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#### Questions and Answers

Chapter 2 Solutions

**Question 1.: Calculate the mass percentage of aspirin (C _{9}H_{8}O_{4}) in acetonitrile (CH_{3}CN) when 6.5 g of C_{9}H_{8}O_{4} is dissolved in 450 g of CH_{3}CN. **

**Question 2.: Calculate the percentage composition in terms of mass of a solution obtained by mixing 300 g of a 25 % and 400 g of a 40 % solution by mass. **

**Question 3.: Calculate the molality of a solution containing 20.7 g of K _{2}CO_{3} dissolved in 500 mL of the solution (assuming density of solution = 1 g/ml) **

**Question 4.: Calculate the molarity of a solution of CaCl _{2} if on chemical analysis it is found that 500 mL of CaCl_{2} solution contain 1.505 × 10^{23} Cl^{–} ions**

**Question 5.: 100 ml of a solution containing 5 g of NaOH are mixed with 200 ml of M/5 NaOH solution. Calculate the molarity of the resulting solution. **

**Question 6.: Battery acid is 4.27 M H _{2}SO_{4} and has density of 1.25 g/ml. What is the molality of H_{2}SO_{4} in the solution? **

**Question 7.: The density of a 2.05 M acetic acid in water is 1.02 g/ml. Calculate the molality of the solution **

**Question 8.: ****Calculate the mole fraction of ethylene glycol (C _{2}H_{6}O_{2}) in a solution containing 20 % of C_{2}H_{6}O_{2} by mass.**

**Question 9.: ****A solution of glucose in water is labelled as 10 % (w/w). The density of the solution is 1.20 g/ml. Calculate the (a) molality (b) molarity and (c) mole fraction of each component in solution. **

**Question 10.: Concentrated sulphuric acid has a density 1.9 g/mL and is 99 % H _{2}SO_{4} by mass. Calculate the molarity of sulphuric acid. **

**Question 11.: One litre solution of N/2 HCl is heated in a beaker. It was observed that when the volume of the solution is reduced to 600 mL, 3.25 g of HCl is lost. Calculate the normality of the new solution. **

**Question 12.: If N _{2} gas is bubbled through water at 293 K, how many milli moles of N_{2} gas would dissolve in 1 litre of water. Assume that N_{2} exerts a partial pressure of 0.987 bar. The K_{H} for N_{2} at 293 K is 76.48 k bar.**

**Question 13.: At what partial pressure, oxygen will have solubility of 0.05 g L ^{-1} in water at 293 K? Henry’s constant (K_{H}) for O_{2} in water at 293 K is 34.36 k bar. Assume the density of the solution to be same as that of the solvent. **

**Question 14.: Air contain O _{2} and N_{2} in the ratio of 1 : 4. Calculate the ratio of solubilities in term of mole fraction of O_{2} and N_{2} dissolved in water at atmospheric pressure and room temperature at which Henry’s constant for O_{2} and N_{2} are 3.30 × 10^{7} torr and 6.60 × 10^{7} torr respectively. **

**Question 15.: Henry’s law constant for CO _{2} in water is 1.67 × 10^{8} Pa at 298 K. Calculate the quantity of CO_{2} in 500 mL of soda water when packed under 2.5 atm CO_{2} pressure at 298 K.**

**Question 16.: Vapour pressure of chloroform (CHCl _{3}) and dichloromethane (CH_{2}Cl_{2}) at 298 K are 200 mmHg and 415 mmHg respectively. Calculate the (a) Vapour pressure of the solution prepared by mixing 25.5 g of CHCl_{3} and 40 g of CH_{2}Cl_{2} at 298 K and (b) Mole fraction of each component in vapour phase.**

**Question 17.: The vapour pressure of ethyl acetate and ethyl propionate are 72.8 and 27.7 mmHg respectively. A solution is prepared by mixing 25 g of ethyl acetate and 50 g of ethyl propionate. Assuming the solution to be ideal, Calculate the vapour pressure of the solution. **

**Question 18.: At 298 K, the vapour pressure of pure benzene is 0.256 bar and vapour pressure of pure toluene is 0.925 bar. If the mole fraction of benzene in solution is 0.40, find the total vapour pressure of solution. Also find the mole fraction of toluene in vapour phase. **

**Question 19.: The vapour pressure of pure liquids A and B are 450 and 700 mmHg respectively, at 350 K. Find out the composition of the mixture if total vapour pressure is 600 mmHg. Also find the composition of the vapour phase. **

