2024 NECO GCE CHEMISTRY OBJ AND ESSAY ANSWER

CHEM-OBJ
1-10: ACDBABDEBB
11-20: ADCCCCBEBA
21-30: DDDCCCDCAB
31-40: CBCCDEBBAC
41-50: EABDDBABDC
51-60: EBABCDEDEB
==================================

(4a)
(i) This is the point at which the indicator changes colour in a volumetric titration
(ii) Volume of Acid VA = 25cm^3
Concentration of Hcl CA = 0.4moldm^3
Volume of NaoH VB = 20vm^3 , na = 1 , nb = 1

(4d)
(i) A flame is a visible, gaseous part of a fire
(ii) The source of the fire producing the flame
– the temperature of the flame
(iii) Because oxygen supports combustion and combustion of oxidation is involved in almost all activities in the universe
(iv) Zn(s) + 2Hcl(aq) —-> Zncl2(aq) + H2(g)
===============

(4a)
(i) This is the point at which the indicator changes colour in a volumetric titration
(ii) Volume of Acid VA = 25cm^3
Concentration of Hcl CA = 0.4moldm^3
Volume of NaoH VB = 20vm^3 , na = 1 , nb = 1

Using the relation = CAVA/CBVB = na/nb

0.4*25/CB*20 = 1
CB = 0.4*28/20 = 10/20 = 0.500
Concentration of NaoH CB = 0.500moldm^3

(iii)
– Methyl orange
– Phenolphthalein

(4bi)
– A compound can only be separated through chemical reactions while mixture can through physical methods
– The individual components of a compound do not retain their individual properties but the constituents of a mixture still retain their individual properties

(4bii)
– NaoH
– Na2CO3.10H2O

(4ci)
– Acids react with bases to form salt and water only as the product
– Acids ionize in water to form hydrogen ions as the only positive ion.
– *Acids liberate hydrogen gas when reacted with m3tals

(4cii) This is because of the dissolution of Nitrogen oxide NO and sulphur (iv) oxide in water

(4d)
(i) A flame is a visible, gaseous part of a fire
(ii) The source of the fire producing the flame
– the temperature of the flame
(iii) Because oxygen supports combustion and combustion of oxidation is involved in almost all activities in the universe
(iv) Zn(s) + 2Hcl(aq) —-> Zncl2(aq) + H2(g)
=====================================

(6ai)
Ethane does not react with ammonia silver nitrate while Ethyne gives a yellow white precipitate when bubbled through ammonial silver nitrate solution.
C2H2 + 2AgNO3 –> Ag2C2 + 2HNO3
Ethene gives no reaction.

(6aii)
C₂H₄ + H₂ –> C2H₆

H H
| |
C = C + H₂
| | Hydrogen
H H
Ethene
H H
| |
–> H- C-C -H
| |
H H
Ethane

(6bi)
It is not safe for a human to stay in closed garage because the exhaust fumes produced by incomplete combination of petrol would be consumed by the person and which is poisoned. The exhaust gas is CO2. Two third if this gas in one’s volume of blood causes death.

(6bii)
Relative atomic mass of an element is the ratio of an average mass per atom of an element from a given sample to 1/2 mass of a carbon-12 atom

(6biii)
2SO₃ + O₂ —> 2SO₄
2 moles of SO₃ replied 1 mole of O₂
0.25mole of SO₃ gives 0.125moles of O₂.

No of mole = volume given/molar volume
Nmole = volume / 22.4
= 5.6/22.4
0.25mole of SO₃

No of mole of O2 = volume /22.4
0.125 = volume/22.4
Volume = 2.8dm³ or 2800cm³

(6ci)
The importance of NaCl in sopa production is to separate the soap from glycol formed and to aid the solubility of the soap formed

(6cii)
(i) It is most effective in removing scom ie they clean effectively.
(ii) They are non-biodegradable and they harm the environment.

(6di)
(i) They are affected by PH
(ii) They are produced from a source and they have their effect on the target organs.
(iii) They are Proteinous in nature.

(6dii)
Heat disrupts hydrogen bonds and non Polar hydrophobic interactions and also Protein globules tend to uncoil when heated.

(6diii)
Denaturation
=====================================

(3ai)
(i) Physical change
(ii) Chemical change.
(iii) Physical change.

(3aii)
The periodic law states that atomic mass of element is s periodic function of their chemical properties.

(3aiii)
(i) Elements within the same group have the same chemical properties.
(ii) Elements change gradually from metal to non-metals across the period.
(iii) The arrangement of elements in a horizontal form is called period while the vertical arrangement is called group

(3aiv)
(i) Calciumchloridehypochloridte CaCl(OCl)
(ii) Calcium hypochlorite Ca(OCl)₂
(iii) Calcium chloride CaCl₂

(3bi)
Avogadro’s law states that equal volumes of gases at the same temperature and pressure contain equal number of molecules.

(3bii)
0.25mole of Argon = 15cm³
Mass of one mole of Argon = 40g
40g = 1 mole
Xg = 0.25 = 10g
Hence 10g of Argon = 15cm³
10g of Neon = 10/20 = 1/2 = 0.5mol will contain 2 × 15cm³ = 30cm³ of gas

(3ci)
Fermentation is the breakdown of substance by bacteria, yeasts or microorganisms typically involving effervescence and the evolution of heat.

(3cii)
H H
\ /
C=C + H₂O
/ \
H H

H H
| |
<=> C-C-OH
| |
H H

<=> C₂H₄ + H₂O <=> C₂H₅
=====================================

(2ai)
Photosynthesis

(2aii)
Sources of chemical
– Industrial effluent
– Laboratory effluent

(2aiii)
Unpaired electrons present in the D-orbital of Fe^2+ S-electrons

(2bi)
– Pig iron
– Cast iron
– Wrought iron

(2bii)
– Susceptibility to individual exposure to toxic chemicals
– Irritation of some body parts when toxic gases are inhaled

(2ci)
A – Sulphur
B – Magnesium
C – Oxygen
D – Chlorine

(2cii)
The type of bond between B and D is ionic bond

(2ciii)
Electronic configuration of C using Spdf notation
Oxygen = 1s22s22p4

(2civ)
– Their hardness increases with increasing ionic charge
– They have high melting and boiling points

(2di)

(2dii)
– The valency of mercury is +2
– The valency of lead in PbO2 is +4
===============

Posted by admin on 24th November 2019.

Tags: 2021 NECO GCE CHEMISTRY OBJ AND ESSAY ANSWER

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