Neco Chemistry Practical Expo 2017/18 (Questions & Answers) Runs.

Neco Physics Practical Expo
Neco Physics Practical Expo

NECO CHEMISTRY PRACTICAL EXPO 2017.

Neco Physics Practical Expo
Neco Chemistry Practical Expo

CHEMISTRY PRACTICALS NECO 2017.

1. A is a solution containing 6.30gdm-3 of impure
ethanedioic acid. B is 0.100moldm-3 sodium
hydroxide solution. Put A into the burette and titrate
it against 20.0cm3 or 25.0cm3 portions of B using
phenolphthalein as indicator. Repeat the titration
three more times and record your results in the
table below;
Volume of pipette = 25.0cm3

TITRATION
ROUGH(cm3)
1ST(cm3)
2ND(cm3)
3RD(cm3)

FINAL BURETTE READING
21.20
30.60
25.70
22.80
INITIAL BURETTE READING
0.00
10.00
5.00
2.00
VOLUME OF ACID USED
21.20
20.60
20.70
20.80
Calculate the average volume of A = (1st + 2nd +
3rd)/3
= (20.60+20.70+20.80)/3
= 62.10/3 = 20.70cm3
From your results and information provided above,
calculate
Concentration of A in moldm-3
Eqn : H2C2O4 + 2NaOH —— Na2C2O4 + 2H2O
Mole ratio of A : B = 1 : 2.
Using (CaVa/CbVb) = (Na/Nb)
(Ca*20.70/0.100) = ½
Ca = (0.100*25)/(20.70*2)= 2.50/41.40= 0.0603864
Ca = 0.0604moldm-3
Concentration of solution A in gdm-3
Molar Mass of A{H2C2O4} = (1*2) + (12*2) +(16*4)
= 2 + 24 +64
= 90g/mol
Conc of A in gdm-3 = Conc of A in moldm-3 * Molar
mass
=0.0604*90
= 5.44 gdm-3
Percentage purity of A
% purity of A = (Conc of pure/ Conc of Impure)*100
= (5.44/6.30)*100
= 86.35%
Hence, % impurity = 100 – 86.35
% impurity = 13.65%
Volume of solution A that would neutralize a solution
containing 0.005 mole of NaOH
25cm3 of 0.100 moldm-3 NaOH contain
(25/1000)*0.100 = 0.0025 mole
If 20.70cm3 of A neutralizes 0.0025 mole of NaOH,
0.005 mole of NaOH will be X
=(20.70*0.005)/0.0025 = 41.4cm3
C i. What would be the color of methyl orange
indicator in soln. B?
Ans: Yellow or Orange
ii. Give the reason why methyl orange is not
suitable for this
Ans: Ethanedioic acid is a weak acid while sodium
hydroxide is a strong
base. Methyl orange is not suitable because the
endpoint will not
coincide with the pH of indicator.
S/N
TEST
OBSERVATIONS
INFERENCE

2ai.

X + Heat
Effervescence occurs, a reddish brown gas with
irritating smell evolved
NO2 gas from NO3

3ai)
i) SO2 change the colour of acidified K2Cr2O7 solution from
Orange to green when it is passed through it by changing to
Cr2(SO4)3
solution
ii) when zinc dust is added to CuSO4 solution, the solution turn
from Blue to white
3aii)
i)Due to the formation of Cr2(SO4)3 solution
ii)Due to the formation of white ZnSO4 since zinc is higher in
electrochemical series
3b)
DRAW and label a diagram for a set up that can be used to
separate suspension of chalk dust in water
(check above images for the drawing)
[6/12, 9:14 AM] Jizzy: No2 solution
2a)
*TEST*
X + 5cm of distilled water, Divide the solution into 4 portion
*OBSERVATION*
Salt X is soluble in distilled water
*INFERENCE*
Salt X is soluble salt
=======================
2bi)
*Test*
-To the first portion, Add dilute NaOH in drop
-then in excess
*OBSERVATION*
-White precipitate solution is formed
-The white precipitate is soluble
*INFERENCE*
Zn^2+ Pb^2+ and AL^3+ are present
=====================
2bii)
*TEST*
-To the 2nd portion add dilute NH3 solution in drop
-then in excess
*OBSERVATION*
White gelatinous precipitate is formed which is insoluble in
excesa
*INFERENCE*
Zn^2+,Pb^2+ and Al^3+ are present
======================
2biii)
*TEST*
To the 3rd portion, Add dilute HCL in drops
-then in excesa
-heat the solution
*OBSERVATION*
White precipitate is formed which Dissolved on heating and re-
appears on cooling
*INFERENCE*
Pb^2+ confirmed
======================
2ci)
*TEST*
Sample Y + concentrated HNO3
(Cii)
Heat the product formed in (ci)
*OBSERVATION*
Dirty white curd is formed
===========
It turn to yellow colouration on heating
*INFERENCE*
Protein is present
====================
2ciii)
*TEST*
Add concentrated NH3 to the product in (cii)
*OBSERVATION*
The product in (Cii) turns to orange colour
*INFERENCE*
Protein is present.

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