Neco 2017/2018 Chemistry Practical Free Expo Answers

Neco 2017 Chemistry Pratical Free Expo Answers 2ai ) Tabulate - Test - Xn +10cm 3of H 2O and stirred - Observation - Xn dissol...

Neco 2017 Chemistry Pratical Free Expo Answers

2ai )

Tabulate
- Test -
Xn +10cm 3of H 2O and stirred
- Observation -
Xn dissolves to form a colourless solution
- Inference -
Xn is a soluble salt

2aii )
- Test -
First portion of Xn + NaOH ( aq ) in drops ,then
in excess
- Observation -
White precipitate which dissolves in excess to give a colourless solution
- Inference -
Zn2 +,Pb 2+, orAl3 + present

2aii )
- Test -
Second portion of Xn +NH3( aq ) in drops ,
then in excess
- Observation -
White precipitate in soluble in excess
- Inference -
Pb 2+orAl 3+ present

2aiii )
- Test -
Third portion of Xn +dil. HCl
- Observation -
White crystalline / chalky precipitate
- Inference -
Pb 2+confirmed

2bi )
- Test -
Yn + litmus
- Observation -
Red litmus paper turned blue
- Inference -
Yn is alkaline

2bii)
- Test -
Portion of Yn+ conc . HNO 3
- Observation -
Yellow colouration
- Inferrence -
Protein present


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


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

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









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