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Neco 2016 Chemistry practical question and Answers – june/July Expo

Neco 2016 Chemistry practical question and Answers – june/July Expo

VERIFIED NECO 2016 CHEMISTRY PRACTICAL QUESTIONS AND ANSWERS

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

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Posted by on May 30, 2016.

Categories: Uncategorized

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3 Responses

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