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Practical – Chemistry 2015 Neco Answers Available Now!!!




Thursday 4th June Paper I: Practical –
Chemistry
10.00am-12.00pm
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Volume of burette | Rough | Ist titre |
2nd titre
Final Reading(cm) | 26.00 | 22.40 |
32.24
Initial Reading(cm)| 0.00 | 0.00 | 0.00
Volume of A. (cm) |26.00 | 22.40 | 22.40
Average volume used= ( 22.40 +
22.40 )/2
=22.40cm3
(I) Conc, of A in mol/dm3= mass/molar
mass
Mass of A is 3.89g/dm3
Molar mass of A(Hcl) = ( 1 + 35.5 ) =36.5
Therefore 38.9/36.5
=0.1066mol/dm3
(ii) Conc. Of B in mol/dm3= CaVa/CbVb =
Na/Nb
= 0.1066 x 22.40/Cb x 25.00 = 1/1
Cb = 1 x 0.1066 x 22.40/25.00 x 1
Cb = 0.0955mol/dm3
Conc. Of B in g/dm3= molar conc of
B x molar mass of B
= 0.0955 x 40
= 3.82g/dm3
(Iii) Conc. Of B in g/dm3= molar conc of
B x molar mass of B
= 0.0955 x 40
= 3.82g/dm3
1c) It is often used in titrations because
of its
clear and distinct colour change.
Because it
changes colour at the pH of a mid-
strength
acid, it is usually used in titrations for
acids.
Unlike a universal indicator, methyl
orange
does not have a full spectrum of colour
change, but has a sharper end point.

(2i)TEST: Add 5cm3 of distilled water 2
all of X in a beaker. Stir & filter. Keep both
d filtrate & residue.
OBSERVATION: Salt x dissolve partially in
water
INFERENCE: salt x is a misture of soluble
and insolube salt
——————————————————
(2ii)TEST: Divide d filtrate into two
portions. (i) To d first portion add a few
drops of dilute HNO3 followed by
aqueous solution of AgNO3
OBSERVATION: white precipitate is
formed
INFERENCE: Cl may present
——————————————————
(2iii)TEST: Add NH3OH in excess to d
resulting mixture in B(i).
OBSERVATION: The white ppt dissolved
in excess NH4OH(aq)
INFERENCE: Cl^- is present
——————————————————
(2iv)TEST: To d second[Receiving Text]
portion add
ammonia solution in drops.
OBSERVATION: White ppt is formed
which soluble in excess
INFERENCE: Zn^2+ is present
——————————————————
(2v)TEST: To d second[Receiving Text]
portion add
ammonia solution in excess
OBSERVATION: White ppt is not soluble
INFERENCE: PB^2+ or Al^3+ are likely to
present
——————————————————
(2vi)TEST: Dissolve the Residue in above
5cm3 of dilute HNO3, divide the resulting
soluble into two portion
OBSERVATION: Effervescence occur and a
gas that turns lime water milky is
evolved
INFERENCE: Co2 gas is involved from
Co3^2-
——————————————————
(2vii)TEST: To d second portion add
aqueous solution of potassium-iodide.
OBSERVATION: Yellow ppt is formed
INFERENCE: PB2+ is present
——————————————————
(2viii)TEST: Heat & allow to cool
OBSERVATION: The ppt desolve and re-
appear on cooling
INFERENCE: Pb2+ is confirmed

3ai. Inorganic Chemistry/Qualitative
Analysis/Tests for anions

3aii. for the starch iodine test is
performed in
which the starch reacts with iodine to
produce dark blue colour which
confirms
the presence of starch.
for glucose benedict’s and fehling’s test
is performed.
benedict’s test:

3b. Calcium chloride

3c. Burette
Conical flask
Pipette
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