To obtain pure carbon(ii)oxide from its mixture with carbon(iv)oxide, the mixture should be?

Analysis

The question asks for a chemical method to separate Carbon(II) oxide ($CO$) from a mixture containing Carbon(IV) oxide ($CO_2$). The key is to identify a substance that will react with one gas but not the other.

Concept Explanation

• Carbon(IV) oxide ($CO_2$): This is an acidic oxide. It reacts readily with alkaline solutions (bases) to form carbonates and water.
• Carbon(II) oxide ($CO$): This is a neutral oxide. It does not react with bases like sodium hydroxide ($NaOH$).

To separate the two, we need a "scrubber"—a substance that will absorb the $CO_2$ while allowing the $CO$ to pass through unaffected.

Step-by-Step Solution

1. Evaluate the options: • A (Heated Copper(II) oxide): $CO$ reacts with heated $CuO$ to form $CO_2$ and $Cu$. This would convert your $CO$ into $CO_2$, which is the opposite of what you want. • B (Water): $CO_2$ is slightly soluble in water to form carbonic acid, but this is not an efficient way to remove it completely from a gas mixture. • C (Conc. $H_2SO_4$): Concentrated sulfuric acid is a drying agent. It removes water vapor but does not react with $CO_2$. • D (Conc. $NaOH$): Sodium hydroxide is a strong base. When the mixture is bubbled through it, the $CO_2$ reacts according to the following equation: $2NaOH_{(aq)} + CO_{2(g)} \rightarrow Na_2CO_{3(aq)} + H_2O_{(l)}$ The $CO_2$ is trapped in the solution as sodium carbonate, while the $CO$ gas passes through the solution unchanged.

2. Conclusion: Bubbling the mixture through concentrated $NaOH$ is the standard laboratory method for removing $CO_2$ impurities from $CO$.

Correct Answer

The correct option is D.

Exam Tip

Whenever you see a question asking to remove an acidic gas (like $CO_2$, $SO_2$, or $H_2S$) from a mixture, always look for an alkaline solution (like $NaOH$ or $KOH$) as your answer. They act as chemical "sponges" for acidic gases!