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Thursday, 13th July, 2024
Chemistry (Practical): 10:00 am – 012:00 noon
Real NECO Chemistry Practical Questions Below:
NECO CHEMISTRY PRACTICAL SOLUTIONS
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(1a)
[TABULATE]
Burette Reading (cm³) | Rough | Titration I | Titration II
> Final Reading (cm³) | 21.50 | 43.00 | 22.00
> Initial Reading (cm³) | 0.00 | 21.50 | 00.00
> Volume of A used (cm³) | 21.50 | 21.50 | 22.00
(1ai)
Solution B[Sodium trioxocarbonate (iv)] feels soapy
(1bi)
Conc. B in mol/dm³ =?
Ca= 0.04, Va= 21.50cm³, na= 1
Cb= ? , Vb= 25.00cm³ nb= 1
CaVa/CbVb = na/nb = 0.04×21.50/Cb×25.00 = 1/1
Cb= 0.04×21.50/25.00 = 0.86/25.00
Cb= 0.0344mol/dm³
(1bii)
Conc. of B in g/dm³ = Conc. of B in mol/dm³ × molar mass of B
Molar mass of B(NaCO₃)= (23×2) + 12 + (16×3) = 106
:. Conc. of B in g/dm³ = 0.0344×106 = 3.6g/dm³
(1biii)
1 mole of Na₂Co₃ = 1mole of Na₂So₄
:. 0.0344 mole of Na₂Co₃ = 0.0344 mole of Na₂So₄
№ of mole= mass/ molar mass
Molar mass of Na₂So₄= (23×2)+32+(16×4)=142
:. 0.0344 = mass/142
Mass=142×0.0344=4.9g
(1biv)
1 mole of Na₂Co₃= 1 mole of CO₂
0.0344 mole of Na₂Co₃ = 0.0344 mole of CO₂
:. № of mole = volume/ molar volume = 0.0344 =
volume of CO₂/22400cm³ =771cm³
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(2ai)
[TABULATE]
=TEST=
C + heat
=OBSERVATION=
Formation of yellow flame
=INFERENCE=
Na⁺ present
(2aii)
=TEST=
C + distilled water + shake
=OBSERVATION=
It readily dissolve in water
=INFERENCE=
C is a soluble in water
(2aiii)
=TEST=
Solution C + litmus paper
=OBSERVATION=
It changes moist red litmus to blue and no effect blue
=INFERENCE=
Solution C is alkaline
(2bi)
=TEST=
1st portion of solution C + barium chloride
=OBSERVATION=
White precipitate formed
=INFERENCE=
CO₃²⁻ , SO₄²⁻ , S²⁻ or SO₃²⁻
(2bii)
=TEST=
Add dilute HCl to product in (bi)
=OBSERVATION=
White precipitate dissolved
=INFERENCE=
CO₃ , SO₃²⁻ or S₃²⁻
(2biii)
=TEST=
To the second portion add phenolphthalein
=OBSERVATION=
Purple colour observed
=INFERENCE=
C is alkaline
(3ai)
phenolphthalein
(3aii) I. Pink ll. Colourless
(3aiii)
(i)To give a sharp change in colour at the end of the acid base reaction
(3aiv)
(i)the burette must be rinsed with the acid or allow it to drain after rinsing with distilled water
(ii)Air bubble must not be allowed in the burette
(3av)
Neutralization reaction
(3bi)
I. Hofmann voltameter.
II. Kipp‘s apparatus
(3bii)
Because silver nitrate is photosensitive (i.e.sensitive to light) Therefore,if the silver nitrate is left in sunlight or any bright light, it breaks down (hydrolyses) to give black/brown silver oxide and nitric acid.
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