Advertisements
Advertisements
Question
Benzene and toluene form ideal solution over the entire range of composition. The vapour pressure of pure benzene and toluene at 300 K are 50.71 mm Hg and 32.06 mm Hg respectively. Calculate the mole fraction of benzene in vapour phase if 80 g of benzene is mixed with 100 g of toluene.
Advertisements
Solution
Given: Vapour pressure of pure benzene `(p_b^0)` = 50.71 mm Hg
Vapour pressure of pure toluene `(p_t^0)` = 32.06 mm Hg
Molar mass of benzene (C6H6) = 6 × 12 + 6 × 1
= 78 g mol−1
Molar mass of toluene (C6H5CH3) = 7 × 12 + 8 × 1
= 92 g mol−1
Number of moles present in 80 g of benzene = `80/78` mol
= 1.026 mol
Number of moles present in 100 g of toluene = `100/92` mol
= 1.087 mol
Mole fraction of benzene (χb) = `(1.026)/(1.026 + 1.087)`
= 0.486
Mole fraction of toluene (χ) = 1 − 0.486
= 0.514
Partial vapour pressure of benzene (pb) = `chi_b xx p_b^0`
= 0.486 × 50.71
= 24.65 mm Hg
Partial vapour pressure of toluene (pt) = `chi_t xx p_t^0`
= 0.514 × 32.06
= 16.48 mm Hg
As a result, the mole fraction of benzene in the vapour phase is as follows:
`p_b/(p_b + p_t)`
= `24.65/(24.65 + 16.48)`
= `24.65/41.13`
= 0.599
= 0.6
RELATED QUESTIONS
Why does a solution containing non-volatile solute have higher boiling point than the pure solvent ?
What type of deviation is shown by a mixture of ethanol and acetone? Give reason.
An aqueous solution of 2% non-volatile solute exerts a pressure of 1.004 bar at the normal boiling point of the solvent. What is the molar mass of the solute?
The vapour pressure of water is 12.3 kPa at 300 K. Calculate vapour pressure of 1 molal solution of a non-volatile solute in it.
Calculate the mass of a non-volatile solute (molar mass 40 g mol−1) which should be dissolved in 114 g octane to reduce its vapour pressure to 80%.
A solution containing 30 g of non-volatile solute exactly in 90 g of water has a vapour pressure of 2.8 kPa at 298 K. Further, 18 g of water is then added to the solution and the new vapour pressure becomes 2.9 kPa at 298 K. Calculate:
- molar mass of the solute.
- vapour pressure of water at 298 K.
100 g of liquid A (molar mass 140 g mol−1) was dissolved in 1000 g of liquid B (molar mass 180 g mol−1). The vapour pressure of pure liquid B was found to be 500 torr. Calculate the vapour pressure of pure liquid A and its vapour pressure in the solution if the total vapour pressure of the solution is 475 Torr.
For the reaction :
\[\ce{2NO_{(g)} ⇌ N2_{(g)} + O2_{(g)}}\];
ΔH = -heat
Kc = 2.5 × 102 at 298K
What will happen to the concentration of N2 if :
(1) Temperature is decreased to 273 K.
(2) The pressure is reduced
Match the following:
| (i) | Colligative property | (a) | Polysaccharide |
| (ii) | Nicol prism | (b) | Osmotic pressure |
| (iii) | Activation energy | (c) | Aldol condensation |
| (iv) | Starch | (d) | Polarimeter |
| (v) | Acetaldehyde | (e) | Arrhenius equation |
What will be the vapour pressure of a solution containing 5 moles of sucrose (C12H22O11) in 1 kg of water, if the vapour pressure of pure water is 4.57 mm of Hg? [C = 12, H = 1, O = 16]
Raoult’s law states that for a solution of volatile liquids the partial pressure of each component in the solution is ____________.
The boiling point of an azeotropic mixture of water and ethanol is less than that of water and ethanol. The mixture shows ____________.
Using Raoult’s law explain how the total vapour pressure over the solution is related to mole fraction of components in the following solutions.
\[\ce{CHCl3(l) and CH2Cl2(l)}\]
Two liquids X and Y form an ideal solution. The mixture has a vapour pressure of 400 mm at 300 K when mixed in the molar ratio of 1 : 1 and a vapour pressure of 350 mm when mixed in the molar ratio of 1 : 2 at the same temperature. The vapour pressures of the two pure liquids X and Y respectively are ______.
If the weight of the non-volatile solute urea (NH2–CO–NH2) is to be dissolved in 100 g of water, in order to decrease the vapour-pressure of water by 25%, then the weight of the solute will be ______ g.
The vapour pressure of pure liquid X and pure liquid Y at 25°C are 120 mm Hg and 160 mm Hg respectively. If equal moles of X and Y are mixed to form an ideal solution, calculate the vapour pressure of the solution.
An azeotropic mixture of two liquids will have a boiling point lower than either of the two liquids when it ______.
