To solve this problem, we will use Raoult's Law for ideal solutions. We need the pure vapor pressures of Benzene and Methylbenzene (Toluene).
Assumptions:
- The solution is ideal.
- The temperature is constant, typically 25°C.
- Pure vapor pressure of Benzene (PB0) = 95.1 mmHg
- Pure vapor pressure of Methylbenzene (Toluene) (PM0) = 28.4 mmHg
The mole fractions of Benzene (XB) are given as: 0, 0.25, 0.5, 0.75, and 1.
a. Find the respective mole fraction of methylbenzene at this concentration.
The sum of mole fractions in a binary solution is 1: XB+XM=1.
So, XM=1−XB.
- For XB=0: XM=1−0=1
- For XB=0.25: XM=1−0.25=0.75
- For XB=0.5: XM=1−0.5=0.5
- For XB=0.75: XM=1−0.75=0.25
- For XB=1: XM=1−1=0
bi. Calculate the respective vapour pressure contributions of benzene at these concentration.
According to Raoult's Law, the partial vapor pressure of Benzene (PB) is given by PB=XB⋅PB0.
- For XB=0: PB=0×95.1mmHg=0 mmHg
- For XB=0.25: PB=0.25×95.1mmHg=23.78 mmHg
- For XB=0.5: PB=0.5×95.1mmHg=47.55 mmHg
- For XB=0.75: PB=0.75×95.1mmHg=71.33 mmHg
- For XB=1: PB=1×95.1mmHg=95.1 mmHg
bii. Calculate the respective vapour pressure contributions for methylbenzene at these concentration.
According to Raoult's Law, the partial vapor pressure of Methylbenzene (PM) is given by PM=XM⋅PM0.
- For XM=1 (when XB=0): PM=1×28.4mmHg=28.4 mmHg
- For XM=0.75 (when XB=0.25): PM=0.75×28.4mmHg=21.3 mmHg
- For XM=0.5 (when XB=0.5): PM=0.5×28.4mmHg=14.2 mmHg
- For XM=0.25 (when XB=0.75): PM=0.25×28.4mmHg=7.1 mmHg
- For XM=0 (when XB=1): PM=0×28.4mmHg=0 mmHg
c. Calculate the total Vapour pressures at the Various concentration.
According to Dalton's Law of Partial Pressures, the total vapor pressure (Ptotal) is the sum of the partial vapor pressures: Ptotal=PB+PM.
- For XB=0: Ptotal=0mmHg+28.4mmHg=28.4 mmHg
- For XB=0.25: Ptotal=23.78mmHg+21.3mmHg=45.08 mmHg
- For XB=0.5: Ptotal=47.55mmHg+14.2mmHg=61.75 mmHg
- For XB=0.75: Ptotal=71.33mmHg+7.1mmHg=78.43 mmHg
- For XB=1: Ptotal=95.1mmHg+0mmHg=95.1 mmHg
Summary Table for Plotting (d):
| XB | XM | PB (mmHg) | PM (mmHg) | Ptotal (mmHg) |
| :---- | :---- | :----------- | :----------- | :----------------- |
| 0 | 1 | 0 | 28.4 | 28.4 |
| 0.25 | 0.75 | 23.78 | 21.3 | 45.08 |
| 0.5 | 0.5 | 47.55 | 14.2