Advertisements
Advertisements
Question
Heptane and octane form an ideal solution. At 373 K, the vapour pressures of the two liquid components are 105.2 kPa and 46.8 kPa respectively. What will be the vapour pressure of a mixture of 26.0 g of heptane and 35 g of octane?
Advertisements
Solution 1
Vapour pressure of heptane `(p_1^circ)` = 105.2 kPa
Vapour pressure of octane `(p_2^circ)` = 46.8 kPa
We know that,
Molar mass of heptane (C7H16) = 7 × 12 + 16 × 1
= 100 g mol−1
∴ Number of moles of heptane = `26/100` mol
= 0.26 mol
Molar mass of octane (C8H18) = 8 × 12 + 18 × 1
= 114 g mol−1
∴ Number of moles of octane = `35/114` mol
= 0.31 mol
Mole fraction of heptane (x1) = `0.26/(0.26 + 0.31)`
= 0.456
And, mole fraction of octane (x2) = 1 − 0.456
= 0.544
Now, partial pressure of heptane (p1) = `x_1 p_1^circ`
= 0.456 × 105.2
= 47.97 kPa
Partial pressure of octane (p2) = `x_2 p_2^circ`
= 0.544 × 46.8
= 25.46 kPa
Hence, the vapour pressure of the solution (ptotal) = p1 + p2
= 47.97 + 25.46
= 73.43 kPa
Solution 2
Vapour pressure of heptane `(p_1^circ)` = 105.2 kPa
Vapour pressure of octane `(p_2^circ)` = 46.8 kPa
No. of moles of heptane = `26/100` ..(Mol. mass of heptane = 100 g mol−1)
= 0.260
No. of moles of octane = `35/114` ...(Mol. mass of octane = 114 g mol−1)
= 0.307
∴ Total no. of moles in solution = 0.260 + 0.307
= 0.567
Hence, mole fraction of heptane = `0.260/0.567`
= 0.458
Mole fraction of octane = `0.307/0.567`
= 0.541
Since the solution is ideal,
p = `p_"heptane" + p_"octane"`
= (0.458 × 105.2) + (0.541 × 46.8) kpa
= 48.1816 + 25.3188
= 73.50 kpa
RELATED QUESTIONS
Vapour pressure of pure acetone and chloroform at 328 K are 741.8 mm Hg and 632.8 mm Hg respectively. Assuming that they form ideal solution over the entire range of composition, plot Ptotal, `P_"chloroform"` and `P_"acetone"` as a function of `chi_"acetone"`. The experimental data observed for different compositions of mixtures is:
| `bb(100 xx chi_"acetone")` | `bb(P_"acetone"//"mm Hg")` | `bb(P_"chloroform"//"mm Hg")` |
| 0 | 0 | 632.8 |
| 11.8 | 54.9 | 548.1 |
| 23.4 | 110.1 | 469.4 |
| 36.0 | 202.4 | 359.7 |
| 50.8 | 322.7 | 257.7 |
| 58.2 | 405.9 | 193.6 |
| 64.5 | 454.1 | 161.2 |
| 72.1 | 521.1 | 120.7 |
Plot this data also on the same graph paper. Indicate whether it has a positive or negative deviation from the ideal solution.
Fill in the blanks by choosing the appropriate word/words from those given in the brackets:
Ideal solutions obey ………. law and they …………. form azeotropic mixtures.
(Henry’s, aldol condensation, absence, do not, ohm, Raoult’s, increases, common ion effect, easily, three, solubility product, ohm-1, two, four, ohm-1, cm2, Cannizzaro, ohm-1 cm-1, zero, decreases, presence)
Which of the following concentration terms is/are independent of temperature
Two liquids X and Y on mixing gives a warm solution. The solution is ______.
The mass of a non – volatile solute (molar mass 80 g mol-1) should be dissolved in 92g of toluene to reduce its vapour pressure to 90% ______.
For ideal solution the volume of mixing of the pure components to form the solution is ____________.
The rate at which a solid dissolves in liquid does not depend on ____________.
Which of the following condition is not satisfied by an ideal solution?
If two liquids A and B form minimum boiling azeotrope at some specific composition then ______.
Concentration terms such as mass percentage, ppm, mole fraction and molality are independent of temperature, however molarity is a function of temperature. Explain.
What is “semi permeable membrane”?
Assertion: When a solution is separated from the pure solvent by a semipermeable membrane, the solvent molecules pass through it from pure solvent side to the solution side.
Reason: Diffusion of solvent occurs from a region of high concentration solution to a region of low concentration solution.
Explain the terms ideal and non-ideal solutions in the light of forces of interactions operating between molecules in liquid solutions.
How many times more hydrogen ions in a solution with a pH of 3 than in a solution with a pH of 6
On increase in pressure for dissociation ofN2O4 into NO2, equilibrium shift towards
Assertion (A): The enthalpy of mixing Δmix H is equal to zero for an ideal solution.
Reason (R): For an ideal solution the interaction between solute and solvent molecules is stronger than the interactions between solute-solute or solvent-solvent molecules.
