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CHEMISTRY PRACTICAL NECO 2016 Free Expo Answers From Wapbaze


NECO MAY/JULY 2016 TIMETABLE

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Tuesday 31st may 2016
CHEMISTRY PRACTICAL 10:00am-12:00pm
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(1)
TABULATE
Burette reading(cm^3):Final reading(cm^3),Initial reading(cm^3),Volume of acid used(cm^3)
Rough:26.00,2.00,24.00
1st reading:25.50,1.00,24.50
2nd reading:24.50,0.00,24.50
3rd reading:24.50,0.00,24.50
Average volume of acid used
=1st+2nd+3rd/3
=24.50+24.50+24.50/3
=24.50cm^3

Concentration of A mol/dm^3=Conc g/dm^3/molar mass
Molar mass of H2SO4 =2(1)+32+4(16)
=98g/dm^3

Concentration mol/dm^3=4.90/98
=0.05mol/dm^3

(i)
Using CaVa/CbVb=na/nb
(0.05*24.50)/Cb*25)=1/2
Cb=(0.05*24.50*2)/25
=0.098mol/dm^3

(ii)Concentration of B in g/dm^3=Conc in mol/dm^3*molar mass
Molar mass of NaOH=26+16+1=40g/mol
=0.098mol/dm^3*40g/mol
=3.92g/dm^3

(iii)percentage purity of B=Concentration of pure/concentration of impure *100%
=3.92/4*100%
=98%
Therefore percentage of impurity of B =100-98%
=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)





-lid
-sticky tape(to hold paper)
-choroatographic paper
-gas jar
-applied spot of solute mixture
-ion
3aii)
principle of dillution, C1 V1=C2 V2
2.0molldm^3*40
3bi)
ethanol---->ethanoic (acid)---->trioxonotrate
(v) (acid)
3bii)
indicators are used to determine the end point
of the reaction and to test the acidity or
alkalinity of a solution




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