Chp 1 Solutions board exam questions
HSC Exam 10 Years Que Ans
Multiple Choice Questions
- Among the following equimolar aqueous solutions, identify the one having highest boiling point.
[Mar 08]
(A) Urea
(B) Sucrose
(C) Sodium chloride
(D) Sodium sulphate
2. The addition of non-volatile solute into the pure solvent
[Oct 08]
(A) increases the vapour pressure of solvent
(B) decreases the boiling point of solvent
(C) decreases the freezing point of solvent
(D) increases the freezing point of solvent
3. Which of the following solutions shows maximum depression in freezing point?
(A) 
(B)
(C)
(D)
4. The temperature at which vapour pressure of a liquid becomes equal to the atmospheric pressure is
(A) melting point
(C) 
(B) boiling point
(D) 
[Oct 13]
5. Which of the following is 
a colligative property?
[Mar 14]
(A) Vapour pressure
(B) Depression in freezing point
(C) Elevation in boiling point
(D) Osmotic pressure
6. Colligative property depends only on in a solution.
[Mar 15]
(A) number of solute particles
(B) number of solvent particles
(C) nature of solute particles
(D) nature of solvent particles
7. The substance ‘ 
‘, when dissolved in solvent water gave molar mass corresponding to the molecular formula ‘ 
‘. The van’t Hoff factor (i) is
[Oct 15]
(A) 3
(B) 0.33
(C) 1.3
(D) 1
8. The determination of molar mass from elevation in boiling point is called as
[Mar 16]
(A) cryoscopy
(B) colorimetry
(C) ebullioscopy
(D) spectroscopy
9. Which of the following 
aqueous solutions will exert the highest osmotic pressure?
(A) 
(B) 
(C) 
(D) 
[Mar 18]
10. In calculating osmotic pressure, the concentration of solute is expressed in
(A) molarity
(C) mole fraction
(B) molality
(D) percentage mass
[Mar 22]
Answers:
1.
(D) 2 .
(C) 3 .
(C) 4
4.
(B)
9. (A) 10 . (A)
(B) 
(C)
- 5 . (A) 6
Solutions:
- The solution having highest number of particles will have highest boling point.
gives 3 ions on complete dissociation. Hence, among the given equimolar aqueous solutions, solution has highest boiling point. 
shows maximum depression in freezing point since 0.5 mole of 
will give the highest number of particles, i.e., 1 mole of 
and 1.5 mole of 
ions as compared to other solutions. 0.5 mole of 
gives: 1.5 mole of ions, 1 mole of 
gives 2 mole of ions and 0.5 mole of 
gives 1.5 mole of ions.- van’t Hoff factor (i)
gives 3 ions on complete dissociation. Hence, among the given equimolar aqueous solutions, 
solution has highest boiling point.
shows maximum depression in freezing point since 0.5 mole of 
will give the highest number of particles, i.e., 1 mole of 
and 1.5 mole of 
ions as compared to other solutions. 0.5 mole of 
gives: 1.5 mole of ions, 1 mole of 
gives 2 mole of ions and 0.5 mole of 
gives 1.5 mole of ions.
- Colligative properties are proportional to the number of solute particles present in the solution.
Osmotic pressure is a colligative property; hence, 
exerts the highest osmotic pressure.
Calculation: For bcc unit cell, 
.
Using formula (i),
Density 
.
Using formula (ii),
Ans: Radius of niobium atom ( 
) is 
.
- Calculate the number of atoms and unit cells present in
of Niobium if it forms body centred cubic structure. The density of Niobium is 
and edge length of unit cell is 
.
of Niobium if it forms body centred cubic structure. The density of Niobium is 
and edge length of unit cell is 
.[July 22]
Solution:
Given: 
Type of unit cell is bcc.
Density ( 
) of niobium is 
,
Edge length (a) 
,
Mass of niobium 
To find: i. Number of atoms in 
of niobium
ii. Number of unit cells in 
of niobium
Formulae: i. Number of atoms in 
of metal 
ii. Number of unit cells in 
of metal 
Calculation: i. For bcc unit cell, 
.
