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CHEMISTRY OBJ
01-10: CEDADDCCEC
11-20: ECBAEBAEBD
21-30: BCBDEABCAE
31-40: CDDCBBCDED
41-50: DAEAADDAED
51-60: DBCEECDDEE
COMPLETED
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INSTRUCTION: ANSWER FOUR(4) QUESTIONS ONLY
(1ai)
Fermentation is the slow decomposition by micro-organism of large organic molecules into smaller molecules.
(1aii)
Ethanol Production:
2(C₆H₁₀O₅)n(s) + nH₂O(l) —> nC₁₂H₂₂O₆(aq)
C₁₂H₂₂O₁₁(aq) + H₂O(l) —> 2C₆H₁₂O₆(aq)
C₆H₁₂O₆(aq) —> 2C₂H₅OH(aq) + 2CO₂(g)
(1b)
[FILL IN THE TABLE]
=UNDER FLOURINE=
State at room temperature: Gas
=UNDER FLOURINE=
State at room temperature: Gas
(1ci)
MgCO₃:
Mg = 24, C = 12, O = 16
Molar mass of MgCO₃ = 24 + 12 + (3 × 16) = 24 + 12 + 48 = 84 g/mol
Number of moles= Mass/Molar mass
Number of moles = 25/84 = 0.2976 mol
(1cii)
Methyl orange
(1ciii)
I. Acidic oxide: Sulfur dioxide (SO₂)
II. Neutral oxide: Carbon monoxide (CO)
(1civ)
Hydrophobic compounds repel water and do not dissolve in it, while hydrophilic compounds attract and dissolve readily in water.
(1cv)
I. CH₃CH₂COOH: Propanoic acid
II. CH₃CH₂CH₂CH₂OH: Butan-1-ol
(1di)
The rate of a chemical reaction is the change in concentration of a reactant or product per unit time.
(1dii)
(i) Concentration of reactants
(ii) Temperature
(iii) Surface area of reactants
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(2ai)
An acid anhydride is a compound formed by the removal of water (H₂O) from two molecules of an acid. It reacts with water to form an acid.
(2ai)
(i) Ethanoic acid (acetic acid), CH₃COOH
(ii) Carbonic acid, H₂CO₃
(2aiii)
Fats are solid at room temperature, while oils are liquid at room temperature
(2b)
IMAGE
(2ci)
The periodic law states that the properties of elements are a periodic function of their atomic numbers.
(2cii)
[TABULATE PLEASE]
=Beryllium=
Atomic Number: 4
Electronic Configuration: 1s² 2s²
Valence Electrons: 2
=Aluminium=
Atomic Number: 13
Electronic Configuration: 1s² 2s² 2p⁶ 3s² 3p¹
Valence Electrons: 3
=Potassium=
Atomic Number: 19
Electronic Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹
Valence Electrons: 1
(2ciii)
I. Highest Electronegativity: ₁₇D
II. Same Group: ₃A and ₁₁B
(2civ)
Charcoal
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(3ai)
Entropy is a thermodynamic quantity that measures the degree of disorder or randomness in a system. It can also be described as the measure of how much the energy of atoms and molecules is spread out or dispersed in a process.
(3aii)
Given:
Volume of O₂ = 0.28dm³ = 280cm³
Mass of O₂ = 0.4g
Mass of 1000 cm³ (1 dm³) of H₂ = 0.090g
Molar mass of hydrogen = 2g/mol
Vapour density = (mass of certain volume of gas)/ (mass of same volume of hydrogen) ×(1/2)
Mass of 280cm³ of H₂ = (0.090/1000) × 280 cm³ = 0.0252g
Vapour density = 0.4/0.0252 = 15.87
(3bi)
I. Decrease in temperature
II. Because the forward reaction is exothermic, lowering temperature favours the production of NO₂ to release heat (Le Chatelier’s Principle).
(3bii)
I. Tetraoxosulphate (VI) acid (H₂SO₄):
-Used in the manufacture of fertilizers
-Used as electrolyte in car batteries
II. Diamond:
-Used in cutting tools (glass cutting, drilling)
-Used in jewelry
III. Carbon (IV) oxide (CO₂):
-Used in carbonated drinks
-Used in fire extinguishers
(3biii)
(i) Sodium chloride (NaCl)
(ii) Potassium nitrate (KNO₃)
(3ci)
(i) It is a colourless liquid
(ii) It has a characteristic aromatic (sweet) smell
(3cii)
3,4-dimethylpentan-2-ol
(3ciii)
(i) Keeping chemicals away from heat and sunlight.
