Which of the following substances is not a mixture?

Here are the solutions to the questions from the image:

1. Consider the following chemical equation:

$$\text{MgCl}_2 \cdot 6\text{H}_2\text{O} \to \text{MgCl}_2 + 6\text{H}_2\text{O}$$

The reaction represented by the equation is

• Step 1: Analyze the given reaction. The reactant is a hydrated salt, magnesium chloride hexahydrate ($\text{MgCl}_2 \cdot 6\text{H}_2\text{O}$). The products are anhydrous magnesium chloride ($\text{MgCl}_2$) and water ($\text{H}_2\text{O}$).
• Step 2: Identify the process. The reaction shows the removal of water of crystallization from a hydrated compound. This process is known as dehydration.
• Step 3: Compare with the given options.
  • A. Hydrolysis: Reaction with water to break a compound.
  • B. Hydration: Addition of water.
  • C. Neutralization: Reaction between an acid and a base.
  • D. Dehydration: Removal of water. The correct option is D.
• D) dehydration

2. The preparation of carbon(II) oxide is done in a fume cupboard because the gas is

• Step 1: Identify carbon(II) oxide. Carbon(II) oxide is the chemical name for carbon monoxide ($\text{CO}$).
• Step 2: Recall the properties of carbon monoxide. Carbon monoxide is a colorless, odorless, and highly poisonous gas.
• Step 3: Determine why a fume cupboard is necessary. Due to its poisonous nature, carbon monoxide must be handled in a fume cupboard to prevent inhalation and ensure safety. The correct option is B.
• B) poisonous

3. Which of the following substances is not a mixture?

• Step 1: Define a mixture. A mixture is a substance containing two or more different substances that are not chemically bonded together.
• Step 2: Evaluate each option:
  • A. Iron rod: An iron rod is primarily composed of the element iron. While commercial iron might contain impurities or be an alloy (which is a mixture), in the context of these options, pure iron is an element, not a mixture.
  • B. Urine: A complex biological fluid containing water, urea, salts, and other dissolved substances, making it a mixture.
  • C. Sea water: A solution of various salts (like sodium chloride) dissolved in water, making it a mixture.
  • D. Brine: A concentrated solution of salt (usually sodium chloride) in water, making it a mixture.
• Step 3: Conclude which is not a mixture. Among the given options, an iron rod (representing the element iron) is the only one that is not inherently a mixture. The correct option is A.
• A) Iron rod

4. Carbon(IV) oxide could be produced from glucose by

• Step 1: Identify carbon(IV) oxide. Carbon(IV) oxide is carbon dioxide ($\text{CO}_2$).
• Step 2: Consider the processes that produce $\text{CO}_2$ from glucose ($\text{C}_6\text{H}_{12}\text{O}_6$).
  • Fermentation: This is an anaerobic process where microorganisms convert glucose into ethanol and carbon dioxide (e.g., alcoholic fermentation: $\text{C}_6\text{H}_{12}\text{O}_6 \to 2\text{C}_2\text{H}_5\text{OH} + 2\text{CO}_2$).
  • Oxidation (Cellular Respiration): Glucose is oxidized to $\text{CO}_2$ and water in the presence of oxygen.
  • Decarboxylation: A specific reaction where a carboxyl group is removed, releasing $\text{CO}_2$. This is a step within broader processes like fermentation or respiration.
• Step 3: Choose the most appropriate option. While oxidation and decarboxylation are involved, fermentation is a direct and common biological process specifically known for producing $\text{CO}_2$ from glucose. The correct option is C.
• C) fermentation

5. If carbon forms $\text{CX}_4$ and $\text{CY}_2$ with elements X and Y respectively, the formula of the compound that would be formed between elements X and Y is

• Step 1: Determine the valency of element X. In $\text{CX}_4$, carbon (valency 4) combines with four atoms of X. This means X has a valency of 1.
• Step 2: Determine the valency of element Y. In $\text{CY}_2$, carbon (valency 4) combines with two atoms of Y. This means Y has a valency of 2.
• Step 3: Determine the formula of the compound formed between X (valency 1) and Y (valency 2). Using the criss-cross method, the valency of X (1) becomes the subscript for Y, and the valency of Y (2) becomes the subscript for X.
• Step 4: Write the formula. The compound formed would be $\text{X}_2\text{Y}$. The correct option is D.
• D) $\text{X}_2\text{Y}$

6. When the pressure on $200 \text{ cm}^3$ of a gas is doubled, and its absolute temperature is halved, its volume would become

• Step 1: State the combined gas law formula. $$\frac{P_1V_1}{T_1} = \frac{P_2V_2}{T_2}$$ where $P$ is pressure, $V$ is volume, and $T$ is absolute temperature.
• Step 2: Identify the initial conditions ($P_1, V_1, T_1$) and final conditions ($P_2, V_2, T_2$).
  • Initial volume $V_1 = 200 \text{ cm}^3$.
  • Let initial pressure $P_1 = P$.
  • Let initial absolute temperature $T_1 = T$.
  • Final pressure $P_2 = 2P$ (pressure is doubled).
  • Final absolute temperature $T_2 = \frac{T}{2}$ (absolute temperature is halved).
  • We need to find the final volume $V_2$.
• Step 3: Substitute the values into the combined gas law equation. $$\frac{P \cdot 200}{T} = \frac{(2P) \cdot V_2}{(T/2)}$$
• Step 4: Simplify the equation to solve for $V_2$. $$\frac{200P}{T} = \frac{4P \cdot V_2}{T}$$ Multiply both sides by $T$: $$200P = 4P \cdot V_2$$ Divide both sides by $P$: $$200 = 4V_2$$ $$V_2 = \frac{200}{4}$$ $$V_2 = 50 \text{ cm}^3$$

The correct option is C.

• C) $50 \text{ cm}^3$