Waec 2016 Chemistry Practical (ALT. A) Answers – May/June Expo

(1)
TABULATE:
Volume of pipette
Burette reading(cm3)|Rough titre(cm3)|1st titre(cm3)|2nd titre(cm3)
Final reading(cm3) |20.00|19.60|19.60
Initial reading(cm3)|0.00 |0.00 |0.00
Volume of acid used |20.00|19.60|19.60
Average titre=(19.60+19.60)/2 cm3
=39.20/2 cm3
=19.60cm3
Equation=>2MnO4^-+5C2O4^2-+16H^+->2NA^2++8H2O+10CO2
(1bi)
Conc of B in mol/dm3
CaVa/CbVb=Na/Nb
(0.05*19.6)/(Cb*25.0)=5/2
5*Cb*25=2*0.05*19.6
Cb=(2*0.05*19.6)/(5*25)=1.96
Cb=0.0157mol/dm3
Cb=0.016mol/dm3
(1bii)
Conc in B in g/dm3
=0.0157*158
=2.4806g/dm3
=2.481g/dm3
==========
2)
TABULATE.
| TEST |
2a) C + water + Filtrated
2b) solution C + AgNO3 + HNO3(aq) is excess
2ci) residuce + HNO3(aq)
2cii)solution of 2ci + NaOH in drops and in excess
2ciii) solution in drop and than in excess
| OBSERVATION |
2a) part of sample C dissolves in meter with colourless filterate salt.
2b) no visible reaction A white precipitate is formed.the precipitate is soluble in excess NH3(aq)
2ci) efferrescence/gas involvd on less gas
2cii) white gelatinous precipitate formed.precipitate is soluble in excess NaOH
2ciii)white gelatinous precipitate is formed.precipitate is soluble in excess NH3(aq)
| INFERENCE |
2a) C is a mixture of solube salt
2b)Cl^- is present Cl^- is confirmed
2ci)Gas is CO2 CO3
2cii) Zn2+ AL3+ or Pb2+
2ciii) Zn2+ confirmed
============
3a)
I) They are used to seperate mixture of colour
II) With colour different boiling point
3bi) To make accurate result of solution
3bii) To avoid error of decimal
3c)
C1 = 2.5mol/dm3
V2 = 500cm
C2 = 0.2mol/dm3
V1 = ?
C1V1 = C2V2
V1 = C2V2/C1
V1 = 0.2 x 500 / 2.5
V1 = 40.0cm3
=============
CL!CK THE L!NK/!MAGE BELOW FOR THE SOLVED ANSWERS
KEEP REFRESHING

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