2021 WAEC GCE 2021nd series Chemistry Practical Answers : 2020 WAEC GCE 2nd series Chemistry Practical Answers Night before Exam

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(1a)
Mass number A = 1.85g
Vol of A = 250cm³
Mass of B =400g in 1dm³

Average title = 25.00+24.90/2

=49.90/2=24.95cm³

(1b)
(i) yellow
(ii) colourless

(1ci)
Conc of B in mol/dm³ ; ?
Mole =4.00/40 =0.1mol

Mole = conc * vol(dm³)
Conc =mole/vol
Conc =0.1/1
Conc=0.1mol/dm³
Conc of B =0.1mol/dm³

(1cii)
Cb=0.1mol/dm³ , Vb=25.0cm³ , Ca =? Va=24.95cm³
na=1, nb=1
CaVa/CbVb
Ca*24.95/0.1*25.0=1/1
Ca=0.1*25.0/24.95=2.5/24.95=0.100mol/dm³

(1di)
Molecular mass=?
Mass conc =1.85/250*1000
=7.4g/dm³
Conc(mol/dm³)=mass conc/molar mass
0.1=7.4/molar mass
Molar mass =7.4/0.1= 75g/mol

(1dii)
A=CnH²n+1COOH
CnH²n+1COOH=74
(12*n)+(1x(2n+1)+12+16+16+1=74
12n+2n+1+45=74
14n+46=74
14n=74-46
14/14=28/14
n=2
C²H⁵COOH

(1e)
This is because it is a reaction between weak acid and strong base

(1a to 1c)


(1 d to 1e)

(2a)
TEST
C(aq) + HCl

OBSERVATION
No gas evolved/No observable reaction

INFERENCE
SO²,⁴^- Some may be Present

(2b)
TEST
C+BaCl² + dili H²SO⁴

OBSERVATION
White Precipitate Formed Precipitate insoluble remain Undissolved

INFERENCE
SO²,⁴^- confirmed

(2ci)
TEST
C+NaOH(aq) In drop them in excess

OBSERVATION
No precipitate / No visibie reaction
No Observation reaction.

INFERENCE
Probably NH+⁴ Present

(2cii)
TEST
mixture in c(i) warmed

OBSERVATION
Gas is evolved
Gas is basic
Gas has a Pungent or smell

INFERENCE
NH₃ gas evowed hence NH³ presert

(2di)
TEST
C+HNO³ + AgNO³

OBSERVATION
No observable reaction
No gas evolved

INFERENCE
C1^- Present

(2dii)
TEST
Precipitate + HNO³

OBSERVATION
White precipitate
Precipitate insolubie

INFERENCE
C1^-confirmed

(2ei)
(i)(NH⁴)²SO⁴
(ii)NH⁴Cl

(2eii)
(i)Ammonium teraoxosulphate(iv) salt(NH⁴)²SO⁴)
(ii)NH⁴CI > Ammonium chloride

(3ai)
There will be evolution of SO²

(3aii)
a green color is observed

(3aiii)
There is effervescence I:e CO² is liberated

(3b)
(i)HCl
(ii)Zn(OH) will dissolves readily while (⁴(OH)² will not.

(3c)
(i)it reduce the mass of the salt
(ii)to purity it