Question

One mole of substance \((\mathrm{X})\) was heated with an cxcess of water, 2 molcs of readily combustible gas were produced along with a solution which when reacted with \(\mathrm{CO}_{2}\) gas produced a white turbidity. The substance (X) could be (1) \(\mathrm{Ca}\) (2) \(\mathrm{CaII}_{2}\) (3) \(\mathrm{Ca}(\mathrm{OII})_{2}\) (4) \(\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}\)

Short answer

The substance \((X)\) is calcium (\(\text{Ca}\)).

Step-by-step solution

Understand the Reaction with Water

When the substance \((X)\) reacts with water, 2 moles of a readily combustible gas are produced. Consider typical reactions of calcium compounds with water.

Identify the Readily Combustible Gas

Hydrogen gas \((\text{H}_{2})\) is a readily combustible gas. The reaction likely produces hydrogen gas.

Write Possible Reactions

Examine the reactions of each option with water:1. \(\text{Ca} + 2 \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{H}_2\)2. \(\text{CaI}_2 + \text{H}_2\text{O} \rightarrow \text{no gas produced}\)3. \(\text{Ca(OH)}_2 + \text{H}_2\text{O} \rightarrow \text{no gas produced}\)4. \(\text{Ca(NO}_3)_2 + \text{H}_2\text{O} \rightarrow \text{no gas produced}\)

Evaluate Carbon Dioxide Test

When the solution is reacted with \(\text{CO}_2\), it produces a white turbidity, indicative of calcium carbonate \(\text{CaCO}_3\):\(\text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O}\).

Select the Correct Substance

The only substance that fits both criteria (produces hydrogen gas and reacts with \(\text{CO}_2\) to form a white turbidity) is calcium metal \(\text{Ca}\).

Key concepts

Combustible Gases

Combustible gases are types of gases that can easily catch fire and burn in the presence of oxygen. One of the most common combustible gases is hydrogen \(\text{H}_2\), which reacts explosively when ignited.
When studying chemical reactions, it is essential to identify the presence of combustible gases, as they can indicate the types of products formed. For example, in our exercise, when a substance containing calcium is heated with water, hydrogen gas is produced.
To summarize:
ul>

Combustible gases can catch fire easily.

Hydrogen is a key example of a combustible gas.

The production of hydrogen gas is an important clue in chemical identification.

Another critical point to remember is that these gases often require careful handling due to their flammable nature.

Calcium Reactions

Calcium is a versatile element that participates in several important chemical reactions, especially with water and gases. In our example, one mole of calcium reacts with two moles of water to produce calcium hydroxide and hydrogen gas: \(\text{Ca} + 2 \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{H}_2\).
This reaction confirms the production of hydrogen gas as combustible and highlights calcium's reactive nature.
Key points to remember:

• Calcium reacts with water to produce calcium hydroxide and hydrogen gas.
• This reaction is an oxidation-reduction process.
• Hydrogen gas being produced indicates the reactivity of calcium.

Additionally, this calcium reaction is fundamental in predicting the formation of other substances, such as calcium carbonate when reacting with carbon dioxide.

White Turbidity Test

The white turbidity test involves adding carbon dioxide (\text{CO}_2) to a solution to check for the formation of a cloudy or 'turbid' mixture. This turbidity often indicates the presence of calcium carbonate (\text{CaCO}_3), a white precipitate.
In the given exercise, the appearance of white turbidity when \text{CO}_2 is added to the solution confirms that calcium hydroxide is present: \(\text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O}\).
This process is critical for identifying calcium compounds.

• The white turbidity test helps identify calcium compounds.
• It involves the formation of calcium carbonate as a precipitate.
• This test confirms reactions like the formation of calcium hydroxide and its subsequent reaction with \text{CO}_2.

Ensure to always look for the characteristic white turbidity indicating calcium carbonate, especially in chemical analysis involving calcium.