1. A solution contains 25% water, 25% ethanol and 50% acetic acid by mass. Calculate the mole fraction of each component.
2. Which of 1 molar and 1 molal solution is more concentrated and why?
3. Why a bottle containing liquid ammonia is first cooled in ice before opening it ?
4. The vapour pressure of two volatile liquids A and B at 313 K are 160 mm Hg and 60 mm Hg respectively. Calculate the partial vapour pressure of each component and the total vapour pressure of the solution obtained by mixing 1 mole of A with 4 mole of B at 313 K. Assume the solution to be ideal in behaviour.
5. Give difference between ideal and non- ideal solution.
6. Give difference between diffusion and osmosis.
7. What is exoosmosis and endoosmosis ?
8. In the measurements of osmotic pressure, a method which avoids the entry of the solvent into solution is preferred. Why?
9. Carbon Tetrachloride and water are immiscible where ethyl alcohol and water are miscible in all proportions. Co-relate this behaviour with molecular structure of three compounds.
10. Define molal elevation constant and molal depression constant.
Solutions:-
Ans1:- Suppose the total mass of the solution = 100g
Mass of water = 25 g
Mass of ethanol = 50 g
Mass of acetic acid = 50 g
So, the number of moles of water = 25/18 = 1.38 moles
Number of moles of ethanol = 25/46 = 0.54 moles
Number of moles of acetic acid = 50/60 = 0.83 moles
Total no. of moles in solution = 1.38+0.54+0.83 = 2.75 moles
So, molefraction of water = no. of moles of water / total no. of moles
=> 1.38/2.75 = 0.502
Similarly, molefraction of ethanol = 0.54/2.75 = 0.196
And, molefraction of acetic acid = 0.83/2.75 = 0.302
Ans2:- In aqueous Solution, 1M solution has higher concentration than that of 1 m solution. This is because in 1 molal solution, 1 mole of solute is dissolved in 1 kg water while 1 molar solution, 1 mole of solute is dissolved in less than 1000g of water. But in case of non- aqueous solution, 1 m solution can have concentration greater or less than 1 M solution depending upon the density of the solution.
Ans3:- The vapour pressure of ammonia is very high at room temperature. On cooling, its vapour pressure decreases and therefore, liquid ammonia will not splash out on opening the bottle.
Ans4:- According to given data in question,
Vapour pressure of pure A = 160 mm
Vapour pressure of pure B =60 mm
No. of moles of A = 1 mole
No. of moles of B = 4 mole
So, Molefraction of A = 1/5 =0.2
Molefraction of B = 4/5 = 0.8
So, partial pressure of A = molefraction of A × vapour pressure of pureA
=> 0.2 × 160 = 32 mm
Partial pressure of pure B = molefraction of B × vapour pressure of pure B
=> 0.8 × 60 = 48 mm
Lastly, total vapour pressure of the solution = 32 + 48 = 80 mm
Ans5:- Ideal solution:- i) In ideal solution, the components have similar interaction as were in pure components.
ii) There is no volume change on mixing.
iii) There is no enthalpy change on mixing.
iv) Each component obey Raoult's law at all temperature and concentration.
Non-ideal solution:- i) In non-ideal, the components have different interaction than those of pure components.
ii) There is change in volume takes place on mixing.
iii) There is change in enthalpy takes place on mixing.
iv) Each component doesn't obey Raoult's law and show either positive or negative deviation.
Ans6:- Diffusion:- i) It takes place directly and no semipermeable membrane is needed.
ii) In diffusion the molecules move from a region of higher concentration into a region of lower Concentration.
iii)In diffusion, the solvent as well as the solute molecules move directly into each other.
iv) It takes place in gases as well.
v) It is a slow process.
Osmosis:- i) It needs a semipermeable membrane.
ii) In osmosis, the molecules move from a region of lower Concentration into a region of higher concentration.
iii) In osmosis, only the solvent molecule flow through semipermeable membrane.
iv) It is limited only to the solutions.
v) It is fast process.
Ans7:- Exoosmosis is the process when water flows out of a cell and inflow of water in the cell is called Endoosmosis.
Ans8:- If the solvent enters the solution, the concentration of solution changes and so the osmotic pressure.
Ans9:- The misciblity of ethyl alcohol with water is due to hydrogen bonding while no such phenomenon occurs between carbon tetrachloride and water and, therefore, carbon tetrachloride and water are immiscible in all proportions.
Ans10:- Molal elevation constant or ebullioscopic constant is defined as the elevation in boiling point when 1 mole of a solute is dissolved in 1000g of the solvent.
Molal depression constant or Molal cryoscopic constant is defined as the depression in freezing point when one mole of the solute is dissolved in 1000g of the solvent.