2017/2018 neco chemistry practical questions and answers

1) Volume of Pipette used 25.0cm^3

Titration | Rough | First | Second | Third 
Final burette reading (cm^3) | 22.50 | 45.10 | 32.65 | 27.60
Intial burette reading (cm^3) | 0.00 | 22.50 | 10.00 | 5.00
Volume of A used (cm^3) | 22.50 | 22.60 | 22.65 | 22.70

1a) Average volume of A = 22.60 + 22.65 + 22.70/3

= 22.65cm^3

1bi) GIVEN: CB = 0.10moldm^-3
VB = 25cm^3
CA = ?
VA = 22.65cm^3

Equation of reaction:
H2C2O4(aq) + 2NaOH(aq) ====> Na2C2O4(aq) + 2H2O(l)
hence, nA = 1
Nb = 2

Using CAVA /CBVB = nA/nB
CA = CBVBnA/VanB
=0.10 * 25 * 1/22.65 * 2

CA = 0.055 moldm^-3

Concentration of A in moldm^-3 = 0.055

bii) Using: 
gram concentration = molar concentration * molar mass
conc. Of A in gdm^-3 = 0.055 * [(1*2) + (12*2) + (16*4)]
= 0.055 * 90
= 4.95gdm^-3

legendary…..
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3i) S02 changes the colour of acidified K2Cr2O7 solution from orage to green when it is passed through it by changing it to Cr2(So4)3 solution

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ii) When Zinc dust is added to CuSo4 solution, the solution turns from blue to white.

iii) Due to the formation of Cr2(So403 solution.

iv) Due to the formation of white ZnSo4 since Zn is higher in the electrochemical series

3b) DRAW THE DIAGRAM BY YOURSELF. ‎
S/N
TEST
OBSERVATIONS
INFERENCE‎
————————————‎
 2ai.
TEST‎
X + 5cm distilled water, divided the solution into 4 portion
OBSERVATION ‎
Effervescence occurs, a reddish brown gas with irritating smell evolved
INFRENCE ‎
NO2 gas from NO3 ‎
_____________________________‎

bi)‎‎
TEST‎‎
1st portion + NaOH in drop
OBSERVATION ‎
White ppt formed
INFRENCE ‎
Pb2+ or Ca2+
______________________________‎
TEST‎
In excess
OBSERVATION ‎
Soluble in excess
INFRENCE ‎
Pb2+ present
_______________________________‎

bii)
TEST‎
2nd portion + NH3 in drops & dilute NH3 solution 
OBSERVATION ‎
White ppt formed
INFRENCE ‎
Pb2+ or Al3+
_________________________________‎

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TEST‎
In excess
OBSERVATION ‎
Ppt insoluble in excess
INFRENCE ‎
Pb2+ 
___________________________________

biii)
TEST‎
3rd portion + dil. HCl in drop
OBSERVATION ‎
White ppt insoluble
INFRENCE ‎
Pb2+ present
_____________________________________‎

Ci)
TEST‎
Y + Conc. HNO3
OBSERVATION ‎
Yellow color is formed
INFRENCE ‎
Protein present
_______________________________________

Cii)
TEST‎
Heat the produce formed in Ci. Above + Conc. NH3
OBSERVATION ‎
Yellow colour remained 
INFRENCE ‎
Protein is confirmed
________________________________________‎
Ciii)
TEST
Add Conc. NH3 to the product in cii
OBSERVATION 
Yellow colour remained 
INFRENCE 
Protein is present 
___________________ ______‎

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