Problem 11 - A Complete Resource Book in Chemistry for JEE Main

Question

Molecular mass of a volatile substance may be obtained by (a) Liebig's method (b) \(\mathrm{Kjeldhal}\) 's method (c) Duma's method (d) Victor Meyer's method

Step-by-Step Solution

Answer

The correct method is (d) Victor Meyer's method.

Step 1: Understanding the Question

We are tasked with identifying which method can be used to determine the molecular mass of a volatile substance from the given options: (a) Liebig's method, (b) Kjeldhal's method, (c) Duma's method, and (d) Victor Meyer's method.

Step 2: Analyzing Liebig's Method

Liebig's method is primarily used for the determination of carbon and hydrogen content in organic compounds. It is not specifically used to find the molecular mass of a volatile substance.

Step 3: Reviewing Kjeldhal's Method

Kjeldhal's method is used to determine the nitrogen content in organic compounds. This method does not provide information needed to find the molecular mass of a volatile substance.

Step 4: Investigating Duma's Method

Duma's method is another technique focused on nitrogen determination in organic compounds, similar to Kjeldhal's method, and is not used for finding molecular mass.

Step 5: Evaluating Victor Meyer's Method

Victor Meyer's method is specifically designed for determining the molecular mass of volatile substances. It involves the measurement of the volume of gas displaced by a vaporized sample under controlled conditions.

Key Concepts

Molecular mass determination

Determining the molecular mass of a substance is essential in chemistry, as it provides insight into the molecular structure and composition. This calculation becomes particularly crucial for volatile substances, which tend to readily evaporate or turn into gas at relatively low temperatures. For volatile substances, traditional methods of calculating molecular mass can be challenging due to their quick dispersal. However, specialized techniques like Victor Meyer's method provide accurate results by leveraging the physical properties of gases. Understanding this involves recognizing the molecular weight as the sum of the weights of all atoms in a molecule. When using Victor Meyer’s method, you take advantage of the substance's volatility to measure the gas it displaces, thereby finding the molecular mass indirectly. Applications of determining molecular mass include:

• Identifying unknown substances
• Formulating chemical reactions and predicting yields
• Understanding boiling and melting points

Overall, knowing the molecular mass helps chemists in both theoretical and practical applications in their scientific explorations.

Volatile substances

Volatile substances are compounds that evaporate easily at room temperature due to their low boiling points. This property makes them perfect candidates for specific types of analyses and experiments. Volatile substances are important in various scientific fields:

• Perfumery and fragrance industries use volatiles for their scents
• Environmental studies often examine volatile organic compounds (VOCs) that can affect air quality
• In the food industry, volatile compounds are significant for flavor and aroma

The characteristics of volatility make these substances ideal for methods like Victor Meyer's. The quick transition from liquid to gas allows precise measurement of changes in volume or pressure, aiding in molecular analysis. Handling volatile substances requires care due to their propensity to vaporize. Ensuring proper containment and understanding their chemical behavior is vital for safety and accuracy in experiments.

Gas displacement method

The gas displacement method is a technique used to measure the molecular mass of volatile substances, primarily through Victor Meyer's method. This approach involves vaporizing a known quantity of the substance and capturing the gas that it displaces. Here's how it typically works:

• A volatile liquid is heated until it fully vaporizes.
• The vapor displaces a certain volume of gas in a calibrated tube.
• The displaced volume, along with ambient pressure and temperature details, helps in calculating the molecular mass.

This method capitalizes on the principles of Avogadro’s law, which states that equal volumes of gases at the same temperature and pressure contain an equal number of molecules. Thus, by measuring the volume of gas displaced, the molecular mass of the volatile substance can be deduced. Benefits of the gas displacement method include:

• Precision in measuring gaseous volumes
• Effectiveness for substances that easily become gases
• Utilization of straightforward equipment

Overall, the gas displacement method provides a reliable way to study volatile substances, allowing chemists to gain insights that are crucial for both basic research and applied sciences.