Using formula (i),
Number of atoms in 
of niobium
ii. Using formula (ii),
Number of unit cells in 
of niobium
Ans: i. Number of atoms in 
of niobium is 
ii. Number of unit cells in 
of niobium is 
.
Theory Orestions:
2.4 Solubility
- What is the effect of temperature on solubility of a gas in a liquid?
[Oct 15]
Ans:
i. When gases are dissolved in water, the gas molecules in liquid phase are condensed.
ii. The condensation is an exothermic process.
Hence, the solubility of gases in water decreases with increase in temperature.
- State Henry’s law. How does solubility of a gas in water varies with the temperature?
[Oct 13; July 17]
Ans:
i. Statement: Henry’s law states that the solubility of a gas in a liquid is directly proportional to the pressure of the gas over the solution.
ii. ‘ Refer Subtopic 2.4: Q. No. 1.
- State Henry’s law.
Ans: Refer Subtopic 2.4: Q. No. 2.(i).
2.6 Colligative properties of nonelectrolyte solutions
- Define colligative properties.
[Oct 08]
Ans: The physical properties of solutions that depend on the number of solute particles in solutions and not on their nature are called colligative properties.
2.7 Vapour pressure lowering
- Derive the relationship between relative lowering of vapour pressure and molar mass of non-volatile solute.
[Mar 13, 17]
Ans:
i. The relative lowering of vapour pressure is equal to the mole fraction 
of solute in the solution. That is,
ii. The mole fraction of a component of solution is equal to its moles divided by the total moles in the solution. Thus, 
where, 
and 
are the moles of solvent and solute respectively, in the solution
iii. In dilute solutions, 
and 
. Thus, the mole fraction 
is then given by,
iv. From equations (1) and (2), .
v. Suppose that we prepare a solution by dissolving 
of a solute in 
of solvent. The moles of solute and solvent in the solution are then,
and 
where, 
and 
are molar masses of solvent and solute, respectively.
vi. Substitution of equation (4) into equation (3) yields 
2.8 Boiling point elevation
- What is ‘boiling point’?
[Mar 14]
Ans: The boiling point of liquid is the temperature at which its vapour pressure equals the applied pressure.
- Define ebullioscopic constant.
Write its unit.
[Oct 15]
Ans: Ebullioscopic constant 
) is the boiling point elevation produced by 1 molal solution.
Units of 
:
- Derive the relation between elevation of boiling point and molar mass of solute.
[Mar 18] OR
Derive the mathematical expression between molar mass of a non-volatile solute and elevation of boiling point.
[Mar 20]
OR
How will you determine molar mass of non volatile solute by elevation of boiling point?
[Mar 23]
Ans:
i. The boiling point elevation is directly proportional to the molality of the solution.
Thus,
ii. Suppose we prepare a solution by dissolving 
of solute in 
of solvent.
Moles of solute in 
of solvent 
where, 
is the molar mass of solute.
Mass of solvent 
iii. The molality is expressed as,
Std. XII Sci: Board Questions with Solutions (Chemistry)
iv. Substituting equation (2)
Hence, 
- Define ebullioscopic constant.
[Oct 09; July 22]
Ans: Refer Subtopic 2.8: Q. No. 2. (Definition)
2.9 Depression in freezing point
- Define boiling point. Write the formula to determine molar mass of a solute using freezing point depression method. [Mar 16]
Ans:
i. Refer Subtopic 2.8: Q. No. 1.
ii. The formula to determine molar mass of a solute using freezing point depression method is
- Define: Freezing point. OR
[July 16]
What is freezing point of a liquid? [July 18]
Ans: The freezing point of a liquid is the temperature at which liquid and solid are in equilibrium and the two phases have the same vapour pressure.
- Define :Cryoscopic constant. [Oct 14; July 18]
Ans: Cryoscopic constant is the depression in freezing point produced by 1 molal solution of a non-volatile solute.
- Write mathematical expression between cryoscopic constant and molar mass of solute.
[July 19]
Ans: Refer Subtopic 2.9: Q. No. 1.(ii).
- Write the SI unit of cryoscopic constant.
