2024 NABTEB GCE Chemistry Obj & Essays Answers

NABTEB GCE CHEMISTRY THEORY AND OBJECTIVE ANSWER

CHEMISTRY-OBJ
01-10: ADDBDCCBBC
11-20: DCADBCCBCD
21-30: ABDCBCABDC
31-40: CBCDACBCCB
41-50: BBAACADDCB

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CHEMISTRY ESSAY-ANSWERS

ANSWER FOUR(4) QUESTIONS ONLY
(1ai)
(i) Covalent bonds (between nitrogen and hydrogen).
(ii) Coordinate bonds (between nitrogen and the hydrogen ion).

(1aii)
(i) High melting and boiling points.
(ii) Solubility in polar solvents.
(iii) Good electrical conductivity in the molten or aqueous state.

(1aiii)
(i) Chemical reaction involves the rearrangement of electrons, while nuclear reaction involves changes in the nucleus.
(ii) Chemical reactions do not change the identity of the elements involved, whereas nuclear reactions can result in the formation of new elements.

(1bi)
X (atomic number 9): 1s² 2s² 2p⁵

(1bii)
It belongs to Group 2 of the periodic table (alkaline earth metals).

(1biii)
X is fluorine (F) and Y is magnesium (Mg). Formula: MgF₂

(1biv)
X (Fluorine) is a good oxidizing agent because it has a high electronegativity and a strong tendency to gain an electron to achieve a stable octet configuration. By gaining an electron, it oxidizes other substances.

(1ci)
¹⁴₆C —> ⁰₋₁β + ¹⁴₇N
Y is a beta particle (β)

(1cii)
¹⁴₇N + ⁴₂He —> ¹₁H + ¹⁷₈O
Z is an alpha particle (α)
=======================

(2ai)
(i) Principal quantum number (n)
(ii) Azimuthal quantum number (I)
(iii) Magnetic quantum number (m)
(iv) Spin quantum number (s)

(2aii)
The Pauli Exclusion Principle is violated, as the electrons in the same orbital (2P) cannot have the same spin.

(2aiii)
The Pauli Exclusion Principle states that no two electrons in an atom can have the same set of four quantum numbers. In 2s³, three electrons occupy the same orbital, violating this principle.

(2bi)
(i) Electronegativity decreases.
(ii) Atomic radius increases.
(iii) Reactivity decreases.
(iv) Boiling and melting points increase.

(2bii)
Chlorine (Cl₂)

(2ci)
Covalent bonding is a type of chemical bonding where two or more atoms share one or more pairs of electrons to form a stable molecule.

(2cii)
(Draw the diagram)

(3ai)
The law states that a chemical compound always contains the same proportion of elements by mass, regardless of its source or method of preparation.

(3aii)
To verify the law, I would obtain samples of aluminium oxide from different sources or prepare them through different methods. Then, I would analyze the composition of each sample by measuring the mass of aluminium and oxygen present. If the law holds true, the mass percentage of aluminium and oxygen should be consistent across all samples, within the limits of experimental error.

(3bi)
Boyle’s Law states that, at constant temperature, the volume of a given mass of an ideal gas is inversely proportional to its pressure.

(3bii)
Using Combined gas law:
P₁V₁/T₁ = P₂V₂/T₂

Given values:
P₁ = 80 mmHg
V₁ = 50 cm³
T₁ = 20°C + 273 = 293 K
P₂ = 100 mmHg
T₂ = 3 × 293 K = 879 K
V₂ = ?

V₂ = (P₁V₁T₂)/P₂T₁

V₂ = (80 × 50 × 879)/(100 × 293)

V₂ = (80 × 50 × 879)/(100 × 293)

V₂ = 120cm³

(3ci)
An exothermic reaction is a chemical reaction that releases heat energy into the surroundings, often resulting in an increase in temperature.

(3cii)
(Draw the diagram)

=======================

(4ai)
A weak acid does not ionize completely in water, meaning only a small fraction of the acid molecules dissociate into ions while a strong acid ionizes completely in water, dissociating all of its molecules into ions.

(4aii)
A concentrated acid has a large amount of acid dissolved in a small volume of water while a dilute acid has a small amount of acid dissolved in a large volume of water.

(4bi)
NH₄Cl is an ammonium salt. When it dissolves in water, it dissociates to form NH₄⁺ and Cl⁻ ions. The NH₄⁺ ion acts as a weak acid and dissociates slightly, releasing H⁺ ions, which lowers the pH of the solution.

(4bii)
H₂SO₄ is a strong acid, which dissociates completely in solution, producing more ions and therefore has higher conductivity. CH₃COOH is a weak acid and only partially dissociates, producing fewer ions and resulting in lower conductivity.

(4ci)
Calcium (Ca); +2
Oxygen (O); -2
Silicon (Si); x

(+2) + x + 3(-2) = 0
+2 + x – 6 = 0
x – 4 = 0
x = +4

The oxidation number of silicon in CaSiO₃ is +4.

(4cii)
Oxygen can be prepared from air by fractional distillation. Air is first filtered and compressed, then cooled to a very low temperature (around -200°C) using liquid nitrogen or liquid oxygen. The compressed air is then allowed to expand, causing the temperature to drop further. The air is then separated into its components, including oxygen, nitrogen, and argon, based on their boiling points. Oxygen is collected and stored in cylinders.

(4ciii)
Limestone (CaCO₃) is a common ore of calcium.
=======================

(5ai)
A saturated hydrocarbon contains only single bonds between carbon atoms while an unsaturated hydrocarbon contains at least one double or triple bond between carbon atoms.

(5aii)
C₃H₄ + 4O₂ —> 3CO₂ + 2H₂O

(5aiii)
H H
| |
H₃C – C – C – H
| |
Br H
2-bromopropane

(5bi)
H H
/
C—C
// \
H-C C-H
\ //
C—C
/
H H

(5bii)
C₆H₆ + Br₂ —> C₆H₅Br + HBr

(5biii)
α-amino acid

(5biv)
Carboxylic acid (-COOH) and amine (-NH₂)

(5c)
Carbohydrates are polyhydroxy aldehydes or ketones, or substances that yield these compounds on hydrolysis.

(i) (CH₂O)ₙ (n is typically 3-7)

(ii) C₁₂H₂₂O₁₁.