Chemistry 2021 Jamb Examination

To find the number of moles, use the relation:\[ \text{Moles} = \dfrac{\text{Mass}}{\text{Molar Mass}} \]The molar mass of CO₂ = 12 + (16 × 2) = 44 g mol⁻¹.\[ \text{Moles} = \dfrac{220}{44} = 5 \]Hence, 220 g of carbon dioxide contains 5 moles.

Argon (Ar) is the most abundant noble gas in Earth's atmosphere, making up about 0.93% by volume. It is produced naturally through the radioactive decay of potassium-40.
Helium and neon are less abundant, while xenon is extremely rare in the atmosphere.

Deoxyribonucleic acid (DNA) carries the genetic information that determines inherited traits in all living organisms. It contains specific sequences of nucleotides called genes that code for proteins and traits.
RNA plays a role in protein synthesis, but DNA is the primary hereditary material.

Thermal capacity (also known as heat capacity) is the amount of heat energy required to raise the temperature of a body by 1 kelvin (K).
Specific heat, on the other hand, is the heat required to raise the temperature of unit mass of a substance by 1 K.

A normal hydrogen atom (protium) has only one proton in its nucleus and no neutrons. Its single electron orbits this proton.
Other isotopes of hydrogen, such as deuterium and tritium, contain one and two neutrons respectively.

Iron (Fe) is used to displace copper from copper sulphate solution because it is more reactive than copper.
The reaction is:\[ \text{Fe} + \text{CuSO}_4 \rightarrow \text{FeSO}_4 + \text{Cu} \]Thus, copper is deposited as a solid while iron goes into solution.

The nucleus of an atom is composed of protons and neutrons, collectively known as nucleons. These particles account for nearly all the mass of the atom.
Electrons orbit the nucleus in energy levels and are not part of the nucleus.

Mass by mass percentage is given by:\[ \text{Mass %} = \dfrac{\text{Mass of solute}}{\text{Mass of solute + Mass of solvent}} \times 100 \]\[ = \dfrac{20}{20 + 180} \times 100 = \dfrac{20}{200} \times 100 = 10\% \]Hence, the concentration of the solution is 10%.

Copper (Cu) has strong antibacterial and antimicrobial properties. It disrupts microbial cell membranes and interferes with essential enzymatic processes, leading to cell death.
For this reason, copper is often used in medical instruments and water purification systems.

An element with atomic number 17 is chlorine (Cl). The element with atomic number 35 is bromine (Br).
Both chlorine and bromine belong to Group 17 (the halogens) and exhibit similar chemical properties such as forming salts with metals and existing as diatomic molecules.