[Mar 23]
Ans: The SI unit of cryoscopic constant is 
.
2.10 Osmotic pressure
- Define semipermeable membrane. [Mar 18]
Ans: Semipermeable membrane is a film such as cellophane which has pores large enough to allow the solvent molecules to pass through them.
- Define osmotic pressure.
[Mar 20; July 17, 22]
Ans: The hydrostatic pressure (on the side of solution) that stops osmosis is called an osmotic pressure of the solution.
OR
The excess of pressure on the side of the solution that stops the net flow of solvent into the solution through a semipermeable membrane is called osmotic pressure.
- Define the following terms:
i. Isotonic solution [Oct 13; Mar 09, 19, 22]
ii. Hypertonic solution [Mar 19]
iii. Hypotonic solution [Mar 19]
Ans:
i. Two or more solutions having the same osmotic pressure are said to be isotonic solutions.
e.g. For example, 
urea solution and 
sucrose solution are isotonic because their osmotic pressures are equal.
ii. If two solutions have unequal osmotic pressures, the more concentrated solution with higher osmotic pressure is said to be hypertonic solution.
- e.g. For ‘example, if osmotic pressure of sucrose solution is higher than that of urea solution, the sucrose solution is hypertonic to urea solution.
iii. If two solutions have unequal osmotic pressures, the more dilute solution exhibiting lower osmotic pressure is said to be hypotonic solution.
e.g. For example, if osmotic pressure of sucrose solution is higher than that of urea solution, the urea solution is hypotonic to sucrose solution.
- Define osmosis. [Mar 13, 22, 23; July 16, 19]
Ans: The net spontaneous flow of solvent molecules into the solution or from more dilute solution to more concentrated solution through a semipermeable membrane is called osmosis.
- Derive an expression to calculate molar mass of non volatile solute by osmotic pressure measurement.
[Mar 22]
Ans:
i. For very dilute solutions, the osmotic pressure follows the equation,
ii. If the mass of solute in 
litres of solution is 
and its molar mass is 
, then 
.
Substituting the value of 
in equation (1), we get 
This formula can be used for the calculation of molar mass of a nonionic solute (i.e., nonelectrolyte), by osmotic pressure ‘ measurement.
2.11 Colligative properties of electrolytes
- Define van’t Hoff factor. How is it related to the degree of dissociation?
[Oct 14]
Ans:
i. van’t Hoff factor (i) is defined as the ratio of colligative property of a solution of electrolyte divided by the colligative property of nonelectrolyte solution of the same concentration.
ii. The van’t Hoff factor is related to degree of ionization as follows:
or 
where, 
Degree of ionization/dissociation
van’t Hoff factor
Moles of ions obtained from ionization of 1 mole of electrolyte.
Numerical
2.4 Solubility
- What is the concentration of dissolved oxygen at under pressure of one atmosphere if partial pressure of oxygen at is
? (Henry’s law constant for oxygen 
)
under pressure of one atmosphere if partial pressure of oxygen at 
is 
? (Henry’s law constant for oxygen 
)Solution: Henry’s law constant 
,
[Mar 20]
Partial pressure of the gas 
Ans: Concentration of dissolved oxygen is 
.
water at same temperature and partial pressure of 
?
Solution: Henry’s law constant 
,
Pressure of the gas 
Solubility 
Ans: Sólubility of 
gas in water is 
.
2.7 Vapour pressure lowering
- The vapour pressure of pure benzene is
of non-volatile solute is added to 
of benzene, the vapour pressure of solution is 
of 
. Calculate molar mass of solute 
.
of non-volatile solute is added to 
of benzene, the vapour pressure of solution is 
of 
. Calculate molar mass of solute 
.[Mar 16]
Solution:
Given: 
Vapour pressure of pure benzene 
Molar mass of benzene 
Mass of non-volatile solute 
Mass of benzene 
To find: 
Molar mass of non-volatile solute 
Formula: 
Calculation: Using the formula,
Ans: The molar mass of the non-volatile solute is 
.
