2012 Neco Exams Practical Chemistry

CHEMISTRY PRACTICALS.[/u]
VOLUMETRIC ANALYSIS:
1. All your burette readings(initial and finals) as well as the size of your pipette must be recorded but NO account of experimental procedure is required.
A is a Solution containing 1.04g HCl per 500cm3 of solution.
B is prepared by diluting 50.0cm3 of saturated solution of Na2CO3 at room temperature to 100cm3
(a.) Put A into the burette and titrate it against 20.cm3 or 25.0cm3 portions of B using Methyl Orange as an indicator.
Repeat the titration to obtain consistent titres.
B.) Tabulate your result and calculate the
(i) Concentration of A in mol/dm3
(ii) Concentration of B in Mol/dm3
(iii) Solubility of Na2CO3 in mol/dm3
(iv) Volume of CO2 that would be liberated from 1dm3 of B if the titration were carried out at S.T.P.

SOLUTIONS:
The Equation for the Reaction: Na2CO3 + 2HCl = 2NaCl + H2O + CO2.

TABLE OF VALUE:
Bur Rd|Rough|1st|2nd |3rd
Final|25.00|24.90|34.90|24.90
Initial|0.00|0.00 |10.00 |0.00
Vol. |25.00|24.90|24.90|24.90

NOTE: Rough,1st titre,2nd titre,3rd titre are all in (cm3)
AVERAGE VOLUME OF ACID USED
= 24.90+24.90+24.90/3
= 74.7/3
=24.90cm3.

(Bi) Conc. of A in g/dm3
= 1.04*1000/500
= 2.08g/dm3
Molar mass of HCl
= 1*35.5 = 36.5g/dm3
.:. Conc. of A in mol/dm3
= 2.08/36.5 = 0.057mol/dm3.

(ii) CaVa/CbVb = Na/Nb
= 0.057*24.90/Cb*25 = 2/1
Cb = 0.057*24.90/25*2
= 1.4193/50
= 0.02839
= 0.0284mol/dm3.

(iii) To calculate the Solubility of Na2CO3 in Mol/dm3.
The dilution factor of B = 50 to 1000 mole of Na2CO3 liberate 22.4dm3 of CO2 at S.T.P.

(iv).:. 0.0284mole of Na2CO3 will liberate 22.4*0.0284
=0.64dm3 of CO2.
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SALT ANALYSIS:
2. (a) TEST:
Put all of C in a boiling tube and cee about 5cm3 of distilled water. Divide the resulting solution into two portions.

OBSERVATION:
White residue partially dissolved.

INFERENCE:

(i) *TEST:
To the first portion, add about 2cm3 of BaCl2 solution.

*OBSERVATION:
White ppt.

*INFERENCE: SO4^2-,CO3^2-, SO3^2- Suspected.

TEST:
The dilute HCl in excess
OBSERVATION:
INFERENCE: Cl^- Present.
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(ii) TEST:
To the second portion of the solution, add two drops of phenolphthalein indicator.

*OBSERVATION:
Pink colouration observed.

*INFERENCE:
CO3^2-,SO3^2- Suspected.
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(b) TEST:
Dissolve all of D in a boiling tube with about 5cm3 of distilled water. Divide the resulting solution into two equal parts.

*OBSERVATION:
Partially soluble in water.

*INFERENCE: Ca^2+, Pb^2+, Zn^2+ Suspected.

(i) TEST:
To the first portion, add ammonia solution.

*OBSERVATION:
White gelatineous ppt

*INFERENCE:
Cl^- present.
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(ii) TEST:
To the second portion, add NaOH solution in Drop.

*OBSERVATION:
White ppt formed.

*INFERENCE:
Ca^2+ present.

TEST:
Then in excess.
OBSERVATION:
Insoluble in excess.
INFERENCE:
Ca^2+ present.
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(NOTE THAT THE ABOVE SOLUTION WILL BE IN A TABULAR FOR i.e
TEST|INFERENCE|OBSERVATION)

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QUESTION NO 3. DO IT URSELF