Exams/School Gist

# FREE NECO 2020 CHEMISTRY PRACTICAL ANSWERS

## NECO 2020 CHEMISTRY PRACTICAL ANSWERS – EXPO RUNS

VERY IMPORTANT INFORMATION FOR NUMBER 1!!!
PLEASE REMEMBER TO USE YOUR’S SCHOOL’S AVERAGE TITRE VALUE(AVERAGE VOLUME OF ACID). WE USED 21.47cm3, TRY TO KNOW YOUR SCHOOL’S AVERAGE TITRE VALUE. ASK YOUR CHEMISTRY TEACHER. THEN, ANYWHERE YOU SEE 21.47cm3 IN MY CALCULATION, PUT YOUR SCHOOL’S OWN AND RE-CALCULATE. THIS IS VERY IMPORTANT!!!

(1)
Volume of pipette is 25.00cm³

Titrations |Rough| 1 | 2 | 3
Final Reading|23.00|21.50|21.40|21.50
Initial Reading|0.00|0.00|0.00|0.00
Vol. Of acid used|23.00|21.50|21.40|21.50

(1a)
Vol of acid used VA = 21.50+21.40+21.50/3
= 21.47cm³

(1bi)
Conc. Of A in g/dm³ = 3.65÷500/1000 = 7.3g/dm³
Conc. of A in mol/dm³ = gram conc/molar mass
= 7.3/[1+35.5] = 7.3/36.5
=0.2mol/dm³

(1bii)
Using CAVA/CBVB = nA/nB
0.2×21.47/CB×25.00 = 2/1
CB = 0.2×21.47/25.00×2
= 0.08588mol/dm³

(1biii)
Molar mass of B = gram conc/molarity = 10.60/0.08588
=123.43g/mol

(1biv)
X2CO3 = 123
2[X] + 12 + 3 = 123
2x + 60 = 123
2x = 123 – 60 = 63
X = 63/2 = 31.5

(1bv)
No of moles of X2CO3 = molarity × volume
= 0.08588 × 25
= 2.147moles

Mole ratio of X2CO3 to CO2 is 1:1
Therefore, No of moles of CO2 released = 2.147moles
Volume of CO2 released = 2.147 × 22.4
=48.1dm³ (2ai)
Tabulate:
TEST: C + 5cm³ of distilled water and shake thoroughly. Divide the solutions into three portions.

OBSERVATION: A pale green solution results

INFERENCE: Salt is soluble

(2aii)
TEST: To the first portion add NaOH solution in drys

OBSERVATION: Dark green gelatinous was formed

INFERENCE: Fe²+ present.

(2aiii)
TEST: then in excess

OBSERVATION: Precipitate is insoluble

INFERENCE: Fe²+ present

(2aiv)
TEST: To the second portion add K3Fe(CN)6 solution

OBSERVATION: A dark blue precipitate formed

INFERENCE: Fe²+ confirmed

(2bi)
TEST: To the third portion add AgNO³ solution

OBSERVATION: White Precipitate formed

INFERENCE: SO4²- , CL-, CO²- present

(2bii)
TEST: To the results obtained in add dilute HNO3 in drops , then excess

OBSERVATION: White Precipitate is insoluble

INFERENCE: CL- present

(2biii)
TEST: To the results obtained in add NH3 solution

OBSERVATION: White Precipitate dissolves

INFERENCE: CL- Confirmed Keep Refreshing!

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