA X 18.00/0.10  X 2 = ½
.’. CA = 0.10  X 25/2  X 18
CA= 0.0694mol/dm3.

(biii.) 1dm3 of 1.0mol/dm3 H2SO4 contains (2 X 6.0  X 10²³).
Hydrogen atom ==> 1 dm³ of 0.694mol/ dm³
H₂SO₄ contains 2  X 6.0  X  10²³ = 8.328×10²².

QUESTIONS & SOLUTIONS to QUANTITATIVE/SALT ANALYSIS
QUESTION (2a.)
C & D are inorganic salts. X is a solution of an inorganic compound.
Carryout the following exercises on C, D & X.
Record your observations and identify any gas(es) evolved.
State the conclusion drawn from the result of each test.
[i.] Add about 5cm3 of distilled water to sample C in a test tube and shake thoroughly. Divide the esulting solution into two portions.
[ii.] Put about 2cm3 of X into seperate test tubes and add the first portion of solution in (2ai).
[iii.] To the second portion of the resulting solution in (2ai), add few drops of BaCl₂(aq) followed by excess dil HCl.
[bi.] To about 2cm3 portion of the resulting solution in a test-tube, add NaOH in drops and in excess.
[ii.] To another portion of the resulting solution, add few drops of dilute trioxonitrate.

SOLUTION

TEST
[2ai.] C + distilled H₂O.
[ii.] 1st portion + BaCl₂(aq).
[iii.] 1st portion + BaCl2 + HCl.
[iv.] Residue + dil HCl.

[bi.] 2nd portion + NaOH in drops + excess NaOH.
[ii.] C + HNO₃.
[iii.] C + dil HNO₃ + NH₃ in drop and in excess NH₃.

Waec May/June 2013 Chemistry Practical Specimen OBSERVATIONS
[2ai.] Dissolves completely.
[ii.] White ppt is formed.
[iii.] Ppt dissolved.
[iv.] A colourless gas is elvolved and effervescence occured.

[bi]. Dark green ppt.  Ppt insoluble in excess NaOH.
[ii.] Effervescence occured.
[iii.] Insoluble in drop.  Soluble in excess NH3.

INFERENCE
[2ai.] A soluble salt is present.
[ii.] SO₄^2-, SO₃^2-  S^2-, or CO₃^2- suspected.
[iii.] SO₃^2-  – present.
[iv.] H₂ present.

[bi.] Fe²⁺ Confirmed.
Fe³⁺ formed.
[ii.] CO₂^2- – suspected.
[iii.] SO₃^2-  – present.