2013 chemistry practical,question and answers

CHEMISTRY PRACTICALS 2013
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 inmol/
dm3
(iii.) Number of Hydrogenions in
1.0dm^2 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
* Volume of A* Mole ratio =
CA*18.00/0.10*2 = 1/2.'. CA=
0.10 * 25/2*18' CA= 0.0694mol/
dm3.
(biii.) 1dm3 of 1.0mol/
dm3H2SO4
contains (2*6.0*10^23).
Hydrogen atom ==> 1dm3 of
0.694mol/ dm3
H2SO4 contains 2*6.0*10^23 =
8.328x10^22.
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NOTE: THIS IS JUST A STUDY OF
THE
SPECIMEN THAT WAEC PROVIDED.
THESE ARE LIKELY QUESTION U
WILL SEE ON PRACTICAL DAY.
TRY TO USE THE END POINT( ie Ur
school's Volume of acid used) OF
UR SCHOOL( IT MATTERS A LOT);
AS OURS IS 18.00AS SHOWN
ABOVE..
***SUBSRIBERS SHOULD NOT
WORRY COS THEY WILL GET THE
EXACT ANSWERS ON THE EXAM DAY
AS THEY PAID FOR..
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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 ofeach test.
[i.] Add about 5cm3 of distilled
water to sample C in a test tube
and shake thoroughly. Dividethe
esulting solution intotwo
portions.
[ii.] Put about 2cm3 of X into
seperate test tubesand add the
first portionof solution in (2ai).
[iii.] To the second portion of the
resulting solution in (2ai), add
fewdrops 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.
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.] Fe^2+ Confirmed.
Fe^3+ formed.
[ii.] CO2- suspected.
[iii.] SO3^2- present.
NOTE THAT ^ Means Raise to
Power and above is a questi0n
likely to show up during the
exam. Use it and refresh ur
memory....