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The vapour pressure of benzene at a certain temp. is 640 mm Hg. A non-volatile-non-electrolyte and weighing 2.175g is added to 39.0g of benzene. The vapour pressure of the solution is 600 mm Hg. What is the molecular weight of the solid substance ?
- a)6.96
- b)65.3
- c)63.8
- d)none of the above
Correct answer is option 'B'. Can you explain this answer?
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The vapour pressure of benzene at a certain temp. is 640 mm Hg. A non-...
Given:
- Vapour pressure of benzene (solvent) = 640 mm Hg
- Vapour pressure of solution = 600 mm Hg
- Mass of non-volatile-non-electrolyte (solute) = 2.175 g
- Mass of benzene (solvent) = 39.0 g
To find: Molecular weight of the solid substance (solute)
Key concept:
According to Raoult's Law, the vapor pressure of a solution is directly proportional to the mole fraction of the solvent. Mathematically, it can be represented as:
P solution = X solvent * P solvent
Where:
P solution = Vapor pressure of the solution
X solvent = Mole fraction of the solvent
P solvent = Vapor pressure of the pure solvent
Solution:
Step 1: Calculate the mole fraction of the solvent (benzene).
Mole fraction of benzene (X benzene) = Moles of benzene / Total moles of solution
To find the moles of benzene, we need to convert its mass to moles using its molar mass.
Molar mass of benzene (C6H6) = (12.01 * 6) + (1.01 * 6) = 78.11 g/mol
Moles of benzene = Mass of benzene / Molar mass of benzene
= 39.0 g / 78.11 g/mol
Step 2: Calculate the mole fraction of the solute.
As the solute is non-volatile, its vapor pressure is negligible. Therefore, the mole fraction of the solute (X solute) is zero.
Step 3: Calculate the total moles of the solution.
Total moles of the solution = Moles of benzene + Moles of solute
= Moles of benzene + 0 (as X solute = 0)
Step 4: Calculate the mole fraction of the solvent.
X benzene = Moles of benzene / Total moles of the solution
Step 5: Apply Raoult's Law to calculate the vapor pressure of the solution.
P solution = X benzene * P benzene
Given:
P solution = 600 mm Hg
P benzene = 640 mm Hg
Substituting the values in the equation:
600 mm Hg = X benzene * 640 mm Hg
Step 6: Calculate the molecular weight of the solid substance (solute).
Now, we know the mole fraction of benzene, we can find the mole fraction of the solute using the equation:
X solute = 1 - X benzene
Mole fraction of solute = X solute
To find the moles of solute, we need to convert its mass to moles using its molar mass.
Moles of solute = Mass of solute / Molar mass of solute
= 2.175 g / (Molar mass of solute)
The molecular weight of the solid substance (solute) can be calculated using the equation:
Molar mass of solute = Mass of solute / Moles of solute
Substituting the values,
- Vapour pressure of benzene (solvent) = 640 mm Hg
- Vapour pressure of solution = 600 mm Hg
- Mass of non-volatile-non-electrolyte (solute) = 2.175 g
- Mass of benzene (solvent) = 39.0 g
To find: Molecular weight of the solid substance (solute)
Key concept:
According to Raoult's Law, the vapor pressure of a solution is directly proportional to the mole fraction of the solvent. Mathematically, it can be represented as:
P solution = X solvent * P solvent
Where:
P solution = Vapor pressure of the solution
X solvent = Mole fraction of the solvent
P solvent = Vapor pressure of the pure solvent
Solution:
Step 1: Calculate the mole fraction of the solvent (benzene).
Mole fraction of benzene (X benzene) = Moles of benzene / Total moles of solution
To find the moles of benzene, we need to convert its mass to moles using its molar mass.
Molar mass of benzene (C6H6) = (12.01 * 6) + (1.01 * 6) = 78.11 g/mol
Moles of benzene = Mass of benzene / Molar mass of benzene
= 39.0 g / 78.11 g/mol
Step 2: Calculate the mole fraction of the solute.
As the solute is non-volatile, its vapor pressure is negligible. Therefore, the mole fraction of the solute (X solute) is zero.
Step 3: Calculate the total moles of the solution.
Total moles of the solution = Moles of benzene + Moles of solute
= Moles of benzene + 0 (as X solute = 0)
Step 4: Calculate the mole fraction of the solvent.
X benzene = Moles of benzene / Total moles of the solution
Step 5: Apply Raoult's Law to calculate the vapor pressure of the solution.
P solution = X benzene * P benzene
Given:
P solution = 600 mm Hg
P benzene = 640 mm Hg
Substituting the values in the equation:
600 mm Hg = X benzene * 640 mm Hg
Step 6: Calculate the molecular weight of the solid substance (solute).
Now, we know the mole fraction of benzene, we can find the mole fraction of the solute using the equation:
X solute = 1 - X benzene
Mole fraction of solute = X solute
To find the moles of solute, we need to convert its mass to moles using its molar mass.
Moles of solute = Mass of solute / Molar mass of solute
= 2.175 g / (Molar mass of solute)
The molecular weight of the solid substance (solute) can be calculated using the equation:
Molar mass of solute = Mass of solute / Moles of solute
Substituting the values,
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The vapour pressure of benzene at a certain temp. is 640 mm Hg. A non-...
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The vapour pressure of benzene at a certain temp. is 640 mm Hg. A non-volatile-non-electrolyte and weighing 2.175g is added to 39.0g of benzene. The vapour pressure of the solution is 600 mm Hg. What is the molecular weight of the solid substance ?a)6.96b)65.3c)63.8d)none of the aboveCorrect answer is option 'B'. Can you explain this answer?
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The vapour pressure of benzene at a certain temp. is 640 mm Hg. A non-volatile-non-electrolyte and weighing 2.175g is added to 39.0g of benzene. The vapour pressure of the solution is 600 mm Hg. What is the molecular weight of the solid substance ?a)6.96b)65.3c)63.8d)none of the aboveCorrect answer is option 'B'. Can you explain this answer? for NEET 2024 is part of NEET preparation. The Question and answers have been prepared according to the NEET exam syllabus. Information about The vapour pressure of benzene at a certain temp. is 640 mm Hg. A non-volatile-non-electrolyte and weighing 2.175g is added to 39.0g of benzene. The vapour pressure of the solution is 600 mm Hg. What is the molecular weight of the solid substance ?a)6.96b)65.3c)63.8d)none of the aboveCorrect answer is option 'B'. Can you explain this answer? covers all topics & solutions for NEET 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for The vapour pressure of benzene at a certain temp. is 640 mm Hg. A non-volatile-non-electrolyte and weighing 2.175g is added to 39.0g of benzene. The vapour pressure of the solution is 600 mm Hg. What is the molecular weight of the solid substance ?a)6.96b)65.3c)63.8d)none of the aboveCorrect answer is option 'B'. Can you explain this answer?.
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