- Calculate the mole fraction of solute, if the vapour pressure of pure benezene at certain temperature is
and vapour pressure of solution of a solute in benzene is .
and vapour pressure of solution of a solute in benzene is 
.Solution:
Given: 
Vapour pressure of pure benzene 
Vapour pressure of solution 
To find: , Mole fraction of solute 
Formula: 
Calculation: Using the formula,
Ans: The mole fraction of solute is 
.
2.8 – Boiling point elevation
- A solution containing
of camphor (molar mass 
) in of acetone (boiling point 
) boils at 
. A solution of 
of unknown compound in the same weight of acetone boils at . Calculate the molar mass of the unknown compound.
of camphor (molar mass 
) in 
of acetone (boiling point 
) boils at 
. A solution of 
of unknown compound in the same weight of acetone boils at 
. Calculate the molar mass of the unknown compound.[Oct 14]
Solution:
Given: 
Mass of camphor 
, Molar mass of camphor 
Mass̃ of acetone 
, Mass of unknown compound 
To find: 
Molar mass of unknown compound 
Formula: 
Cálculation: For solution of camphor in acetone,
For solution of unknown compound in acetone,
Using the formula,
Ans:- The molar mass of the unknown compound is 
.
of sulphur is dissolved in of 
. This solution boils at . What is molecular formula of sulphur in solution? The boiling point of 
is .
of sulphur is dissolved in 
of 
. This solution boils at 
. What is molecular formula of sulphur in solution? The boiling point of 
is 
.Solution:
[Given that 
for 
and atomic mass of 
.]
Given: 
Mass of sulphur 
, Mass of solvent 
Boiling point of solution 
, Boiling point of pure solvent 
Molal elevation constant 
Atomic mass of sulphur 
To find: 
Molecular formula of sulphur in solution
Formula: 
Calculation: For solution of sulphur in 
(solvent),
From formula,
Now, atomic mass of 
Number of Sulphur atoms in a molecule 
Molecular formula of sulphur in 
Ans: Molecular formula of sulphur in 
‘solution is 
.
- The boiling point of benzene is . When 1.80 gram of non-volatile solute was dissolved in 90 gram of benzene, the boiling point is raised to . Calculate the molar mass of solute. for benzene
. When 1.80 gram of non-volatile solute was dissolved in 90 gram of benzene, the boiling point is raised to 
. Calculate the molar mass of solute. 
for benzene 
[Mar 17]
Solution:
Given:
Boiling point of benzene 
Boiling point of solution 
Mass of non-volatile solute 
Mass of benzene 
To find: 
Molar mass of solute 
Formula: 
Calculation: For solution of non-volatile solute and benzene,
Now, using formula and substituting values,
Ans: The molar mass of non-volatile solute is 
.
- The normal boiling point of ethyl acetate is . A solution of of non-volatile solute in of ethyl acetate boils at . Evaluate the molar mass of solute if
for ethyl acetate is 
.
. A solution of 
of non-volatile solute in 
of ethyl acetate boils at 
. Evaluate the molar mass of solute if 
for ethyl acetate is 
.[July 22]
Solution:
Formula: 
Calculation: For solution of non-volatile solute and ethyl acetate,
Now, using formula and substituting values,
Ans: The molar mass of non-volatile solute is 
.
2.9 Depression in freezing point
of urea when dissolved in 
of a solvent, decreases freezing point of the solvent by 
of another non-electrolyte solute when dissolved in 
of the same solvent depresses the freezing point by 
. Calculate the molar mass of the another solute.
of urea when dissolved in 
of a solvent, decreases freezing point of the solvent by 
of another non-electrolyte solute when dissolved in 
of the same solvent depresses the freezing point by 
. Calculate the molar mass of the another solute.[Given: molar mass of urea 
]
Solution:
For solution containing urea:
Mass of urea 
, Molar mass of urea 
Mass of solvent 
Depression in freezing point of solution containing urea 
For solution containing unknown solute:
Mass of unknown solute 
Mass of solvent 
Depression in freezing point of solution containing unknown solute 
To find: 
Molar mass of unknown solute 
Formula: 
Calculation: Using the formula and rearranging, we get,
From equations (1) and (2),
( 
Since the solvent is same in both solutions, the value of 
will be same for both the solutions.)