(ii) Storing chemicals in airtight containers
(3civ)
Graphite
(3di)
Basicity of ethanoic acid is 1
(3dii)
(i) Strong electrolyte: Sodium chloride (NaCl)
(ii) Weak electrolyte: Ethanoic acid (CH₃COOH) (CH₃COOH)
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(4ai)
Reforming is a process in chemistry where the structure of hydrocarbon molecules is changed to make better fuels, especially petrol. It usually involves breaking and rearranging molecules to improve fuel quality.
(4aii)
Catalytic reforming.
(4aiii)
(i) Cracking produces more petrol (gasoline) from crude oil.
(ii) It provides raw materials for making chemicals like alkenes.
(4bi)
I. Sodium: Yellow
II. Calcium: Brick red
(4bii)
Ca=40
Mass = Number of moles × Molar mass
Mass = 0.50 × 40 = 20g
(4biii)
Molar mass of nitrogen gas (N₂) = 28 g/mol
Number of moles = Mass / Molar mass = 14 / 28 = 0.5 moles
(4ci)
I. Charles’ law: Pressure is constant.
II. Graham’s law of diffusion: Temperature and pressure are constant.
(4cii)
I. Chalk dust in water: Filtration
II. Petroleum: Fractional distillation
(4ciii)
The oil refinery industry uses fractional distillation.
(4civ)
I. Fuel for jet engines: Kerosene
II. Fuel for heavy duty machines: Diesel
III. Coating agent in pipes: Bitumen
(4di)
Quicklime is used as the drying agent.
(4dii)
The formula is XY₂.
(4diii)
(i) Thermoplastics
(ii) Thermosetting plastics
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(5ai)
(i) It is a colourless gas.
(ii) It has a sweet smell.
(5aii)
(i) They form coloured compounds.
(ii) They have variable oxidation states.
(iii) They act as catalysts.
(5aiii)
(i) Filtration
(ii) Chlorination
(5bi)
Given: Q = 9650 C, I = 0.5 A
I. Mass of Copper Deposited:
Number of moles of electrons = Q / F = 9650 C / 96500 C/mol = 0.1 mol
Mass of Cu deposited = (0.1× 63.5)/2 = 3.2g
II. Time Taken:
t = Q / I = 9650 C / 0.5 A = 19300s
(5bii)
Electrolytic refining.
(5biii)
(i) Limestone (CaCO₃)
(ii) Silica (SiO₂)
(5biv)
Used as a building material for making concrete.
(5ci)
Protein denatures (loses its natural structure).
(5cii)
(i) Amino group (-NH₂)
(ii) Carboxyl group (-COOH)
(5ciii)
I. Gas X is Hydrogen (H₂)
II. Gas liberated: Water vapor or steam (H₂O) when H₂ reacts with Fe₂O₃.
III. Physical property of H₂: Colorless and highly flammable gas
(5ciiv)
Let oxidation number of Mn be x.
x + 2(-2) = 0
x – 4 = 0
x = +4
The oxidation number of Mn in MnO₂ is +4.
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(6ai)
An isotope is one of two or more types of atoms of the same element that have the same number of protons but different numbers of neutrons in their nuclei, so they have different atomic masses but similar chemical properties.
(6aii)
I. Given isotopes: ³³₁₅Z and ³¹₁₅Z in a 1:3 ratio
Relative atomic mass = ((33 × 1) + (31 × 3)) / (1 + 3)
= (33 + 93) / 4
= 126 / 4
= 31.5
II. The relative atomic mass is not a whole number because it is a weighted average of the masses of the isotopes, which have different mass numbers and occur in different abundances in nature.
(6bi)
Because they have strong electrostatic forces of attraction between oppositely charged ions that require a lot of energy to break.
(6bii)
(i) Ammonia (NH₃)
(ii) Water (H₂O)
(6biii)
(i) They are soluble in water.
(ii) They have high melting and boiling points.
(6ci)
4Fe(s) + 3O₂(l) + 6H₂O(l) —> 4Fe(OH)₃(s)
(6cii)
(i) Sulfur
(ii) Phosphorus
(6ciii)
Luminous flame is bright and yellow due to incomplete combustion while Non-luminous flame is blue and less bright due to complete combustion.
(6di)
I. A black precipitate of lead (II) sulfide (PbS) forms.
II. The orange solution turns green due to reduction of chromium (VI) to chromium (III).
(6dii)
It has a foul smell .
(6ei)
CO₂(g) + 2NaOH(aq) —> Na₂CO₃(aq) + H₂O(l)
(6eii)
(i) Pollution of water bodies.
(ii) Air pollution causing respiratory problems.
(iii) Soil contamination affecting plant growth.
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