UNIT 9: Solutions - Online Test
Q1. For
a solution, the plot of osmotic pressure (p) verses the concentration (c in mol
L–1) gives a straight line with slope 310R where 'R' is the gas
constant. The temperature at which osmotic pressure measured is
Answer : Option C
Explaination / Solution:
π = CRT
y = x (m)
m = RT
310 R = RT
∴ T = 310 K
= 37º C
Q2. 200ml
of an aqueous solution of a protein contains 1.26g of protein. At 300K, the
osmotic pressure of this solution is found to be 2.52 × 10–3 bar.
The molar mass of protein will be (R = 0.083 L bar mol–1K–1)
Answer : Option A
Explaination / Solution:
π = CRT
π = [ W/MV ] . RT
M = WRT / π V
= [1.26 x 0.083x300] / [2.52x10-3x0.2]
= 62.22 Kg mol-1
Q3. The Van't Hoff factor (i) for a dilute aqueous solution of the strong elecrolyte barium hydroxide is
Answer : Option D
Explaination / Solution:
Ba (OH)2 dissociates to form
Ba2+ and 2OH ion
α=(i-1) / (n-1)
i= α(n-1)+1
n=i=3 (for Ba(OH)2),
α =1)
Q4. What is the molality of a 10% W/W aqueous sodium hydroxide solution ?
Answer : Option B
Explaination / Solution:
10% W/W aqueous NaOH solution means that 10 g of sodium
hydroxide in 100g solution
Molality = no. of moles of solute / weight of solvent (in
kg)
= (10/40) / 0.1 =
0.25/0.1 = 2.5M
Q5. The correct equation for the degree of an associating solute, 'n' molecules of which undergoes association in solution, is
Answer : Option C
Explaination / Solution:
α=(1-i)n/(n-1) or n(i-1)/(1-n)
Q6. Which of the following aqueous solutions has the highest boiling point ?
Answer : Option B
Explaination / Solution:
Elevation
of boiling point is more in the case of Na3PO4 (no. of
ions 4 ; 3 Na+, PO43–)
Q7. The
freezing point depression constant for water is 1.86o K Kgmol-1.
If 5g Na2SO4 is dissolved in 45g water, the depression in
freezing point is 3.64oC. The Vant Hoff factor for Na2SO4
is
Answer : Option A
Explaination / Solution:
Q8. Equimolal
aqueous solutions of NaCl and KCl are prepared. If the freezing point of NaCl
is –2ºC, the freezing point of KCl solution is expected to be
Answer : Option A
Explaination / Solution:
Equimolal aqueous solution of KCl also shows 2ºC depression in freezing point.
Q9. Phenol dimerises in benzene having van't Hoff factor 0.54. What is the degree of association ?
Answer : Option D
Explaination / Solution:
i = 0.54
α=(1-i)n/(n-1)
=(1-0.54)2 / (2-1)
α= 0.92
Q10. Assertion
: An ideal solution obeys Raoults Law
Reason : In an ideal solution, solvent-solvent as well as
solute-solute interactions are similar to solute-solvent interactions.
Answer : Option A
Explaination / Solution:
both assertion and reason are correct and reason is the correct explanation of assertion.
