Question

Using Victor Meyer's method, \(0.2 \mathrm{~g}\) of an organic substance displaced \(56 \mathrm{~mL}\) of air at STP. The molecular weight of the compound is: (a) 112 (b) 56 (c) 80 (d) 28

Short answer

The molecular weight of the compound is 80 g/mol (option c).

Step-by-step solution

Understanding STP and Molar Volume

Standard Temperature and Pressure (STP) are conditions of 0°C (273.15 K) and 1 atm pressure. At STP, 1 mole of any gas occupies a volume of 22.4 liters or 22,400 mL. This means if a gas sample is at STP, its volume can be directly related to the mole number.

Calculate Moles Displaced

Given that the organic substance displaced 56 mL of air under STP conditions, we can relate this to moles using the molar volume at STP:\[\text{Moles of gas} = \frac{\text{Volume of gas at STP (mL)}}{22,400 \, \text{mL/mol}} = \frac{56}{22,400}\]

Simplify the Moles Equation

Compute the moles calculation from Step 2:\[\text{Moles of gas} = \frac{56}{22,400} \approx 0.0025 \, \text{mol}\]

Apply Victor Meyer's Formula for Molecular Weight

According to Victor Meyer's method, the molecular weight (M.W.) of the compound is calculated as:\[\text{M.W.} = \frac{\text{mass of substance (g)}}{\text{moles of gas (mol)}}\]Substitute the given mass and calculated moles:\[\text{M.W.} = \frac{0.2}{0.0025} = 80 \, \text{g/mol}\]

Identify the Correct Choice

From the result in Step 4, the molecular weight is calculated to be 80 g/mol, which corresponds to option (c) in the provided choices.

Key concepts

Molecular Weight Calculation

Understanding how to calculate the molecular weight of a compound is crucial in chemistry. Molecular weight can be defined as the sum of the atomic weights of all atoms in a molecule. It is typically expressed in grams per mole (g/mol).
For instance, using Victor Meyer's method, you can determine the molecular weight of a compound by using the formula:

• \[ \text{Molecular Weight (M.W.)} = \frac{\text{mass of substance (g)}}{\text{moles of gas (mol)}} \]

In this method, the process involves displacing air with a known mass of the organic compound and measuring how much air is displaced. Then, using the molar volume concept at standard temperature and pressure (STP), the number of moles of the gas displaced can be ascertained. Consequently, this value is used along with the measured mass to determine the molecular weight.
Accurately determining molecular weight helps in identifying the compound and understanding its stoichiometric relationships.

Standard Temperature and Pressure (STP)

Standard Temperature and Pressure (STP) is a reference point used in chemistry to provide a standard for reporting gas volumes. The conditions defined for STP are:

• Temperature: 0°C or 273.15 K
• Pressure: 1 atmosphere (atm)

At these conditions, gases have predictable behaviors, which allows chemists to rely on fixed values like the molar volume of a gas.
The reason why these conditions are set is that they simplify calculations and comparisons between different gas behaviors under consistent metrics. It's also worth noting that while STP is useful, real-world conditions can deviate from these standard settings, so adjustments may be required for precise experimental results.

Molar Volume

Molar volume refers to the space that one mole of a substance occupies. Under the conditions of STP, the molar volume of an ideal gas is 22.4 liters or 22,400 mL per mole. This concept is invaluable because it allows chemists to relate the amount of substance to its volume without needing complex calculations.

• At STP, 1 mole gas = 22.4 liters (or 22,400 mL)

In practice, this means that if we know the volume of a gas, we can easily calculate the number of moles it contains by dividing the volume by 22.4 liters (or 22,400 mL). For example, if 56 mL of gas is displaced, it translates to approximately 0.0025 moles using the formula:

• \[ \text{Moles} = \frac{\text{Volume at STP (in mL)}}{22,400 \text{ mL/mol}} \]

Utilizing molar volume simplifies experimental predictions and aids in balancing chemical equations.

Organic Chemistry

Organic chemistry is the branch of chemistry dealing with carbon-containing compounds. These compounds primarily include hydrocarbons and their derivatives. Carbon's ability to form stable bonds with many elements, including itself, results in a vast array of organic molecules. Organic chemistry is key to understanding biological processes, synthesizing new materials, and developing pharmaceuticals. It's a versatile field that has applications in health, materials science, and environmental chemistry. Organic compounds are characterized by particular structures and reactivity. Knowing the molecular weight of these compounds is vital in understanding their properties and potential reactions. Techniques like Victor Meyer's method enable chemists to ascertain important parameters, influencing how these substances are utilized in various applications. Mastery of organic chemistry involves understanding both the formation and breakdown of these complex molecules, contributing significantly to advancements in technology and medicine.