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2019/2020 Neco past Chemistry Practical Questions and Answers |


2019 Neco SSCE JUNE/JULY Chemistry Practical free solution


(Q1).
The volume or pipette used 25.00cm³
In a tabular form
Titrations |rough |1st|2nd|3rd|
Final reading |21.00|41.30|20.40|40.90
Initial reading|0.00|21.00|0.00|20.40
Vol of A used |21.00|20.30|20.40|20.50
(1ai)
Average volume of A = 20.30+20.40+20.50/3
=61.2/3
=20.40cm³

(1aii)
H2X(aq) + 2NaOH(aq)–>Na2X(aq) + 2H2O(l)

(1bi)
Mass conc. of B = 1g/250cm³
= 1g/0.25dm³ = 4g/dm³
Using :
Molar conc. = mass conc./molar mass
= 4/(23+16+1) = 4/40 = 0.1mol/dm³

(1bii)
Using CAVA/CBVB = nA/nB
CA = CBVBnA/VAnB
CA = 0.1×25×1/20.4×2
Concentration of A = 0.06127mol/dm³


(1biii)
Molar mass of A = mass conc/molar conc
=4.85/0.6127
=79.15
≅ 79gmol
(1c)
(i)it might contain traces of impurities which must be removed before being weighed

(ii)it is hygroscopic which readily absorb moisture from atmosphere


(Q2).

FILL IN THE TABLE:
(2i)
OBSERVATION:
Solution turns blue
INFERENCE:
Copper salt suspected.
(2ii)
OBSERVATION:
Blue gelatinous precipitate
Insoluble in excess NaOH
INFERENCE:
Cu²+ suspected
Cu²+ Confirmed
(2iii)
OBSERVATION:
Blue gelatinous precipitate
Soluble in excess NH³
INFERENCE:
Cu2²+ Suspected
Cu²+ Confirmed
(2iv)
OBSERVATION:
White precipitate
INFERENCE:
SO4²- Suspected
(2v)
OBSERVATION:
Precipitate insoluble in excess
INFERENCE:
SO4²- confirmed




(Q3).

(3ai)
Methyl orange
(3aii)
I. Yellow
II. Orange
(3aiii)
(i)To give a sharp change in colour at the end of the acid base reaction
(3aiv)
(i) The burette must be rinsed with the acid or allow it to drain after rinsing with distilled water
(ii)Air bubble must not be allowed in the burette
(3av)
Neutralization reaction
(3bi)
I. Hofmann voltameter.
II. Kipp’s apparatus
(3bii)
Because silver nitrate is photosensitive (i.e.sensitive to light) Therefore,if the silver nitrate is left in sunlight or any bright light, it breaks down (hydrolyses) to give black/brown silver oxide and nitric acid.

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