2023 - JAMB Chemistry Past Questions and Answers - page 4

The principal ore of iron, from which iron is extracted, is Hematite.

Hematite (Fe2O3) is a common iron ore and is the primary source of iron for the iron and steel industry. It is often found in sedimentary rocks and is characterized by its silver to black metallic luster.

The type of reaction involved in the formation of alkanols from alkenes is Addition reaction.

In the presence of water or steam and typically under specific conditions such as high temperature and pressure, alkenes undergo an addition reaction, leading to the formation of alkanols (alcohols). In this reaction, the double bond in the alkene is broken, and a hydroxyl (-OH) group is added to each carbon of the former double bond.

The general reaction is:

\[ \text{Alkene} + \text{Water} \rightarrow \text{Alkanol} \]

According to Boyle's Law, the relationship between pressure and volume for a given amount of gas at constant temperature is expressed as \( P_1V_1 = P_2V_2 \).

Given:
- \( P_1 = 2.0 \) atm
- \( V_1 = 4.0 \) L
- \( P_2 = 1.0 \) atm (new pressure, reduced)
- \( V_2 \) is what we need to find.

Using the Boyle's Law formula, we can rearrange it to solve for \( V_2 \):
\[ V_2 = \frac{{P_1 \cdot V_1}}{{P_2}} \]

Substitute the given values:
\[ V_2 = \frac{{2.0 \, \text{atm} \cdot 4.0 \, \text{L}}}{{1.0 \, \text{atm}}} \]
\[ V_2 = 8.0 \, \text{L} \]

Therefore, the new volume of the gas at 1.0 atm pressure is 8.0 L

The rate of a chemical reaction is influenced by various factors:

- Concentration of reactants: Higher concentration generally leads to a faster reaction.

- Presence of a catalyst: A catalyst can increase the rate of a reaction by providing an alternative reaction pathway with lower activation energy.

- Temperature: Increasing temperature usually accelerates reaction rates by providing more kinetic energy to the particles, leading to more frequent and energetic collisions.

However, the molecular weight of products is not a direct factor affecting the rate of the reaction. The focus is typically on the characteristics of reactants and the conditions under which the reaction occurs.

Therefore, the correct answer is the molecular weight of products.

Stainless steel typically contains iron as the base metal and chromium as the main alloying element. Chromium contributes to the corrosion resistance and other properties that make stainless steel highly resistant to rust and staining.

Therefore, the correct answer is Iron and Chromium.

According to Graham's law of diffusion, the ratio of the diffusion rates of two gases is the inverse of the square root of the ratio of their molar masses. Therefore:

\[ \text{Rate of A : Rate of B} = \sqrt{\frac{\text{Molar mass of B}}{\text{Molar mass of A}}} \]

Given:
- Molar mass of A (\(M_A\)) = 32 g/mol
- Molar mass of B (\(M_B\)) = 64 g/mol

\[ \text{Rate of A : Rate of B} = \sqrt{\frac{64 \, \text{g/mol}}{32 \, \text{g/mol}}} = \sqrt{2} \]

So, the correct ratio of their diffusion rates is approximately 2:1.

The correct calculation for the mass of 500 mL of ethanol would be:

\[ \text{Mass} = \text{Volume} \times \text{Density} \]

Given:
- Volume of ethanol = 500 mL
- Density of ethanol = 0.789 g/mL

\[ \text{Mass} = 500 \, \text{mL} \times 0.789 \, \text{g/mL} = 394.5 \, \text{g} \]

To calculate the mass of a substance, you can use the formula: \(\text{Mass} = \text{Volume} \times \text{Density}\). Given the volume of ethanol is 500 mL and the density of ethanol is 0.789 g/mL, you can plug the values into the formula:

\[ \text{Mass} = 500 \, \text{mL} \times 0.789 \, \text{g/mL} = 394.5 \, \text{g} \]

The planetary model, also known as the Bohr model, is a simple representation of the structure of an atom proposed by Niels Bohr in 1913. This model was developed to address the limitations of the earlier Rutherford model.

Despite its own (Bohr model) limitations, the Bohr model laid the foundation for later quantum mechanical models that provide a more accurate understanding of atomic structure.

- Salt: Hygroscopic - Absorbs moisture from the air.
- Sugar: Not typically hygroscopic - Does not readily absorb moisture.
- Silica gel: Hygroscopic - Often used as a desiccant to absorb moisture.
- Aluminum: Not hygroscopic - Does not have a strong affinity for moisture.

Therefore, the correct answer is Aluminum.