**Question 20.: The vapour pressure of pure benzene at a certain temperature is 0.850 bar. A non-volatile and non-electrolyte solid weighing 0.5 g is added to 39.0 g of benzene (molar mass 78 g/mol). The vapour pressure of the solution then is 0.845 bar. What is the molar mass of the solid substance? **

**Question 21.: The vapour pressure of 2.1 % of an aqueous solution of non-electrolyte at 373 K is 755 mm. Calculate the molar mass of solute. (Consider that vapour pressure of water at 373 K is 760 mm). **

**Question 22.: 20 g of solute was added to 100 g of water at 25 ˚C. The vapour pressure of water and that of the solution were 23.76 mmHg and 22.41 mmHg respectively at that temperature. Calculate the relative molecular mass of the solute. **

**Question 23.: A solution of glycerol (C _{3}H_{8}O_{3}), in water was prepared by dissolving some glycerol in 500 g of water. This solution has a boiling point of 100.42 ˚C. What mass of glycerol was dissolved to make the solution? K_{b} for water = 0.52 K kg/mol. **

**Question 24.: 18 g of glucose, C _{6}H_{12}O_{6}, is dissolved in 1 kg of water. At what temperature will the water boil at 1.013 bar pressure ? K_{b} for water is 0.52 K kg/mol. **

**Question 25.: The boiling point of benzene is 353.23 K. When 1.80 g of a non-volatile solute was dissolved in 90 g of benzene, the boiling point is raised to 354.11 K. Calculate the molar mass of the solute. K _{b} for benzene is 2.53 K kg/mol. **

**Question 26.: 45 g of ethylene glycol (C _{2}H_{6}O_{2}) is mixed with 600 g water. Calculate : (a) freezing point of depression (b) freezing point of solution. (K_{f} for H_{2}O = 1.86 K kg/mol) **

**Question 27.: What mass of ethylene glycol (Molecular mass = 62.0 g/mol) must be added to 5.50 kg of water to lower the freezing point of water from 0 ˚C to -10.0 ˚C. (K _{f } H_{2}O is 1.86 K kg/mol). **

**Question 28.: 1.00 g of non-electrolyte solute dissolved in 50 g of benzene lowered the freezing point of benzene by 0.40 K. K _{f} of benzene is 5.12 K kg/mol. Find Molar mass of solute.**

**Question 29.: 200 cm ^{3} of an aqueous sol^{n} of protein contains 1.26 g of protein. Osmotic pressure of this solution at 300 K is found to be 2.57 × 10^{-3} bar. Calculate molecular mass of protein. **

**Question 30.: 10 g of a substance were dissolved in water and solution was made up to 250 cm ^{3}. Osmotic pressure of solution was found to be 8 10^{5} Nm^{-2} at 288 K. Find molar mass of solute. **

**Question 31.: The osmotic pressure of blood is 8.21 atm at 37 ˚C. How much glucose would be used for an injection that is at the same osmotic pressure as blood ? (R= 0.0821 atm mol ^{-1} K^{-1}]**

**Question 32.: 2 gm of benzoic acid (C _{6}H_{5}COOH) dissolved in 25 g of benzene shows a depression in freezing point equal to 1.62 K. Molal depression constant for benzene is 4.9 K kg mol^{–1}. What is the percentage association of acid if it forms dimer in solution?**

**Question 33.: 0.6 mL of acetic acid having density of 1.06 gm/ml is dissolved in 1 Litre of water. The depression in freezing point observed for this strength of the acid was 0.0205 °C. Calculate the Van’t Hoff factor and the dissociation constant of the acid. K _{f} for water = 1.86 K Kg mol^{-1}. **

**Question 34.: ****0.5 gm KCl was dissolved in 100 gm water and the solution originally at 20 °C, froze at 0.24 °C. Calculate the percentage ionization of salt. K _{f} for water = 1.86 K Kg mol^{-1}.**

**Question 35.: Calculate the freezing point depression expected for 0.0711 molal aqueous solution of Na _{2}SO_{4}. If this solution actually freezes at 0.32 °C, What would be the value of Van’t Hoff factor ? K_{f} for water = 1.86 K Kg mol^{-1}.**

**Question 36.: What mass of NaCl must be dissolved in 65 gm of water to lower the freezing point by 7.5 °C ? K _{f} for water = 1.86 K Kg mol^{-1}. Assuming that Van’t Hoff factor for NaCl is 1.87. **

**Question 37.: Calculate the boiling point of a solution prepared by adding 15 gm of NaCl to 250 gm of water (K _{b }for water = 0.52 K Kg mol^{-1}).**

#### Boost your self-study.

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