The correct option for the question regarding the important product obtained from heating calcium hydroxide and ammonium chloride is **C. passing it through calcium oxide**. Let's break down the reasoning behind this answer and why the other options are not suitable. ### Step-by-Step Explanation 1. **Understanding the Reaction**: - When calcium hydroxide (Ca(OH)₂) is heated with ammonium chloride (NH₄Cl), a chemical reaction occurs that produces calcium chloride (CaCl₂), water (H₂O), and ammonia gas (NH₃). The reaction can be summarized as follows: \[ Ca(OH)_2 + 2NH_4Cl \rightarrow CaCl_2 + 2H_2O + 2NH_3 \] - The ammonia gas produced can be collected and is an important product of this reaction. 2. **Drying the Product**: - The question asks how to obtain the ammonia gas dry. Ammonia is a gas at room temperature and can be easily lost if not handled properly. To collect it in a dry form, we need to use a drying agent. 3. **Why Option C is Correct**: - **C. Passing it through calcium oxide**: Calcium oxide (CaO), also known as quicklime, is a strong drying agent. When ammonia gas is passed through calcium oxide, it reacts with moisture (water vapor) in the gas, effectively drying it. The reaction can be represented as: \[ CaO + H_2O \rightarrow Ca(OH)_2 \] - This reaction shows that calcium oxide absorbs water, thus ensuring that the ammonia collected is dry. ### Why the Other Options are Incorrect 1. **Option A: Dissolving it in water, recrystallizing it, and then drying in the oven**: - This option suggests dissolving the product in water and recrystallizing it. However, ammonia is a gas and does not dissolve well in water to form a solid that can be recrystallized. Instead, it would escape into the atmosphere, making this method ineffective for obtaining dry ammonia. 2. **Option B: Passing it through a concentrated aqueous solution of sodium hydroxide**: - While sodium hydroxide (NaOH) is a strong base and can absorb some gases, it is not an effective drying agent for ammonia. Instead, it would react with ammonia to form sodium amide (NaNH₂) or other products, which would not yield dry ammonia gas. Therefore, this option is not suitable. 3. **Option D: Passing it through concentrated sulfuric acid**: - Concentrated sulfuric acid (H₂SO₄) is a strong dehydrating agent, but it is not selective for ammonia. It can react with ammonia to form ammonium bisulfate (NH₄HSO₄), which would not yield dry ammonia gas. Thus, this option is also incorrect. ### Summary of Key Points - The reaction between calcium hydroxide and ammonium chloride produces ammonia gas, which needs to be collected dry. - Calcium oxide is an effective drying agent for ammonia, making option C the correct choice. - Other options either do not effectively collect ammonia or lead to unwanted reactions. ### Revision Summary - **Calcium hydroxide and ammonium chloride produce ammonia gas when heated.** - **Calcium oxide is a strong drying agent that effectively removes moisture from gases.** - **Dissolving ammonia in water or using sodium hydroxide or sulfuric acid does not yield dry ammonia.** - **Understanding the properties of reactants and products is crucial in determining the correct method for collection.**