Question

Gas 'A' is bubbled through slaked lime when a white precipitate is formed, on prolonged bubbling the precipitategets dissolved. On heating the resultant solution, the white precipitate reappeared with solution of gas 'B'. The gases 'A' and 'B' respectively are: (a) \(\mathrm{CO} \& \mathrm{CO}_{2}\) (b) \(\mathrm{CO}_{2} \& \mathrm{CO}_{2}\) (c) \(\mathrm{CO} \& \mathrm{CO}\) (d) \(\mathrm{CO}_{2} \& \mathrm{CO}\)

Short answer

The gases 'A' and 'B' are both \(\text{CO}_2\), so (b) \(\text{CO}_2 \& \text{CO}_2\).

Step-by-step solution

Identify Reactions with Slaked Lime

The slaked lime is chemically known as calcium hydroxide, \[ \text{Ca(OH)}_2 \]. When gas 'A' is bubbled through it, a white precipitate forms, suggesting the following reaction: \[ \text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 (\text{precipitate}) + \text{H}_2\text{O} \].This indicates that gas 'A' is \(\text{CO}_2\).

Understand the Dissolution Upon Prolonged Bubbling

When the white precipitate of calcium carbonate, \(\text{CaCO}_3\), is subjected to prolonged bubbling of gas 'A' which is \(\text{CO}_2\), it can turn into calcium bicarbonate, \(\text{Ca(HCO}_3\text{)}_2\), which is soluble, thus the precipitate dissolves:\[ \text{CaCO}_3 + \text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{Ca(HCO}_3\text{)}_2 \].

Determine Precipitate Formation Upon Heating

Upon heating, calcium bicarbonate decomposes to form calcium carbonate again as a precipitate:\[ \text{Ca(HCO}_3\text{)}_2 \xrightarrow{\text{heat}} \text{CaCO}_3 (\text{precipitate}) + \text{H}_2\text{O} + \text{CO}_2 (\text{gas 'B'}) \].This confirms gas 'B' to be \(\text{CO}_2\) as well.

Conclusion Based on Chemical Reactions

Given the chemical processes involving the formation and dissolving of precipitates, gas 'A' and gas 'B' are both \(\text{CO}_2\). Therefore, the correct answer is (b) \(\text{CO}_2\;\&\;\text{CO}_2\).

Key concepts

Gas Reactions

Gas reactions involve the interaction of gases with other substances, often leading to chemical changes. In the context of chemistry problems like the one provided, the role of gas interactions is crucial. When a gas interacts with a liquid or a solid, it can cause changes in physical states, color, or composition of the materials involved.
For example, when carbon dioxide (\(\text{CO}_2\)) is bubbled through slaked lime (\(\text{Ca(OH)}_2\)), a gas reaction occurs resulting in the formation of a solid precipitate, calcium carbonate (\(\text{CaCO}_3\)). This is an important concept because it demonstrates the ability of gases to cause visible and chemical changes in reactions.
Understanding how gases behave in reactions helps us identify the specific gases involved based on the observed products. The original exercise specifically required recognizing that the white precipitate was due to a gas reaction involving \(\text{CO}_2\).

• Gases can form substances if conditions are right, such as via bubbling through a liquid.
• Gases involved in reactions can change or decompose to form new gases.
• Tracking the observed changes helps identify which gases are present.

Slaked Lime Reactions

Slaked lime, chemically known as calcium hydroxide (\(\text{Ca(OH)}_2\)), is commonly used in chemistry due to its reaction properties. When gases are passed through slaked lime, they often produce distinct changes because \(\text{Ca(OH)}_2\) is highly reactive.
In our exercise, \(\text{CO}_2\) gas passing through slaked lime causes the production of a white precipitate, calcium carbonate (\(\text{CaCO}_3\)). This reaction showcases the ability of slaked lime to bring about a change when exposed to particular gases.
Further on, if bubbling is continued, the precipitate dissolves, showcasing slaked lime's further interaction with \(\text{CO}_2\) to form a soluble product, calcium bicarbonate (\(\text{Ca(HCO}_3\text{)}_2\)). Slaked lime reactions are an essential area in chemistry as they highlight the conversion of gases into solids and then back into a dissolved form under certain conditions.
Understanding slaked lime reactions helps us to predict and recognize various product formations in gas reactions. This knowledge is particularly useful when assessing chemical processes in lab settings.

• Calcium hydroxide is reactive and forms precipitates upon exposure to specific gases.
• Prolonged exposure to the same gas can dissolve the initial precipitate.
• Reactions with slaked lime indicate the potential for reversible and complex transformations.

Calcium Carbonate Formation

Calcium carbonate (\(\text{CaCO}_3\)) plays an important role in many chemical reactions and is often observed in gas reactions as a white precipitate. This compound is formed when carbon dioxide gas reacts with calcium hydroxide, a classic reaction that is often used to identify the presence of \(\text{CO}_2\) in chemistry.
In the context of the exercise, the initial bubbling of \(\text{CO}_2\) through slaked lime results in the formation of \(\text{CaCO}_3\), marking the first step of the gas reaction. The production of \(\text{CaCO}_3\) shows the capacity of gas reactions to produce visible results, such as precipitates, that help us determine what has occurred chemically.
After further reaction processes, such as continued bubbling or heating, calcium carbonate can transform back from its dissolved form, calcium bicarbonate, to its solid form. This reversible transformation highlights the significance of temperature and reaction conditions on \(\text{CaCO}_3\) formation and dissolution.
Understanding calcium carbonate formation enhances our ability to manipulate and predict outcomes in chemical reactions involving gases and liquids. It is a fundamental concept used across various chemistry disciplines, including environmental science and industrial applications.

• \(\text{CaCO}_3\) is commonly formed through reactions with carbon dioxide.
• Precipitates can dissolve and re-form based on chemical environments.
• Reaction conditions such as temperature significantly affect \(\text{CaCO}_3\) stability.