What is the Avogadro number and how do you calculate vapor density?

Here are the solutions to your chemistry questions:

1. The number of atoms in one mole of a substance is equal to the Avogadro number.
The Avogadro number is approximately $6.022 \times 10^{23}$ particles per mole.

The correct option is (B) Avogadro number.

2. To find the substance with the highest vapor density, we need to calculate the molar mass of each compound, as vapor density is half the molar mass. The higher the molar mass, the higher the vapor density.

Given atomic masses: $\text{C}=12$, $\text{O}=16$, $\text{Cl}=35.5$, $\text{H}=1$.

• A) Ethanoic acid ($\text{CH}_3\text{COOH}$): Molar mass $= (2 \times 12) + (4 \times 1) + (2 \times 16) = 24 + 4 + 32 = 60 \text{ g/mol}$ Vapor density $= \frac{60}{2} = 30$

• B) Propanal ($\text{CH}_3\text{CH}_2\text{CHO}$): Molar mass $= (3 \times 12) + (6 \times 1) + (1 \times 16) = 36 + 6 + 16 = 58 \text{ g/mol}$ Vapor density $= \frac{58}{2} = 29$

• C) Dichloromethane ($\text{CH}_2\text{Cl}_2$): Molar mass $= (1 \times 12) + (2 \times 1) + (2 \times 35.5) = 12 + 2 + 71 = 85 \text{ g/mol}$ Vapor density $= \frac{85}{2} = 42.5$

• D) Ethanol ($\text{CH}_3\text{CH}_2\text{OH}$): Molar mass $= (2 \times 12) + (6 \times 1) + (1 \times 16) = 24 + 6 + 16 = 46 \text{ g/mol}$ Vapor density $= \frac{46}{2} = 23$

Comparing the vapor densities: $30, 29, 42.5, 23$. Dichloromethane has the highest vapor density.

The correct option is (C) Dichloromethane.

3. This problem uses Graham's Law of Diffusion, which states that the rate of diffusion of a gas is inversely proportional to the square root of its molar mass.

$$\frac{R_1}{R_2} = \sqrt{\frac{M_2}{M_1}}$$

Where $R = \frac{\text{Volume}}{\text{Time}}$.