Waec 2018 Chemistry Practical Answers – May/June Expo

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Waec 2018 Chemistry Practical Answers – May/June Expo

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(1a)
Volume of pipette used=25.0cm^3
TABULATE
Reading: Rough|1st|2nd|3rd
Final reading: 16.00|15.40|17.20|15.30
Initial reading: 0.00|0.00 |2.00 |0.00
Vol of acid used: 16.00|15.40|15.20|15.30

Average volume of A used = (VA1 + VA2 + VA3) cm³
VA = (15.40 + 15.20 + 15.30)/3cm³
VA = 45.90/3 = 15.30cm³.

B contains 4.80g/250cm³
Hence x8 = 1000cm³
X = 4.80 × 1000/250 = 4.80 × 4 = 19.2gdm³

(1bi)
Hence molar concentration of B in moldm3
Mass Conc(8dm³) = molar Conc × molar mass
Molar Conc of B = mass conc/molar mass = 19.2gdm³/127gmol
Cb = 0.151moldm3

(1bii)
Concentration of A in moldm-³, CA is given by CAVA/CBVB = na/nb
Where CA = ?
VA = 15.30cm³,
na = 1
CB = 1.51moldm-³, VB = 25.0cm³, nb = 5
CA × 15.30/0.151 × 250= 1/5
Therefore CA = 0.151×25×1/15.30×5 = 3.775/76.50 = 0.049moldm-³
Hence Conc. Of A in moldm-³ = 0.049moldm-³

(1biii)
No of moles of Fe²+ in the volume of B pipetted
n= cv/1000 =
0.151×25.0/1000 =
3.775/1000
= 0.003775moles of Fe²+

2a)
-Test = C+NaOH in drop till in excess
-Observation = Blue PPT insoluble in excess
-Inference = Cu2+ is present
2aii)
-Test = C+NH3 in drop till in excess
-observation = Pale blue soluble in excess, aqeous ammonia to
give a deep blue solutions
-Inference = Cu2+ is present
2aiii)
-Test = C+Dil HNO3 + AgNO3 sol
-Observation = White PPT
-Inference = Cl is confirmed
2bi)
-Test = D+NaOH in drop till excess + heat
-Observation = Colourless gas evolved with characteristic choking
smell, turns litimus paper blue
-Inference = Gas is NH3, NH4 is present
2c)
-Test = D+Dil Hcl + Lime
-Observation = Residue dissolves liberating a colourless gas which
turns lime water milky
-Inference = gas is CO2 , CO^2-3 present

SEE ALSO:   NECO GCE 2017 Biology Practical Questions &Answers/Expo/Runs.

 

SUBSCRIBING BEFORE THE EXAM DAY MAKES YOU SAFER BCOS YOU’LL GET PASSWORD EARLIER ON THAT EXAM DAY. ALWAYS SUBSCRIBE A DAY BEFORE EACH EXAM.

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