Methanoic acid mixes with water in all proportions and has about the same boiling point as water. Which of the…

1. Analyze the Question

We have a mixture containing three components: sand (insoluble solid), water (liquid), and methanoic acid (liquid). We need to obtain pure water. The challenge is that methanoic acid and water have similar boiling points, meaning simple distillation will not effectively separate them because they will vaporize together.

2. Explain the Concept

• Filtration: This is used to separate insoluble solids from liquids. Sand is insoluble in water, so filtration will easily remove the sand.
• Neutralization: Methanoic acid ($HCOOH$) is an acid. If we add a base like sodium hydroxide ($NaOH$), a neutralization reaction occurs: $HCOOH + NaOH \rightarrow HCOONa + H_2O$ This reaction produces sodium methanoate (a salt) and water.
• Distillation: Once the acid is converted into a salt, the salt has a very high boiling point compared to water. Therefore, when you heat the mixture, only the water will vaporize, leaving the salt behind. This allows for the collection of pure water.

3. Show the Solution

• Step 1: Filtration. First, pass the mixture through a filter paper. The sand will be trapped as residue, leaving a mixture of water and methanoic acid in the filtrate.
• Step 2: Neutralization. Add sodium hydroxide ($NaOH$) to the filtrate. The $NaOH$ reacts with the methanoic acid to form sodium methanoate ($HCOONa$), which is a non-volatile salt dissolved in the water.
• Step 3: Distillation. Now, perform distillation on the solution. Since sodium methanoate does not vaporize at the boiling point of water, pure water will distill over, leaving the salt in the flask.

4. Identify the Answer

Comparing our steps to the options:

• Option A (Extractive distillation) is unnecessary and complex.
• Option B (Filtration followed by distillation) would fail because the acid would still distill with the water.
• Option C (Neutralization with sodium hydroxide followed by distillation) correctly addresses the need to remove the sand (implied in the process) and convert the acid into a non-volatile salt to allow for effective distillation.
• Option D (Neutralization followed by filtration) is incorrect because the salt produced is soluble in water and would not be removed by filtration.

5. Exam Tip

When dealing with mixtures of liquids that have similar boiling points, look for a way to change the chemical properties of one component (like turning an acid into a salt) to make it non-volatile. This makes the subsequent distillation process much more effective!