Why is it not possible to obtain pure ethanol by fractional distillation? What general name is given to binary mixtures which show deviation from Raoult's law and whose components cannot be separated by fractional distillation. How many types of such mixtures are there?
The solution or mixture having same composition in liquid as well as in vapour phase and boils at a constant temperature is known as azeotropes. Due to constant composition it can't be separated by fractional distillation. There are two types of azeotropes
(i) Minimum boiling azeotropes Solutions which show large positive deviation from Raoult's law form minimum boiling azeotropes at a specific composition. e.g., ethanol -water mixture
(ii) Maximum boiling azeotropes Solutions which show large negative deviation from Raoult's law form maximum boiling azeotropes. e.g., solution having composition 68$\%$ $\mathrm{HNO}_3$ and $32 \%$ water by mass.
When kept in water, raisin swells in size. Name and explain the phenomenon involved with the help of a diagram. Give three applications of the phenomenon.
This phenomenon is called endo osmosis, i.e., movement of water inside the raisin and shown with the help of diagram as
The process of osmosis is of immense biological as well as industrial important. It is evident from the following examples.
(i) Movement of water from soil into plant roots and subsequently into upper portion of the plant is partly due to osmosis.
(ii) Preservation of meat against bacterial action by addition of salt.
(iii) Preservation of fruits against bacterial action by adding sugar. Bacterium in canned fruit loses water through the process of osmosis and become inactive.
(iv) Reverse-osmosis is used in desalination of water.
Discuss biological and industrial applications of osmosis.
(i) In animals, water moves into different parts of the body under the effect of the process of osmosis.
(ii) Stretching of leaves, flower, etc., is also controlled by osmosis.
(iii) Osmosis helps in rapid growth of the plants and germination of seeds.
(iv) Different movements of plants such as opening and closing of flowers etc, are controlled by osmosis.
How can you remove the hard calcium carbonate layer of the egg without damaging its semipermeable membrane? Can this egg be inserted into a bottle with a narrow neck without distorting its shape? Explain the process involved.
When egg is placed in mineral acid solution outershell of egg dissolves. Egg is now removed and placed in hypertonic solution. Size of egg get reduced and egg shrivels due to osmosis. Egg is now placed in a bottle with narrow neck. Finally on adding hypotonic solution egg regain its shape due to osmosis.
Diagramatically it can be represented as
Why is the mass determined by measuring a colligative property in case of some solutes abnormal? Discuss it with the help of van't Hoff factor.
Certain compounds when dissolved in suitable solvents either dissociate or associate. e.g., ethanoic acid dimerises in benzene due to H -bonding, while in water, it dissociates and forms ions.
As a result the number of chemical species in solution increases or decreases as compared to the number of chemical species of solute added to form the solution.
Since, the magnitude of colligative property depends on the number of solute particles, it is expected that the molar mass determined on the basis of colligative properties will either higher or lower than the expected value or the normal value and is called abnormal molar mass.
In order to account for the extent of dissociation or association of molecules in solution, van't Hoff introduced a factor, $i$, known as the van't Hoff factor.
$$\begin{aligned} & i= \frac{\text { expected molar mass }}{\text { abnormal molar mass }}=\frac{\text { observed colligative property }}{\text { calculated colligative property }} \\ & \\ &=\frac{\text {total number of moles of particles after association or dissociation}}{\text { total number of moles of particles before association or dissociation}} \\ & \end{aligned}$$