Chemistry 2019 Jamb Examination

Sodium plays a vital role in maintaining osmotic balance and regulating both blood pressure and blood volume in the body.
It helps control the movement of water between body compartments and ensures proper nerve and muscle function.
A deficiency or excess of sodium can lead to imbalances such as dehydration, low blood pressure, or hypertension.

Calcium reacts more readily with water than other listed metals like beryllium or magnesium.
The reactivity of Group 2 metals increases down the group, making calcium more reactive than magnesium and beryllium.
When calcium reacts with water, it forms calcium hydroxide and hydrogen gas.

Chlorine water decomposes under bright sunlight to form hydrochloric acid (HCl) and oxygen gas (O₂).
The reaction occurs because sunlight provides energy to break down the hypochlorous acid intermediate formed in water.
This photochemical reaction is represented as: 2HOCl → 2HCl + O₂.

Chlorine acts as an oxidising agent and converts iodide ions (I⁻) in the paper to iodine (I₂).
The liberated iodine reacts with starch to form the blue-black complex that is observed.
Thus, the colour change occurs through oxidation, not direct attack on the starch.

Neutral oxides are those that neither react with acids nor bases to form salts.
Nitrous oxide (N₂O), water (H₂O), and carbon monoxide (CO) are all neutral oxides.
They exhibit no acidic or basic properties under normal conditions.

The direct dissolution of SO₃ in water is avoided because it is a violently exothermic reaction.
This can cause the formation of a mist of sulphuric acid, making the process inefficient and unsafe.
Instead, SO₃ is first absorbed in concentrated H₂SO₄ to form oleum, which is then diluted with water.

According to Rutherford’s nuclear model, most of the atom’s mass is concentrated in a small nucleus which is positively charged.
Therefore, the atom is mostly empty space where most projectiles pass undeflected.
Statement D is incorrect because the nucleus is not large; it is very small compared to the atom’s total volume.

Element X (1s²2s²2p⁴) is oxygen with a valency of 2, while Y (1s²2s²2p⁶3s²3p¹) is aluminium with a valency of 3.
The compound formed balances charges by combining two aluminium atoms with three oxygen atoms.
Hence, the formula is Al₂O₃, represented here as Y₂X₃.

Using the ideal gas equation: \(\dfrac{P_1V_1}{T_1} = \dfrac{P_2V_2}{T_2}\).
Given: \(P_2 = 2P_1\), \(V_1 = 200\,cm^3\), \(V_2 = 150\,cm^3\), and \(T_1 = 27°C = 300K\).
Substituting: \(\dfrac{P_1 \times 200}{300} = \dfrac{2P_1 \times 150}{T_2}\).\[T_2 = \dfrac{2 \times 150 \times 300}{200} = 450K\].
Therefore, the temperature rise = 450K − 300K = 150K = 177°C (approx).

From the equation: 2CO + O₂ → 2CO₂.
2 volumes of CO require 1 volume of O₂ to form 2 volumes of CO₂.
50cm³ of CO will need 25cm³ of O₂, leaving 75cm³ of unreacted O₂.
Total volume = 50cm³ CO₂ + 75cm³ O₂ = 125cm³.