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CHEMISTRY PRACTICAL NECO 2014 FREE EXPO ANSWERS. here









(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
======================

(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


(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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Posted By KellyChi On 03:36 Tue, 03 Jun 2014

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