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NECO Chemistry Practical EXPO Questions & Answers [14th July, 2021]

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Wednesday 14th July, 2021

Paper I: Practical – Chemistry
10:00am – 12:00pm

2021 NECO Physics Practical Questions & Answers [14th July, 2021]

(1a)
Tabulate
Volume of pipette used=25cm3.
Indicator used= Methyl orange
Under Titration, Rough, 1st, 2nd, 3rd,
Final burette reading; |25.00| |23.40| |23.50| 23.60|
Initial burette reading; |0.00| |0.00| |0.00| |0.00|
Volume of A used; |25.00| |23.40| |23.50| |23.60|
(1ai)
Average volume of Acid used=23.40+23.50+23.60/3 =70.5/3=23.50cm3
(1aii)
This is because it is a reaction between a weak acid and strong base

(1aiii)

A funnel should be used while transferring the acid into the burette.

(1bi)

Conc of A in mol|dm³ =?

Conc of A in g|dm³ = 12.75g|dm³

Molar mass of A, NaHSO⁴ = 23+1+32+64

=120g|dm³

 

From.

Conc(mol/dm³) = conc(g/dm³)/molar mass

 

Conc =12.75/120

Conc =0.106mol/dm³

 

(1bii)

Con of B in mol/dm³ =?

Ca =0.106, Cb =? Va =23.50cm³, Vb =25.00cm³

 

na=1 , nb=1

From; CaVa/CbVb=na/nb

Cb=CaVanb/Vbna

Cb=0.10623501/25.001

Cb=2.5/25

Cb=0.1mol/dm³

 

(1biii)

Conc of B in g/dm³=?

Molar mass of B , NaOH=23+16+1=40g/mol

From; conc(g/dm³)=conc(mol/dm³)molar mass

=0.140

=4.0g/dm³

 

(1biv)

Mass of salt formed =?

Recall mole of NaHSO⁴=?

From; mole =con(mol/dm³)*vol(cm³)/1000

 

Mole=0.106*23.50/1000

Mole=0.0025mol of NaHSO⁴

 

By proportion 1mol of NaHSO⁴ produce 1mol of Na²SO⁴ 0.0025mol of NaHSO⁴ will produce X mol of Na²SO⁴ X=0.00251=0.0025mol of NaSO⁴

Molar mass of Na²SO⁴=(232) + 32 + (16*4)

=46+32+64

=142g/mol

 

Recall; mole =mole/molar mass

Mass =mole * molar mass

Mass =0.0025*142

Mass =0.36g of Na²SO⁴


(2a)

[PLEASE PUT IN A TABULAR FORM]

TEST

C + 5cm³ of distilled water

OBSERVATION

It dissolve completely

INTERFERENCE

C is a soluble salt

(2bi)

TEST

Solution + NaOH + Heat

OBSERVATION

Effervescence occurs in which a colourless gas with pungent smell and turns red litmus paper to blue is given off.

INFERENCES

NH³ gas from NH⁴+ is present

(2bii)

TEST

Stirring rod of HCL + gas given off

 

OBSERVATION

a gas which gives a pop sound is given off

 

INFERENCES

H² is present

 

(2ci)

TEST

Solution C + drops of BaCL²

 

OBSERVATION

a white precipitate is formed

 

INFERENCES

CO²^-3, SO²^-4, SO²^-3, May be present.

 

(2cii)

TEST

Solution in C(i) + dil HCL

 

OBSERVATION

the white precipitate dissolve is dil HCL and effervescence occurs in which a colourless and odourless gas which turns blue litmus red and lime water milky is given off

 

INTERFERENCE

CO² gas from CO²^3- confirmed

 

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

 

(3a)

(i)Ca²+

(ii)Pb²+

 

(3bi)

concentrated acid can be defined as an acid formed when a large quantity of an acid dissolve in a small or little volume of water.

 

(3bii)

A strong acid is defined as a type of acid that ionize completely in a solution


(3c)

Activated charcoal is used as an adsorbent material

 

(3d)

(i)Reddish – Brown

(ii) I – red, II – brown.

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