Nabteb 2016 Chemistry Practical Answers

NABTEB CHEMISTRY PRACTICAL ANSWERS
PLEASE NOTE
THIS SIGN:
/ means DIVISION
* means Multiplication
^means Raise to power
================
1a)
volume of pipette Vf=25.00cm^3
1aii)
1)TABLE OF RESULT
Burette Readings (cm^3),
Rough Titration,
First Titration,
second Titration,
Burette Reading |final(cm^3)|Initial(cm^3)|volume of acide(cm^3)|
Rough tire|24.80|0.00|24.80|
1st titre|49.30|24.80|24.50|
2nd titre|24.40|0.00|24.40
Average Volume of Acid Used VE=24.50 24.40/2 VE=24.45cm^3
1bi)
conc. of f(moldm^3) =mass conc/molar mass
molar mass NaOH =23 16 1=40glmol
conc of F=3.90/40
=0.098moldm^3
1bii)
using Ce Ve/Cf Vf =Ne/Nf
Ce*24.45/0.098*25=1/2
conc of E =0.098*25/24.45*2=0.050moldm^3
1biii)
conc of E in gldm^3=2.45*100/500=4.90gdm^3
1bvi)
molar mass of H2X=mass conc/molar conc
=4.90/0.050 =98gmol^1
================
2a)
TABULATE
under TEST
2ai)sample G H20 filtration
2aii)filtrate litmus paper
2bi)1st portion filtrate AgNO3 dil.HNO3
2bii)mixture in (2bi) NH3(aq)
2biii)2nd portion filtrate NaOH(aq) heat
2c)residue dil.HCl heat
2di)solution from (2c) drops NaOH and in excess
2dii)solution from (2c) NH3(aq)
under OBSERVATION
2ai)sample G solube partially to give a colourless filtrate
2aii)turns red litmus paper to blue
2bi)white ppt is formed
2bii)the precipitate dissolve in excess NH3(aq)
2biii)a colourless gas with irritating smell which form a white
dense fume with conc HCl stopper
2c)dissolve with effervescerence of colourless,odourless,acid gas
which turn lime water milky
2di)white gelatinous ppt soluble in excess NaOH(aq)
2dii)white gelatinous ppt is formed which dissolve in excess NH
3(aq)
under INFERENCE
2ai)sample G is a mixture of soluble and insoluble salts
2aii)basic solution
2bi)Cl^- present
2bii)Cl^- confirmed
2biii)NH3 from NH^ 4 present
2c)CO^-2 gas from CO3^2 or HCO^-3
2di)Pb^2 Zn^2 or Al^3 present
2dii)Zn^2 confirmed
=======================
3a)
i)copper trioxocarbonate(vi) CuCO3
ii)carbondioxide(CO2) gas
iii)copper (Cu)
3b)
CuCO3(s) heat—-> CuO(s) CO2(g)
3c)
TEST=drops of sodium hydroxide plus the solution
OBSERVATION=blue gelatinous precipitate which is not dissolve
in excess sodium hydroxide
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