2023 - JAMB Chemistry Past Questions and Answers - page 3

According to Boyle's Law, for a given amount of gas at constant temperature, the pressure and volume are inversely proportional. Mathematically, Boyle's Law is represented as:

\[ P_1 \cdot V_1 = P_2 \cdot V_2 \]

Where:
- \(P_1\) and \(V_1\) are the initial pressure and volume.
- \(P_2\) and \(V_2\) are the final pressure and volume.

In this case:
- \(P_1 = 2\) atmospheres
- \(V_1 = 1.5\) liters
- \(P_2 = 4\) atmospheres

Let's solve for \(V_2\):

\[ 2 \cdot 1.5 = 4 \cdot V_2 \]

\[ V_2 = \frac{2 \cdot 1.5}{4} \]

\[ V_2 = 0.75 \, \text{liters} \]

Therefore, the correct answer is:

0.75 liters

In the presence of a suitable catalyst, alkynes can undergo hydrogenation reactions, where hydrogen atoms are added across the carbon-carbon triple bond, resulting in the formation of alkanes.

The reaction is represented as:

\[ \text{Alkyne} + \text{H}_2 \text{ (in the presence of a catalyst)} \rightarrow \text{Alkane} \]

Therefore, the correct answer is:

Hydrogen gas (H₂)

The conversion of benzene to its derivative toluene by the addition of a methyl group is an example of an Electrophilic substitution reaction.

In this case, an electrophile (a methyl cation) substitutes for one of the hydrogen atoms in the benzene ring. This type of reaction is a characteristic feature of aromatic compounds like benzene, where the substitution occurs via electrophilic attack on the aromatic ring.

The general reaction is:

\[ \text{Benzene} + \text{Methyl group} \rightarrow \text{Toluene} \]

Therefore, the correct answer is: Electrophilic substitution

To determine the empirical formula, we need to find the simplest whole-number ratio of the atoms in the compound.

Let's assume we have 100 grams of the compound to make percentage to mass conversions easier.

- Carbon: \(40.00\% \rightarrow 40.00 \, \text{g}\)
- Hydrogen: \(6.67\% \rightarrow 6.67 \, \text{g}\)
- Oxygen: \(53.33\% \rightarrow 53.33 \, \text{g}\)

Next, we need to find the mole ratios by dividing each mass by the molar mass of the respective element.

- Moles of Carbon: \(\frac{40.00 \, \text{g}}{12.01 \, \text{g/mol}} \approx 3.33\)
- Moles of Hydrogen: \(\frac{6.67 \, \text{g}}{1.01 \, \text{g/mol}} \approx 6.60\)
- Moles of Oxygen: \(\frac{53.33 \, \text{g}}{16.00 \, \text{g/mol}} \approx 3.33\)

Now, we find the simplest whole-number ratio by dividing each mole value by the smallest of the three:

- Carbon: \(\frac{3.33}{3.33} \approx 1\)
- Hydrogen: \(\frac{6.60}{3.33} \approx 2\)
- Oxygen: \(\frac{3.33}{3.33} \approx 1\)

The ratio is \(1:2:1\), suggesting the empirical formula is \(CH_2O\).

Therefore, the correct answer is: CH₂O

Alkanals, also known as aldehydes, are organic compounds that have a carbonyl group (C=O) bonded to a hydrogen atom and are located at the end of a carbon chain. The general structure of an alkanal is RCHO, where R represents an alkyl group.

Therefore, the correct answer is: Carbonyl group (C=O).

Carbon monoxide is produced as a byproduct of incomplete combustion of carbon-containing fuels. In urban settings, vehicles, especially those powered by internal combustion engines, release carbon monoxide into the air as part of their exhaust gases. Poorly tuned engines, inefficient combustion, or inadequate ventilation contribute to higher concentrations of CO in areas with heavy traffic.

Therefore, the correct answer is Vehicle emissions.

In the given reaction:

\[ \text{Zn + CuSO}_4 \rightarrow \text{ZnSO}_4 + \text{Cu} \]

The reducing agent is the substance that undergoes oxidation, losing electrons in the process. In this reaction, zinc (Zn) is oxidized:

\[ \text{Zn} \rightarrow \text{Zn}^{2+} + 2\text{e}^- \]

Here, zinc (Zn) loses electrons and is oxidized to form zinc ions (\(Zn^{2+}\)).

Therefore, the reducing agent in this reaction is Zn.

Carbon dioxide is a greenhouse gas, meaning it has the ability to trap heat in the Earth's atmosphere. Human activities, such as burning fossil fuels and deforestation, contribute to the increase in carbon dioxide levels, enhancing the greenhouse effect and leading to global warming and climate change.

The same number of protons but different/same numbers of neutrons.

Isotopes of an element have the same number of protons (which defines the element) but different numbers of neutrons.

This results in isotopes having different atomic masses. The number of protons in an atom determines its element and chemical properties, while the number of neutrons can vary among isotopes of the same element. Isotopes of an element share the same number of electrons, ensuring they have the same chemical behaviour.

A calorimeter is a scientific instrument used to measure the heat exchange in chemical reactions or physical processes. It allows for the accurate measurement of the heat absorbed or released during a reaction by isolating the reaction from the external environment.

Therefore, the correct answer is Calorimeter.