2023 - JAMB Chemistry Past Questions and Answers - page 2

The valency of an element is determined by the number of electrons it needs to gain or lose to achieve a stable, noble gas electron configuration. 

For the element with the electronic configuration 2, 8, 7:

- The first two electrons fill the first energy level (1s²).
- The next eight electrons fill the second energy level (2s² 2p⁶).
- The remaining seven electrons are in the third energy level (3s² 3p⁶ 3d¹).

The element is in Group 17 (Group VIIA) of the periodic table, which includes the halogens. Elements in this group typically have a valency of 1 by gaining one electron to achieve a stable configuration.

Therefore, the correct answer is 1

A more detailed explanation of why non-metals tend to gain electrons in chemical reactions:

1. Electron Affinity: Non-metals generally have a higher electron affinity, which means they have a greater tendency to gain electrons. Electron affinity is the energy change that occurs when an electron is added to a neutral atom to form a negative ion (anion).

2. Electronegativity: Non-metals typically have higher electronegativity values compared to metals. Electronegativity is a measure of an atom's ability to attract and hold onto electrons in a chemical bond. Non-metals, being more electronegative, have a tendency to attract electrons toward themselves.

3. Formation of Anions: In chemical reactions, non-metals often form negative ions (anions) by gaining electrons. This behaviour allows them to achieve a stable electron configuration similar to that of noble gases. By gaining electrons, non-metals can fill or complete their outer electron shells.

4. Ionic Bonds in Compounds: Non-metals and metals often form ionic compounds through the transfer of electrons. In these compounds, non-metals acquire electrons from metals, leading to the formation of negatively charged ions (anions). The attraction between positively charged metal ions (cations) and negatively charged non-metal ions results in the ionic bond.

In summary, the tendency of non-metals to gain electrons is deeply rooted in their electron affinity and electronegativity, ultimately leading to the formation of negatively charged ions in various chemical reactions.

A colloid is a type of mixture where one substance is dispersed evenly throughout another substance. The dispersed particles are usually larger than those in a solution but smaller than those in a suspension. The mixture appears homogeneous at first glance but may separate into distinct phases over time.

Among the options provided: Milk is an example of a colloid. In milk, tiny fat globules are dispersed throughout the liquid, creating a colloid. The dispersed particles are larger than individual molecules but do not settle out like in a suspension.

In a neutral compound, the sum of the oxidation numbers of all the elements is always equal to zero.

Therefore, the correct answer is 0.

Filtration involves passing water through a porous material or a filter, which can trap and remove suspended particles, solids, and larger impurities from the water.

Therefore, the correct answer is: Filtration

Ionic bonding occurs when one atom donates electrons (forming a positive ion or cation), and another atom accepts those electrons (forming a negative ion or anion). The resulting ions have opposite charges and are held together by electrostatic forces.

Therefore, the correct answer is: Ionic bonding.

Rust is a common name for a very common compound, iron oxide. Specifically, rust refers to the reddish-brown substance that forms on the surface of iron or steel when it reacts with oxygen and moisture in the presence of air. The chemical process through which this corrosion occurs is known as oxidation.

The primary chemical formula for rust is **Fe₂O₃**, but the exact composition can vary. Rust is often a mixture of iron oxides and hydroxides, and it's commonly represented as a hydrated iron(III) oxide, denoted as \(Fe_2O_3 \cdot nH_2O\), indicating the presence of water molecules.

The formation of rust can be represented by the following simplified chemical equation:

\[ 4Fe + 3O_2 + 6H_2O \rightarrow 4Fe(OH)_3 \]

This process is accelerated by the presence of electrolytes (such as salts) and is commonly observed on objects made of iron or steel exposed to the atmosphere, especially in humid conditions. Rusting is a significant concern as it can weaken structures and objects made of iron or steel over time.

Brass is an alloy primarily composed of copper (Cu) and zinc (Zn). The proportion of copper to zinc can vary, resulting in different types of brass with varying properties. Zinc is the main alloying element that imparts specific characteristics to brass, such as increased strength, corrosion resistance, and ease of casting.

Therefore, the correct answer is: Zinc.

To balance the redox reaction, we need to ensure that the number of atoms of each element and the total charge are the same on both sides of the equation. In this reaction, we can see that the number of oxygen (O) atoms is not balanced. To balance them, we need to add a coefficient of 2 in front of CO\(_2\) to get 2CO\(_2\). Similarly, the number of iron (Fe) atoms is not balanced. To balance them, we need to add a coefficient of 2 in front of Fe to get 2Fe

Copper exhibits various oxidation states, including +1 and +2, which contribute to the formation of colourful compounds. Copper compounds are commonly used in pigments, such as copper(II) sulfate (CuSO₄), which imparts a blue colour.

Therefore, the correct answer is Copper (Cu).