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NECO 2016/2017 Chemistry Practical Specimen Answers – June/July

NECO 2016/2017 Chemistry Practical Specimen Answers – June/July

Tuesday 31st may 2016
CHEMISTRY PRACTICAL 10:00am-12:00pm
+++++++++++++++++++++++++++++++++++
1)
volume of pipette used =25.0cm^3

indicator used =methyl orange

burette reading|rough| 21.50|0.00|21.50|

final burette readings (cm^3)|1st|21.20| 0.00. 21.20|

initial burette reading(cm^3)|2nd|31.20|10.00| 21.20|

volume of a used (cm^3)|3rd|41.20|20.00|21.20|

average volume of a used =(21.20+21.20+21.20)cm^3/3
=63.60cm^3/3
=21.20cm^3

equation of the reaction
H2SO4(aq) + 2NaoH(aq)+2H2O(s)
nA=1,nB=2
A=4.90gldm^3 H2SO4
molar mass H2SO4
=(1*2)+32+(16*4)
=2+32+64
=98gmol^-1

molar conc A=mass con A/molar mass A
=4.90gldm^3/98glmol
=0.05moldm^3

CAVA/CBVB=nA/nB
0.05moldm^3*21.20cm^3/CB*25.0cm^3=1/2
0.05moldm^3*21.20*2=CB*25.0
CB=0.05molldm^3*21.20*2/25.0
CB=0.0848moldm^3
in mass conc B =Molar B*MolarBmass
B=NaoH
=23+16+1
=40gmol-^3

mass conc B =0.0848moldm^3 * 40gmol

mass con B = 3.392gldm^3
% mass of impusx 100%/total mass of implusty

mass of implus =(4.0-3.392)gldm^3
=0.608gldm^3

%impurity =0.608gldm^3*100%/4.0gldm^3
=15.2%

(2ai)
Observation: The salt sample dissolves completely
Inference: C is a mixture of soluble salts

(2aii)
Observation: White precipitate insoluble in excess NaOH(aq)
Inference: Ca^2+ present

(2aiii)
Observation: No visible reaction
Inference: Ca^2+ is present

(2aiv)
Observation: Brownish fume is produced
Inference: NO2(g) form, NO3^- present

(2av)
Observation: Formation of brown gas which forms a ring junction with FeSO4
Inference: NO2 form, NO3^- confirmed

(2bi)
Observation: D dissolves completely. Formation of dirty green precipitate insoluble in excess NaOH(aq)
Inference: D is soluble in salt, Fe^2+ present

(2bii)
Observation: Formation of a white precipitate.precipitate remains insoluble in HCl(aq)
Inference: SO3^2-,CO3^2-,SO4^2- present,SO4^2- confirmed

(3ai)
Diagram

(3aii)
using CAVA=CBVB
=>2 moldm^-3=0.20moldm^-3
VB=2*40 /0.2
=400cm^3
the volume of distilled water required is 400cm^3

(3bi)
Ethanol<Ethanoid acid<Trioxo nitrate (V) acid
===========>increasing order of acidity

(3bii)
To achieve end points quickly and easily

+++++++++++++++++++++++++
(A) ONE BURETTE (50cm³)
(B) ONE PIPETTE (20cm³) OR
25cm³)
NOTE:ALL CANDIDATES IN A
CENTRE MUST USE PIPETTES OF
THE SAME VOLUME.
(C) THE USUAL OF THE SAME FOR
FILTRATION
(D) THE USUAL APPARATUS AND
REAGENTS FOR QUALITATIVE
WORK INCLUDING:
(i) RED AND BLUE LITMUS PAPER
(ii) AQUEOUS AMMONIA
(iii) DILUTE HNO³-
(iv) DILUTE SILVER
TRIOXONITRATE (V)
SOLUTION
(v) AQUEOUS SODIUM
HYDROXIDE
(vi) DILUTE HCI
(vii) POTASSIUM THIOCYNATE
SOLUTION
(viii) POTASSIUM
HEPTAOXOCHROMATE
(VII)
SOLUTION
(ix) BARIUM CHLORIDE
SOLUTION
(E) SPATULA
(F) FILTRATION APPARATUS
(G) ONE BEAKER
(H) ONE BOILING TUBE
(I) FOUR TEST TUBE
(J) PHENOLPHTHALEIN
INDICATOR
(K) METHYL ORANGE INDICATOR
(I) MATHEMATICAL TABLE/
CALCULATOR
(M) WASH BOTTLE CONTAINING
DISTILLED/ DEIONIZER WATER
++++++++++++++++++++++++

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Posted by on May 30, 2016.

Categories: Uncategorized

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