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Difficulty: MediumOxides of Carbon and Trioxocarbonate(IV) Salts

A 50.0 cm350.0\text{ cm}^3 gaseous mixture consisting of equal volumes of carbon(II) oxide and carbon(IV) oxide is passed through an excess solution of concentrated potassium hydroxide. What volume of gas remains unabsorbed, and which oxide of carbon was removed from the mixture?

  1. 25.0 cm325.0\text{ cm}^3, with carbon(IV) oxide being removedAnswer
  2. B
    25.0 cm325.0\text{ cm}^3, with carbon(II) oxide being removed
  3. C
    50.0 cm350.0\text{ cm}^3, with neither gas being removed
  4. D
    0.0 cm30.0\text{ cm}^3, with both gases being removed

Answer

25.0 cm325.0\text{ cm}^3 of gas remains unabsorbed, with carbon(IV) oxide being the component removed by potassium hydroxide solution.
Carbon(IV) oxide (CO2\text{CO}_2) is an acidic oxide that dissolves and reacts with concentrated alkali solutions such as potassium hydroxide to form potassium trioxocarbonate(IV) and water. Since the mixture contains 25.0 cm325.0\text{ cm}^3 of CO2\text{CO}_2 and 25.0 cm325.0\text{ cm}^3 of neutral carbon(II) oxide (CO\text{CO}), only CO2\text{CO}_2 is absorbed, leaving 25.0 cm325.0\text{ cm}^3 of CO\text{CO} gas remaining.

Step-by-Step Solution

1
Determine the initial volume of each gas component in the mixture.
The mixture has 50.0 cm350.0\text{ cm}^3 total volume with equal proportions, giving 25.0 cm325.0\text{ cm}^3 of CO\text{CO} and 25.0 cm325.0\text{ cm}^3 of CO2\text{CO}_2.
Equal volume proportions mean each gas makes up half of the total volume.
2
Analyze the reaction of each gas with concentrated potassium hydroxide (KOH\text{KOH}) solution.
CO2\text{CO}_2 reacts via 2KOH(aq)+CO2(g)→K2CO3(aq)+H2O(l)2\text{KOH(aq)} + \text{CO}_2\text{(g)} \rightarrow \text{K}_2\text{CO}_3\text{(aq)} + \text{H}_2\text{O(l)}, absorbing all 25.0 cm325.0\text{ cm}^3 of CO2\text{CO}_2. CO\text{CO} does not react.
CO2\text{CO}_2 is an acidic oxide which neutralizes alkali solutions, whereas CO\text{CO} is a neutral oxide.
3
Calculate the unabsorbed volume of gas.
25.0 cm325.0\text{ cm}^3 of CO\text{CO} remains as unabsorbed gas.
Subtracting the absorbed volume of CO2\text{CO}_2 (25.0 cm325.0\text{ cm}^3) from total volume (50.0 cm350.0\text{ cm}^3) leaves 25.0 cm325.0\text{ cm}^3.

Key Concept

Chemical Behavior of Oxides of Carbon toward Alkalis
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Topics

Oxides of Carbon and Trioxocarbonate(IV) Salts

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