Examples:

1) The osmotic pressure of a solution of 1.37 g of a substance in [tex]100 \, \text{cm}^3[/tex] of water is 1.779 atm at [tex]17^{\circ} \text{C}[/tex]. Calculate the relative molecular mass of the substance.

Given:
- 1 atm = [tex]1.013 \times 10^5 \, \text{N/m}^2[/tex]
- [tex]R = 8.31 \, \text{J K}^{-1} \text{mol}^{-1}[/tex]



Answer :

Alright, let's break this problem down step-by-step to understand and solve it.

### Given Data:
1. Osmotic Pressure ([tex]\(\Pi\)[/tex]) = 1.779 atm
2. Mass of Solute (m) = 1.37 grams
3. Volume of Solution (V) = 100 cm[tex]\(^3\)[/tex] = 0.1 liters (since 1 liter = 1000 cm[tex]\(^3\)[/tex])
4. Temperature (T) = 17°C = 290.15 K (we convert from Celsius to Kelvin by adding 273.15)
5. Universal Gas Constant (R) = 0.0821 L atm K[tex]\(^{-1}\)[/tex] mol[tex]\(^{-1}\)[/tex]

### Steps to Find the Molar Mass:

1. Convert Osmotic Pressure to Required Units:
[tex]\[ \Pi = 1.779 \text{ atm} \][/tex]

2. Convert Volume to Liters (already given as 0.1 liters):
[tex]\[ V = 0.1 \, \text{L} \][/tex]

3. Convert Temperature to Kelvin (already given conversion):
[tex]\[ T = 290.15 \, \text{K} \][/tex]

4. Calculate the Number of Moles of Solute ([tex]\(n\)[/tex]) using the osmotic pressure formula:

The osmotic pressure formula is given by:
[tex]\[ \Pi = \frac{nRT}{V} \][/tex]

Rearranging to solve for [tex]\(n\)[/tex] (number of moles):
[tex]\[ n = \frac{\Pi \cdot V}{R \cdot T} \][/tex]

Substituting the given values:
[tex]\[ n = \frac{1.779 \, \text{atm} \times 0.1 \, \text{L}}{0.0821 \, \text{L atm K}^{-1} \times 290.15 \, \text{K}} \][/tex]

From the given calculation, we know the number of moles:
[tex]\[ n = 0.0074681015720584705 \, \text{moles} \][/tex]

5. Calculate the Molar Mass (M):

The molar mass (M) can be found using the formula:
[tex]\[ M = \frac{m}{n} \][/tex]

Where [tex]\(m\)[/tex] is the mass of the solute in grams and [tex]\(n\)[/tex] is the number of moles calculated above.
Substituting the values:
[tex]\[ M = \frac{1.37 \, \text{g}}{0.0074681015720584705 \, \text{moles}} \][/tex]

From the given result, we know the molar mass:
[tex]\[ M = 183.44688898257448 \, \text{g/mol} \][/tex]

### Conclusion:

The relative molecular mass of the solute, given the osmotic pressure conditions, is approximately [tex]\(183.45 \, \text{g/mol}\)[/tex].

This step-by-step solution provides a detailed and comprehensive method for calculating the molar mass of the solute using the provided data and formulas.