NECO 2021 CHEMISTRY PRACTICAL ANSWERS

 CHEMISTRY-PRACTICAL

No. 1

 *(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=0.106*23*50*1/25.00*1

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

=0.1*40

=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=0.0025*1=0.0025mol of NaSO⁴

Molar mass of Na²SO⁴=(23*2) + 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

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 *(2a)* 

TEST

C + 5cm³ of distilled water

OBSERVATION

It dissolve completely

INTERFERENCE

C is a soluble salt

 *(2bi)* 

NO. 2

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

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 *(3a)* 

No. 3

(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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Completed!

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