Get 2018/2019 Nabteb Chemistry Practical A Day To Exam Here

(1a)
Volume of Pipette = 25.0cm
TABULATE
Burette reading |rough |1st |2nd|3rd|
Final burette reading (cm³) |24.90| 39.50|34.80|24.50
Initial Burette reading (cm³) |0.00|15.00|10.00|0.­00
Volume of E used (cm³) |24.90|24.50|24.80|2­4.50

Average volume of acid used
= (24.50+24.80+24.50)cm/3
= 24.50cm³
= 24.50cm³

(1bi)
Concentration of E (CE) in moldm
= mole x 1000/volume
4.90g ==> 500cm³
xg ==> 1000cm³
x = 4.90x1000gdm³/500
=9.80gdm³

Molar mass (H2S04) = 1×2 + 32 + 16×4
= 2+ 32 + 64
= 98gmol
Concentration (mole dm³) = 9.80gdm³/98
= 0.100moldm³

(1bii) CEVE/CFVF = Ne/Nf
= 0.100×24.50/Cf x 25.0 =1/1
Cf = 0.100×24.50/25×1
Cf = 2.45/25 moldm³
= 0.0980moldm³

(1biii) Concentration of F in g/dm
Conc (gdm³) = molar mass x conc
Molar mass (Na3CO3) = 23×2 + 12 + 16 x3
=106gmol³
Conc (gdm³) = 106gmol x 0.0980
=10.39gdm³

=============================================

(2)
TABULATE:
Test | Observation| Inference

(2a)
TEST:
G + 8cm³ of distilled water

OBSERVATION:
Sample G dissolves partially in water colourless

INFERENCE:
G is a mixture of soluble and insoluble salt

(2bi)
TEST:
1st portion + HNO3(aq) + AgNO3(aq)

OBSERVATION:
A white precipitate is formed

INFERENCE:
Cl- present

(2bii)
TEST:
2nd portion + NaOH + heat

OBSERVATION:
A purgent irritating, choking gas is liberated which turns moist red litmus paper blue

INFERENCE:
Gas is NH3 from NH4+

(2c)
TEST:
Residue + H2SO4(aq)

OBSERVATION:
Residue dissolve completely on warming

INFERENCE:
Residue is soluble in acid

(2ci)
TEST:
1st portion + NaOH(aq) in drops than excess

OBSERVATION:
A pale blue precipitate is formed which is insoluble in excess

INFERENCE:
Cu2+ present

(2cii)
TEST:
2nd portion + NH3(aq) in drops, then excess

OBSERVATION:
A pale blue precipitate is formed which dissolved in excess to give deep blue solution

INFERENCE:
Cu2+ present

===============================================

(3a)
Effervescence of brownish gas which turns a moist litmus paper red and a black precipitate or residue of lead sulphide is formed.
Pb (NO3)(aq) + H2S(g) ==> Pbs(s)black + H2O(i) + NO(g)

(3bi)
-H2SO4 ==> strong acid
-CH3COOH ==> weak acid

(3bii)
H2SO4 is strong because it ionises completely in water while CH3COOH is weak acid because it ionise partially in water

(3c)
Heat the mixture, ammonium chloride sublime and it then condenses to solid NH4Cl