100% CHEMISTRY PRACTICAL NECO 2014/2015 QUESTION AND ANSWER PAGE

NECO CHEMISTRY PRACTICAL

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(1)
Tabulate:
Titration|Rough|1|2|3|
Final burette reading(cm3)|22.50|22.40|22.40|22.40
initial burette reading(cm3)|0.00|0.00|0.00|0.00
volume of acid used(cm3)|22.50|22.40|22.40|22.40
(a)calculate the average volume of A used=22.4+22.4+22.4/3
=22.40cm3

(1bi)concentration of A in moldm-3
mass concentration=3.89g/dm3
molarmass=36.5g/mol
molar concentration=mass concentration/molar mass
=3.89/36.5 moldm-3
=0.107moldm-3


(1bii)
CaVa/CbVb=Na/Nb=1/1
=0.0973*22.4/Cb*25.0=1/1
Cb=0.0973*22.4/25
Cb=0.00389*22.4
=0.087136moldm-3
(1biii)molar concentration of B=40g/mol
molar concentration=0.00389moldm-3
mass concentration=molar concentration * molar mass
=0.00389 * 22.4 *40
=3.48544g/dm3

(1c)
-To indicate the end point
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(2)
Test:
A: Add 5cm3 of distilled water to all X in a beaker.stir and filter,keep both the filtrate and residue
B: Divide the filtrate into two portions
(i): To the first portion add few drops of dilute HNO3 followed by aqueous solution of AgNO3
(ii): Add NH4OH in excess to the resulting mixture on B(i)
(iii): To the second portion add aqueous ammonia in drops.then in excess

C: Dissolve the residue in about 5cm3 of dilute HNO3.Divide the resulting solution into two portions
(i):To the first portion add ammonia solution in drops
(ii):Then in excess
(iii):To the second portion add aqueous solution of potassium iodide
(iv):Heat and allow to cool

OBSERVATION:
A: Partially soluble colourless filtrate white residue
B:
(i)white precipitate
(ii)precipitate dissolved
(iii)white gelatinous precipitate.precipitate dissolved

C:Effervescence of odourless gas which turn lime water milky
(i):white precipitate
(ii):precipitate dissolved
(iii)yellow precipitate
(iv)dissolved on warming and reappear on cooling

INFERENCE:
A: X contains soluble and insoluble salts

B:
(i) Cl- present
(ii) Cl- confirmed
(iii)Zn2+,Al3+,Pb2+ present
Zn2+ confirmed
C: colourless gas is CO2 from CO3^2-
(i):Pb2+,Al3+ or Zn2+ present
(ii):Pb2+,Al3+ present
(iii):Pb2+ present
(iv)Pb2+ confirmed
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(3a)
(i)H2S turns lead(II) acetate paper black while SO2 does not
(ii)Glucose-Fehlings test
-Add about 1cm3 of fehling's reagent to about 2cm3 of the solution.Boil the mixture
OBSERVATION: A brownish red precipitate is observed showing the presence of glucose

Starch-Iodide test
To an aqueous solution of the substance add a few drops of iodide solution
OBSERVATION: solution turns blue-black
INFERENCE: starch is present

(3b)
-calcium chloride(CaCl2)
-Calcium oxide(CaO)
(3c)-Conical flask
-Burette
-Pipette
-Indicator
-Acid
-Base










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