Posted on: 04:47 Sat, 21 Jun 2025

CHEMISTRY PAPER I QUESTIONS:-








CHEMISTRY THEORY ANSWER:-

(1)
(a) Neutralisation
(b) Redox
(c) Precipitation
(d) Redox
(e) Precipitation

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(2)
(PICK ANY FIVE)
(i) Magnesium hydroxide [Mg(OH)?]: Used as an antacid and laxative in medicine to neutralize excess stomach acid and relieve constipation.

(ii) Calcium carbonate [CaCO?]: Used in the manufacture of cement, and as a filler in paper, paint, and plastics industries. It is also used in agriculture to neutralize acidic soils (agricultural lime).

(iii) Barium sulfate [BaSO?]: Used in medical imaging for X-ray contrast of the digestive tract due to its opacity to X-rays and its non-toxic nature when insoluble.

(iv) Calcium oxide [CaO]: Known as quicklime, it is used in steel making, flue gas treatment, and soil stabilization in construction.

(v) Magnesium sulfate [MgSO?]: Also known as Epsom salt, used in medicine to treat muscle cramps, in agriculture to correct magnesium-deficient soil, and as a drying agent in organic synthesis.

(vi) Strontium nitrate [Sr(NO?)?]: Used in fireworks and signal flares to produce a bright red flame due to strontium ions.

(vii) Calcium chloride [CaCl?]: Used for de-icing roads, moisture absorption (as a drying agent), and in refrigeration brines.

(viii) Barium chloride [BaCl?]: Used in laboratory testing to test for sulfate ions in chemical analysis.

(ix) Calcium hydroxide [Ca(OH)?]: Also known as slaked lime, used in water treatment, wastewater neutralization, and food processing (e.g., in the preparation of corn tortillas).

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(3a)
True

(3b)
False

(3c)
True

(3d)
True

(3e)
True

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(4)
AlCl? is a salt formed from a weak base and a strong acid. When it dissociates in water, we have Aluminum, Chloride, hydrogen and hydroxide ions in the solution. The hydroxide ions are removed since Aluminum hydroxide is a weak base.
The hydrogen ions are not removed because hydrochloric acid is a strong acid and is completely ionized in solution. There is an excess of hydrogen ions, causing the solution to be acidic.

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(5)


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(6)
(a) NH? – Trigonal pyramidal
(b) NH?? – Tetrahedral
(c) BCl? – Trigonal planar
(d) CO? – Linear
(e) H?O – Bent (or V-shaped)

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(8)


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(9a)
A = Oxygen (O?)
B = Calcium oxide (CaO)

(9b)
(i) 2Ca(s) + O?(g) –> 2CaO(s)
(ii) CaO(s) + H?O(l) –> Ca(OH)?(aq)

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(10a)
A battery is a device that converts chemical energy into electrical energy using redox (oxidation-reduction) reactions. It consists of one or more electrochemical cells made up of two electrodes and an electrolyte.

(10b)
At the anode (oxidation):
Zn(s) –> Zn²?(aq) + 2e?

At the cathode (reduction):
Cu²?(aq) + 2e? –> Cu(s)

In an electrochemical cell, a redox reaction occurs where one substance is oxidised and another is reduced, allowing electricity to be generated. For example, in a cell containing zinc and copper, zinc metal at the anode loses two electrons to form Zn²? ions — this is oxidation. The electrons released by zinc then travel through an external circuit to the copper electrode, where Cu²? ions in the solution gain those electrons and are reduced to copper metal, which deposits on the cathode. These two half-reactions happen simultaneously. As the electrons flow from zinc to copper, electrical energy is produced. The overall redox reaction for the cell is:

Zn(s) + Cu²?(aq) –> Zn²?(aq) + Cu(s)

This process shows how a redox reaction, with both oxidation and reduction happening together, drives the flow of electrons that we use as electricity.

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(12)







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