2025 NECO CHEMISTRY: 2025 NECO CHEMISTRY PRACTICAL ANSWERS (7398)

(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 'copied from e x p o c o d e . n e t free' 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

(1)

(2a)
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

(2)

(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.

(3)