Chemistry 2023 Jamb Examination

The maximum number of electrons in a given energy level is calculated using the formula \( 2n^2 \), where n is the principal quantum number.
For n = 2:\[ 2n^2 = 2(2^2) = 2 \times 4 = 8 \]Therefore, the second energy level can hold a maximum of 8 electrons.

Phenolphthalein is commonly used as an indicator in titrations involving bases.
It is colourless in acidic solutions and turns pink in basic solutions, making it ideal for identifying the presence of bases.
Methyl orange is suitable for strong acid-weak base titrations, bromothymol blue changes colour over a pH range 6-7, and litmus paper is less precise but also indicates bases.

The ideal gas law \( PV = nRT \) requires temperature to be in Kelvin (K) because the law is based on absolute temperature.
Using Celsius or Fahrenheit would lead to incorrect calculations as these scales do not start at absolute zero.

Chlorine is used in the production of chlorofluorocarbons (CFCs) which are compounds containing chlorine, fluorine, and carbon.
CFCs were historically used as refrigerants and propellants. Chlorine is not directly involved in the synthesis of methane, ammonia, or ethanol.

Rusting involves the reaction of iron with oxygen and water to form hydrated iron(III) oxide (Fe2O3·xH2O).
This oxide is basic in nature because it can react with acids to form salts and water, hence rusting leads to the formation of a basic oxide.

A primary cell is a non-rechargeable battery that cannot be reused once its chemical reactants are exhausted.
An alkaline battery is a primary cell because it is intended for single use, whereas nickel-cadmium, lead-acid, and lithium-ion batteries are secondary (rechargeable) cells.

Acids react with many metals, especially those above hydrogen in the reactivity series, to produce hydrogen gas.
For example, hydrochloric acid reacts with zinc: \( Zn + 2HCl \rightarrow ZnCl_2 + H_2 \).
Acids turn blue litmus red, taste sour, and have a pH below 7, not above.

The lanthanides and actinides are f-block elements because their electrons are filling the 4f and 5f orbitals respectively.
These elements are typically placed below the main body of the periodic table to keep the table more compact.

CCl4 consists of one carbon atom bonded to four chlorine atoms.
The systematic IUPAC name is tetrachloromethane, following the convention for naming compounds with one central carbon atom and four identical substituents.

The melting and boiling points of pure substances vary depending on their molecular structure, intermolecular forces, and bonding.
Substances with strong intermolecular forces typically have higher melting and boiling points, while those with weak forces have lower values.
Therefore, there is no single rule; it depends on the specific substance.