Colligative properties
- Which of the following aqueous solution will exhibit highest boiling point? Answer: 3. 0.01M Na₂SO₄ Key idea: elevation of boiling point depends on i× c . Urea: 1×0.01=0.01 . KNO₃ : 2×0.01=0.02 . Na₂SO₄ : 3×0.01=0.03... 1
- The plot of osmotic pressure () vs concentration (mol L^-1) for a solution gives a straight line with slope 25.73 L bar mol^-1. The temperature at which the osmotic pressure measurement is done is:(Use R = 0.083 L bar mol^-1 K^-1) Answer: 2. 37 ^° C Key idea: Π=CRT , so the slope of Π vs C is RT . T=25.73/0.083=310\ K=37^°C Option 2. (310 is in kelvin, not ^° C, so opt... 1
- The following solutions were prepared by dissolving 10 g of glucose (C_6H_12O_6) in 250 ml of water (P_1), 10 g of urea (CH_4N_2O) in 250 ml of water (P_2) and 10 g of sucrose (C_12H_22O_11) in 250 ml of water (P_3). The right option for the decreasi… Answer: 1. P₂ > P₁ > P₃ Key idea: for equal mass in equal volume, osmotic pressure π=CRT is proportional to moles, i.e. inversely proportion... 1
- The right option for the statement "Tyndall effect is exhibited by", is : Answer: 3. Starch solution Key idea: the Tyndall effect needs colloidal particles large enough (1 to 1000 nm) to scatter light. Starch forms... 1
- The freezing point depression constant (K_f) of benzene is 5.12 K kg mol^-1. The freezing point depression for the solution of molality 0.078 m containing a non-electrolyte solute in benzene is (rounded off upto two decimal places) : Answer: 3. 0.40 K Depression in freezing point: Δ T_f=K_f m . Δ T_f=5.12×0.078=0.399≈0.40\ K Option (3) is correct. 1
- If molality of the dilute solution is doubled, the value of molal depression constant (K_f) will be : Answer: 3. unchanged Key idea: K_f is a property of the solvent only. Δ T_f = K_f m . K_f is the depression for a 1 molal solution and depen... 1
- At 100°C the vapour pressure of a solution of 6.5 g of a solute in 100 g water is 732 mm. If K_b = 0.52, the boiling point of this solution will be : Answer: 1. 101°C Key idea: use the lowering of vapour pressure to get the mole fraction, and then the boiling point elevation. At 100°C pure... 1