NECO 2017 Chemistry Practical Answers – May/June Expo

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?NECO 2017 CHEMISTRY PRACTICAL ANSWERS?

100% VERIFIED CHEMISTRY PRACTICAL ANSWERS

Note:​ Candidates are strongly advised to check which size of pipette used by their school.

We make used of 25cm³ in the solution

——————————-

If your school used 20cm³, all you need do is use it in place of 25cm³ anywhere we used it and calculate accordingly

​NOTE:ALWAYS MAKE USE OF YOUR SCHOOL ENDS POINT

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

CLICK HERE TO VIEW THE TABLE

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
======================

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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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 CUSO 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) CLICK HERE TO VIEW THE DIAGRAM

====COMPLETED====

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