Question 12 Marks
0.05 moles of ethanoic acid is dissolved in $2 5 0 ~ g m$ benzene. Calculate molality of solution.
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Question 22 Marks
Calculate the mole fraction of gas $A$ is the soltuion made an mixing 0.5 moles of gas $A$ and 4.5 moles of gas B.
View full question & answer→Question 32 Marks
Define osmosis. Write the name of the method used in desalination of sea-water.
Answer
View full question & answer→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.
Question 42 Marks
1.25 g of protein is present in 300 mL aqueous solution of a protein. The osmotic pressure of this solution at 300 K was found to be $2.50 \times 10^{-3}$ bar. Calculate the molar mass of protein. $[R=0.083 L$ bar $\operatorname{mol}^{-1} K^{-1}$ ].
View full question & answer→Question 52 Marks
(i) What are anti-freezing agents?
(ii) What is called de-icing agent?
(ii) What is called de-icing agent?
Answer
View full question & answer→(i) The substance which when mixed with water reduces its freezing point is called anti-freezing.Example : Ethylene glycol
.(ii) The substance which reduces the freezing point of water and which when poured on ice melt it quickly, is called de-icing agent. For example : $NaCl , CaCl _2$ etc.
.(ii) The substance which reduces the freezing point of water and which when poured on ice melt it quickly, is called de-icing agent. For example : $NaCl , CaCl _2$ etc.
Question 62 Marks
For any solvent, the molal gradient constants value is certain. Why?
Answer
View full question & answer→The molal elevation constant is calculated from the following formula :
All the value present in this formula, R (gas constant or solution constant), $M _1$ (Molar mass of solvent, $T _{ b }$ (boiling point of solvent) and $\Delta_{\text {vaporisation }} H$ (enthalpy of vaporisation) of solvent are fixed, hence molar elevation constant $\left( K _{ b }\right)$ is also fixed.
All the value present in this formula, R (gas constant or solution constant), $M _1$ (Molar mass of solvent, $T _{ b }$ (boiling point of solvent) and $\Delta_{\text {vaporisation }} H$ (enthalpy of vaporisation) of solvent are fixed, hence molar elevation constant $\left( K _{ b }\right)$ is also fixed.
Question 72 Marks
Food cooks quickly in pressure cooker but slowly in mountains. Explain it.
Answer
View full question & answer→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.
Question 82 Marks
Why is it more important to take $CaCl_2$ instead of $NaCl$ to remove snow accumulated on roads?
Answer
View full question & answer→Both $NaCl$ and $CaCl _2$ acts as anti$-$freezing agents because mixing them reduces the freezing point of water. But freezing point depression is a particle number property which depends on the number of particles. By inonization of $CaCl _2$, ice melts more rapidly due to greater decrease in freezing point, the time of freezing of ice increases.
Question 92 Marks
Why does ethylene glycol is mixed with water to be used in car radiator during winter season?
Answer
View full question & answer→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.
Question 102 Marks
The molar mass of a volatile substance cannot be determined from boiling point elevation. Why?
Answer
View full question & answer→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.
Question 112 Marks
The melting point and boiling point of a substance provides a very information about impurities present in a substance. Explain this statement.
Answer
View full question & answer→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.
Question 122 Marks
When fresh grapes are kept in concentrated salt solution they shrink, whereas when they are kept back in water they swell up. Why?
Answer
View full question & answer→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.
Question 132 Marks
Explain the limitations of Raoult's law.
Answer
View full question & answer→(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.
(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.
Question 142 Marks
The mixture of ethyl alcohol and cyclohexane shows positive deviation from Raoult's law. Why?
Answer
View full question & answer→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.