Waec 2017 Chemistry Practical Answers – May/June Expo
Tuesday, 11th April, 2017
Chemistry 3 (Practical Alternative A) 09.30am – 11.30am
ATTENTION:- NOTE THAT SUBSCRIBERS GETS ANSWERS BEFORE THE EXAM STARTS..
ALWAYS SUBSCRIBE IF YOU NEED FAst and early runz
Burette reading|Final burette reading(cm^3)|Initial burette reading (cm^3)|Volume of acid used(cm^3)|
First- 25.02, 0.00, 25.05
Second- 25..03, 0.00, 25.03
Third- 25.03, 0.00, 25.03
Average volume of A used = 25.02 + 25.03+ 25.03cm^3/3
Frm the equation, mole ratio of acid to base is 2:1
Using CAVA/CBVB = nA/nB
0.2*25.03/CB*25 = 2/1
C contains 14.3g in 500cm3
.:. Conc of c in gdm^-3 is 28.6dm^-3.
Conc in dm^-3 = conc in mol/dm3 * molar mass
Molar mass = 28.6gdm^-3/0.100moldm^3
The hydrated salt is NA2CO3.XHO=286
The number of water molecules in the hydrated salt is 10
TEST: F + water
OBSERVATION: Partially soluble salt
Inference: F is a mixture of soluble and insoluble salts
TEST: Filtrate + NaOH(aq)in drops,then in excess
OBSERVATION: A pale blue gelatinous precipitate which is insoluble in excess NaOH(aq).
INFERENCE: Cu2+ present
TEST: Filtrate + NH3(aq) in drops,then in excess.
OBSERVATION: A pale blue precipitate was formed. The precipitate is soluble in excess NH3(aq)to give a deep blue solution.
INFERENCE: Cu2+ confirmed
TEST: Filtrate + dilute HNO3(aq) + AgNO3(aq)
OBSERVATION: White precipitate formed which turns grey on exposure to light.
INFERENCE: Cl- present
TEST: Residue + HNO3(aq)
OBSERVATION: Effervescence of a colourless, odourless gas which turns moist blue litmus paper faint and turns lime water milky.
INFERENCE: CO2(g) from CO3^2- or HCO3- present
TEST: Residue + NaOH(aq)
OBSERVATION: White powdry ppt insoluble in NaOH(aq)
INFERENCE: Ca2+ present.
The colour of methyl orange will change from orange to yellow
Iron(III)chloride will be reduced from brown iron to green iron
The color of KM2O4 is decolorized because SO2(g) acts as a reducing agent.
Addition of ethanoic acid to KCO3 results to the liberation of a colorless and odorless gas CO2 which turns lime water milky
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