Ans: The molar mass of the unknown solute is 
.
- The freezing point of pure benzene is . Calculate the freezing point of the solution when of a solute having molecular weight is added to of benzene.
. Calculate the freezing point of the solution when 
of a solute having molecular weight 
is added to 
of benzene.
of benzene 
Solution:
Freezing point of pure solvent 
Mass of solute 
Molar mass of solute 
Mass of solvent 
Molal depression constant 
To find: 
Freezing point of solution 
Formula: 
Calculation: Rearranging the formula,
Ans: Freezing point of the solution is 
.
aqueous solution of cane sugar has freezing point of 
. Calculate freezing point of glucose solution. [Molar mass of cane sugar 
]
aqueous solution of cane sugar has freezing point of 
. Calculate freezing point of 
glucose solution. [Molar mass of cane sugar 
][July 22]
Solution:
Given: 
Percentage by mass of cane sugar solution 
Percentage by mass of glucose solution 
,
Freezing point of cane sugar solution 
Molar mass of cane sugar 
To find: . Freezing point of glucose solution
Formula: 
Calculation: 
solution (by mass) of cane sugar means that mass of cane sugar 
, and mass of solvent 
.
glucose solution means that mass of glucose 
, and mass of solvent 
.
Molar mass of glucose 
for cane sugar solution 
Now, using the formula,
Rearranging the formula, we get
From equations (1) and (2),
Freezing point of glucose solution 
Ans: Freezing point of glucose solution is 
.
Alternate method:
Formula: 
Calculation: 
solution (by mass) of cane sugar means that mass of cane sugar 
, and mass of solvent 
.
for cane sugar solution 
Now, using formula,
Now, 
glucose solution means that mass of glucose 
, and mass of solvent 
.
Molar mass of glucose 
Using formula,
Freezing point of glucose solution 
Ans: Freezing point of glucose solution is 
.
[Note: In the above problem, the solvent is water and therefore the 
value should be 
and based on this value, 
(glucose) will be 
and 
will be 
. However; we find that on using the alternate method, we get the value of 
as 
.]
2.10 Osmotic pressure
- of a substance dissolved in
of water gave an osmotic pressure of 1.331 atmospheres at . Calculate the molecular weight of the substance.
of a substance dissolved in 
of water gave an osmotic pressure of 1.331 atmospheres at 
. Calculate the molecular weight of the substance.(Given: 
).
[Mar 09]
Solution:
Given:
Volume 
Mass of substance 
Osmotic pressure 
Temperature 
To find: 
Molecular weight 
Formula: 
Calculation: From formula,
Ans: The molecular weight of the solute is 
.
- A solution of a substance having mass has the osmotic pressure of at .
has the osmotic pressure of 
at 
.Calculate the molar mass of the substance used. [Volume 
] [Mar 17]
Solution:
Given: 
Volume 
Mass of substance 
Osmotic pressure 
or 
Temperature 
To find: Molar mass 
Formula: 
Calculation: From formula,
Ans: The molar mass of a solute is 
.
- An organic substance
is dissolved in 
of water. Its osmotic pressure at 
was found to be . If 
, calculate the mass of the solute.
is dissolved in 
of water. Its osmotic pressure at 
was found to be 
. If 
, calculate the mass of the solute.[July 17]
Solution:
Given: 
Volume 
Molar mass of the substance 
Osmotic pressure 
Temperature 
To find:
Mass of the solute 
Formula:
Calculation: From formula,
Ans: The mass of the solute is 
.
2.11 Colligative properties of electrolytes
- Calculate the amount of (van’t Hoff factor ) dissolved in
solution so that its osmotic pressure at is 0.75 atmosphere.
(van’t Hoff factor 
) dissolved in 
solution so that its osmotic pressure at 
is 0.75 atmosphere.Solution:
[Given: Molar mass of 
is 
]
Given: . Osmotic pressure of solution 
Volume of solution 
, van’t Hoff factor 
Temperature 
, Molar mass of solute, 
To find: 
Formula: 
Calculation: Using formula, 
Ans: Amount of 
in the solution is 
.