2022 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
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
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
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
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
(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
OBSERVATION:
Solution turns blue
INFERENCE:
Copper salt suspected.
Copper salt suspected.
(2ii)
OBSERVATION:
Blue gelatinous precipitate
OBSERVATION:
Blue gelatinous precipitate
Insoluble in excess NaOH
INFERENCE:
Cu²+ suspected
Cu²+ suspected
Cu²+ Confirmed
(2iii)
OBSERVATION:
Blue gelatinous precipitate
OBSERVATION:
Blue gelatinous precipitate
Soluble in excess NH³
INFERENCE:
Cu2²+ Suspected
Cu2²+ Suspected
Cu²+ Confirmed
(2iv)
OBSERVATION:
White precipitate
OBSERVATION:
White precipitate
INFERENCE:
SO4²- Suspected
SO4²- Suspected
(2v)
OBSERVATION:
Precipitate insoluble in excess
OBSERVATION:
Precipitate insoluble in excess
INFERENCE:
SO4²- confirmed
SO4²- confirmed