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👑 2019 WAEC GCE CHEMISTRY PRACTICAL ANSWERS👑
100% VERIFIED CHEMISTRY PRACTICAL THEORY ANSWERS
H2SO4(aq) + 2NaOH(aq) —-> Na2SO4(aq) + 2H2O(l)
Volume of Acid Va = 21.60cm³
Volume of Alkali Vb = 25.0cm³
Mass of NaoH
2.0g = 500cm³
Xg = 1000cm³
X = 1000×2.0/500
X = 2×2 = 4.0g/dm³
Then mass conc = molar conc × molar mass
.:. molar conc of B = mass conc/molar mass
Where the molar mass of NaOH
=23+16+1 = 40gmol^-1
.:. Conc of NaOH in moldm^-³ = 4.0g/dm³/40g/mol
CaVa/CbVb = na/nb
Ca×21.60/0.1×25 = 1/2
Ca = 0.1×25/2×21.6
CA = 0.058mol/dm^-³
Concentration of H2SO4 in mol/dm^-³ = 0.058mol/dm-³
Recall that mass conc of H2SO4
= Molar conc × Molar mass
Where molar mass of H2SO4
= 2 + 32 + 64
Mass conc of H2SO4 = 0.058× 98
(i) I would ensure the air bubble present is removed before taking the initial reading.
(ii) I would ensure I keep my eye in level with the liquid surface while taking the burrette reading.
(iii) I would ensure there is no leakage from the burette during titration.
INFERENCE: NO3- suspected, Gas is acidic.
OBSERVATION: Color changes from yellow to red
(2bi & 2bii)
INFERENCE: NO3- confirmed
OBSERVATION: White ppt, solube in excess
INFERENCE: PB2+, Al3+, Ca2+ suspected
OBSERVATION: Precipitate dissolves and reappears on cooling
INFERENCE: Pb2+ present
OBSERVATION: A white ppt of AgCl. Dissolves in NH3
INFERENCE: Cl- suspected
(i) Boiling tube
(ii) Evaporating dish
Fill a container with warm water and pour the mixture NaCl and activated charcoal. Stir properly to dissolve it. The activated charcoal will float instantly and it is filtered off using a filter paper, the dissolved salt(filtrate) is then heated till the H2O is evaporated leaving the NaCl as residue.
(i) It can be use for teeth whitening and health.
(ii) It can be use for skin care.
(i) NaCl is Not decomposed by heat
(ii) Na2CO3.10H2O effloresces, losing all or most of its water of crystallization
The acid used in this titration is dilute sulphuric acid. Nitric acid is not used as it is itself an oxidising agent and hydrochloric acid is usually avoided because it reacts with KMnO4 according to the equation given below to produce chlorine and chlorine which is also an oxidising agent in the aqueous solution.
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