Chemistry 2 Marks Questions

Osmosis: When a solvent and a solution formed by dissolving a solute in it are separated by a semi- permeable membrane, then in this situation, the spontaneous movement (flow) of the solvent towards the solution through the semi-permeable membrane is called osmosis or when two solutions of different concentration are sparated by a semipermeable membrane, then the spontaneous movement of solvent from lower concentration to higher concentration of solution is called osmosis. The method used to desaline the sea-water is reverse osmosis.

The boiling point of every liquid is fixed and on increasing the pressure, the boiling point increases, Due to high pressure in a pressure cooker, the boiling point of water increases, hence it boils at a higher temperature, due to which food receives more heat, hence cooked quickly whereas the atmospheric pressure is less on mountains, due to which boiling point also reduces. Therefore, food get boiled quickly but food receives less heat due to which it cooks slowly.

In winter season, water alone cannot be used to cool the car engine because water freezes at 0°C (273K) whereas the freezing point of 35% (V/V) aqueous solution of ethylene glycol is 17.6°C, hence it does not freeze even at low temperatures, hence, is used as a coolant. Here, ethylene glycol acts as an anti-freezing agent. That is the reason for which ethylene glycol is added in water to be used in car radiator in winter season.

Boiling point elevation methods are suitable for only non-volatile substances because when a volatile substance is added to a solution and heated, then the volatile substance comes out as a vapour due to which there will be no elevation in boiling point, hence molar mass of volatile substance cannot be determined by this method.

In pure state, the melting and boiling point of a substance is fixed. When non-volatile impurities are found in it, the boiling point increases and melting point decreases, as the amount of impurity increases, these values also change in the same proportion, hence information about the impurities present in a substance is obtained from melting and boiling point.

Due to post-osmosis, the solvent moves from the solution of lower concentration to a solution of higher concentration, the grapes cell membrane here acts as semipermeable membrane, when grapes are kept in concentrated solution of salt, water comes out of the grapes and they shrink and after putting them back in water, they swell up and becomes fresh again.

(i) This law applies only to dilute solutions.
(ii) This law does not get applied to the solution of electrolytes.
(iii) Raoult's law does not apply even when there is condensation or dissociation of substances in solution.

Van der Waals force is found between the molecules of cyclohexane and hydrogen bond is found between ethyl alcohol molecule (ethanol), but when ethanol and cyclohexane are mixed the hydrogen bond present between the molecules of ethanol are broken i.e. A-B attraction, is less than the A-A and B-B attraction, hence molecules moves farther apart and is an example of positive deviation.

Freezing point depression is a molecular property, ie, as the number of particles increases, the freezing point depression also increases. The sequence acetic acid (CH₃COOH), trichloroacetic acid (CCl₃COOH) and trifluoroacetic acid (CF₃COOH) is the increasing order of acidic properties, that is, they are in also increasing order of dissociation, hence the number of particles will increase. Therefore, the above sequence is the increasing sequence of depression in freezing point.

Water is a polar solvent in which hydrogen bond is found between molecules.
(a) (ii) Toluene and (v) chloroform are insoluble in water because these are covalent compounds, hence they do not form hydrogen bond with water.
(b) (i) Phenol and (vi) Pentanol are partially soluble in water because these compounds have polarity but their non-polar part is large, hence they form very weak hydrogen bond with water.
(c) (iii) Formic acid and (iv) Ethylene glycol are highly soluble in water in large doses because they form strong bonds of hydrogen with water.

On increasing the temperature, the solubility of gases in liquids decreases because when dissolved, the molecules of gases dissolve in the liquid phase and are present in it, hence it is similiar to condensation reaction and in this process, heat is emitted (exothermic process). Solubility of gases in liquid is in dynamic equilibrium hence according to Le Chatelier's law, as the temperature increases, the solubility will decrease, that is, the equilibrium will move in reverse direction.