# chemistry 12 solution chapter 2 exercise 1

CHEMISTRY (CHAPTAR 2)

NCERT EXERCISES WITH ANSWERS EX 2.1

Q – 2.1 Calculate the mass percentage of benzene (C6H6) and carbon tetrachloride (CCI4) is 22 g of benzene is dissolved in 122 g of carbon tetrachloride.
Ans. Mass of solution = Mass of benzene + Mass of carbon tetrachloride
= 22 g + 122g = 144g Q – 2.2. Calculate the mole fraction of benzene in solution containing 30% by mass in carbon tetrachloride.
Ans. 30% of benzene in carbon tetrachloride by mass means that
Mass of benzene in the solution 30 g;           Mass of solution 100 g
؞ Mass of carbon tetrachloride = 100 – 30 g = 70 g ;
Molar mass of benzene (C6H6) = 78 g
mol-1  molar mass of CCI4 = 12 + 4 × 35.5 = 154 g mol-1 Q – 2.3. Calculate the molarity of each of the following solution :
(a) 30 g of Co (NO3)2. 6H2O in 4.3 L of solution (b) 30 ml of 0.5 M H2SO4 diluted to
500 ml.
( Atomic mass of cobalt = 58.7)
Ans. (a) Molar mass of Co(NO3)2.6h2O = 58.7+2(14+48) + 6×18 g mol-1
= 58.7 + 124 + 108 g mol-1 = 290.7 g mol-1 Q – 2.4 Calculate the mass of urea (NH2CONH2) require in making 2.5 kg of 0.25 molal aqueous solution.
Ans. 0.25 molal aqueous  solution of urea means that Q – 2.5. Calculate (a) molality (b) molarity and (c) mole fraction of KI if the density of
20%   (mass/mass) aqueous KI is 1.202 g ml-1.
Ans. 20% (mass/mass ) aqueous KI solution means that
Mass of KI = 20 g,             Mass of solution in water = 100 g
؞  Mass of solvent (water) = 100 – 20 = 80 g = 0.080 kg(a) Calculation of molality
Molar mass of KI = 39 + 127 = 166 g mol-1 Q – 2.6. H2S, a toxic gas with rotten egg like smell, is used for qualitative analysis. If the solubility of H2S in water at STP is 0.195 m, calculate Henry’s law constant.
Ans. Solubility of H2S gas = 0.195 m =0.195 mole in 1 kg of the solvent (water) Q – 2.7. Henry’s law constant for CO2 in water is 1-67 × 108 Pa at 298 K. Calculate the quantity of CO2 in 500 mL of soda water when packed under 2.5 atm CO2 pressure at 298 K. Q – 2.8. The vapour pressures of pure liquid A and B are 450 and 700 mm Hg at 350 K respectively. Find out the composition of the liquid mixture if total vapour pressure is 600 mm Hg. Also find the composition of the vapour phase. Q – 2.9. Vapour pressure of pure water at 298 K is 23.8 mm Hg. 50 g of urea (NH2CONH2) is dissolved in 850 g of water. Calculate the vapour pressure of water for this solution and its relative lowering. Q – 2.10. Boiling point of water at 750 mm Hg is 99.630C. How much sucrose is to be added to 500 g of water such that it boils at 1000C?  Molal elevation constant for water is 0-52 K kg mol-1. Q – 2.11. Calculate the mass of ascorbic acid ( Vitamin C, C6H8O6) to be dissolved in 75 g of acetic acid to lower its melting point by 1.50C.  = 3.9 K g mol-1. Q – 2.12. Calculate the osmotic pressure in pascals exerted by a solution prepared by dissolving 1.0 g of polymer of molar mass 185,000 in 450 ml of water at 370C. Updated: September 19, 2021 — 12:21 pm