Question

A drying agent which absorbs \(\mathrm{CO}_{2}\) and react violently with water is (1) \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) (2) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\) (3) Conc. \(\mathrm{H}_{2} \mathrm{SO}_{4}\) (4) \(\mathrm{CaO}\)

Short answer

The correct answer is \(\text{CaO}\).

Step-by-step solution

- Identify the Properties Required

The question requires a drying agent that both absorbs \(\text{CO}_2\) and reacts violently with water. First, understand what each property involves.

- Evaluate Na2CO3

Sodium carbonate (\(\text{Na}_2\text{CO}_3\)) is not known for reacting violently with water. It dissociates in water without causing a violent reaction. Hence, this option is not correct.

- Evaluate C2H5OH

Ethanol (\(\text{C}_2\text{H}_5\text{OH}\)) does not absorb \(\text{CO}_2\) and also does not react violently with water. Thus, this option can be disregarded.

- Evaluate Conc. H2SO4

Concentrated sulfuric acid (Conc. \(\text{H}_2\text{SO}_4\)) absorbs water but does not absorb \(\text{CO}_2\). Further, while it reacts exothermically with water, it is not the most violent.

- Evaluate CaO

Calcium oxide (\(\text{CaO}\)) actively absorbs \(\text{CO}_2\) by forming calcium carbonate (\(\text{CaCO}_3\)). It also reacts violently with water by forming calcium hydroxide (\(\text{Ca(OH)}_2\)) with significant release of heat.

- Conclusion

Since \(\text{CaO}\) meets both criteria of absorbing \(\text{CO}_2\) and reacting violently with water, the correct answer is \(\text{CaO}\).

Key concepts

Drying Agents

Drying agents are compounds that readily absorb moisture from their surroundings. They are critical in both chemical reactions and everyday applications to keep substances dry. Some common drying agents include:

• Calcium oxide (CaO)
• Silica gel
• Concentrated sulfuric acid (H₂SO₄)

They are essential in ensuring that reactions do not get contaminated with water, which can interfere with outcomes or cause unwanted side reactions. In our exercise, Calcium oxide (CaO) is a drying agent that not only absorbs moisture but also absorbs CO₂ and reacts violently with water.

Chemical Reactions

Chemical reactions involve the transformation of reactants into products through the breaking and forming of chemical bonds. Generally, they can be categorized into several types such as:

• Synthesis reactions
• Decomposition reactions
• Single replacement reactions
• Double replacement reactions
• Combustion reactions

In the context of the provided exercise, the chemical reaction of Calcium oxide (CaO) with water is considered a synthesis reaction because CaO reacts with H₂O to form a new compound, calcium hydroxide (Ca(OH)₂). This reaction is both vigorous and exothermic, meaning it releases a significant amount of heat.

Properties of Compounds

Understanding the properties of chemical compounds is vital in predicting their behavior in reactions. Key properties include:

• Solubility
• Reactivity
• Stability
• Melting and boiling points

For example, knowing that Calcium oxide (CaO) has a high reactivity with water helps us predict its violent reaction and heat generation. In the solution to our exercise, this reactivity is central to identifying CaO as the correct answer. Each compound given in the options possesses distinct properties that influence their interactions with water and CO₂, ultimately guiding us to the correct drying agent.

Exothermic Reactions

Exothermic reactions are processes that release energy, usually in the form of heat, to their surroundings. This type of reaction is quite common and can be observed in everyday life, such as when you burn wood or when calcium oxide reacts with water. The general formula for an exothermic reaction can be represented as:
Reactants → Products + Energy (heat)
In our specific exercise, when Calcium oxide (CaO) reacts with water (H₂O), the reaction is exothermic and releases a large amount of heat, illustrated as:
CaO + H₂O → Ca(OH)₂ + heat
This heat release is so intense that the reaction can be considered violent. Recognizing exothermic reactions is crucial for anticipating and managing the heat produced during chemical processes.