punjab text book notes 9th chemistry

1. Chapter 6 solutions
ADNAN SOHAIL
M. Phil chemistry
1. Why is a solution considered mixture?
Ans. It is considered a mixture as:
The components of solution can be separated by physical means.
It shows the properties of its components and
It has a variable composition.
2. Distinguish between the following pairs as compound or solution:
(a) water and salt solution (b) vinegar and benzene
(c) carbonated drinks and acetone
Ans.
(a) water is a compound and salt solution is a solution
(b) vinegar is a solution and benzene is a compound
(c) carbonated drinks are solutions and acetone is a compound
3. What is the major difference between a solution and a mixture?
Ans. A solution exists as one phase whereas a mixture exists in more than one phase.
4. Why the alloys are considered solutions?
Ans. Alloys are considered solutions because an alloy like brass or bronze is also a
homogeneous mixture.
5. Dead sea is so rich with salts that it forms crystals when temperature lowers in the
winter. Can you comment why is it named as “Dead Sea”?
Ans. It is called the Dead Sea because its salinity prevents the existence of any life forms in
the sea.
1. Does the percentage calculations require the chemical formula of the solute ?
Ans. the percentage calculations does not require the chemical formula of the solute.
Because molar mass is not required in these calculations.
2. Why is the formula of solute necessary for calculation of the molarity of the solution?
Ans. It is because in molarity calculations, formula of solute is used to calculate molar mass
and moles of solute.
3. You are asked to prepare 15 percent (m/m) solution of common salt. How much
amount of water will be required to prepare this solution ?
Ans. To make 15 percent (m/m) solution of common salt, 15g of salt is mixed with 85g of
water so that total mass of solution becomes 100g.
1

2. Chapter 6 solutions
ADNAN SOHAIL
M. Phil chemistry
4. How much water should be mixed with 18 cm3
of alcohol so as to obtain 18 % (v/v)
alcohol solution?
Ans. To obtain 18 % (v/v) alcohol solution, 82 cm3
water is mixed in 18 cm3
of alcohol so
that total volume of solution becomes 100 cm3
.
5. Calculate the concentration % (m/m) of a solution which contains 2.5 g of salt
dissolved in 50 g of water?
Ans.
Mass of solution = 50 + 2.5 = 52.5g
% mass / mass = mass of solute (g) x100
mass of solution (g)
= 2.5x100
52.5 = 4.76%
6. Which one of the following solutions is more concentrated: one molar or three molar?
Ans. Three molar solution contains more amount of solute so it is more concentrated than
one molar solution.
1. What will happen if the solute-solute forces are stronger than those of solute-solvent
forces?
Ans. if the solute-solute forces are stronger than those of solute-solvent forces then solute
will remain insoluble in solvent.
2. When solute-solute forces are weaker than those of solute-solvent forces? Will
solution form?
Ans. If solute-solute forces are weaker than those of solute-solvent forces then solute
dissolves and is solution formed.
3. Why is iodine soluble in CCI4 and not in water.
Ans. According like dissolves like principle Iodine being nonpolar substance, dissolves in a
nonpolar solvent CCl4. It does not dissolve in water. It is because water is a polar solvent.
4. Why test tube becomes cold when KNO3 is dissolved in water?
Ans. The test tube becomes cold when KNO3 is dissolved in water because dissolution of
KNO3 is an endothermic process.
2

3. Chapter 6 solutions
ADNAN SOHAIL
M. Phil chemistry
1. What is difference between colloid and suspension?
Ans. Colloids are solutions in which solute particles are larger than those present in the
true solutions but not large enough to be seen by naked eye. The particles in such system
dissolve and do not settle down for a long time.
Suspensions are a heterogeneous mixture of undissolved particles in a given medium.
Particles are big enough to be seen with naked eyes. Examples are chalk in water.
2. Can colloids be separated by filtration, if not why?
Ans. Although particles are big but they can pass through a filter paper. Hence they can’t be
separated by filtration process.
3. Why are the colloids quite stable?
Ans. Particles of colloids do not settle down for a long time. Therefore, these are quite
stable.
4. Why does the colloid show tyndall effect?
Ans. The particles of colloids are big enough to scatter the beam of light. That’s why they
show Tyndall effect.
5. What is tyndall effect and on what factors it depends?
Ans. Scattering of beam of light into different directions when passed through a colloid
solution is called Tyndall effect.
It depends upon following factors:
1) wavelength of the light used
2) Size of colloid particles.
6. Identify as colloids or suspensions from the following: Paints, milk, milk of magnesia,
soap solution?
Ans.
Colloids: Milk, soap solutions, Blood, Starch, albumin, ink,
jelly and toothpaste
Suspensions: paints, milk of magnesia, chalk in water
7. How can you justify that milk is a colloid?
Ans.
Its particles do not settle down for a long time.
It shows tyndall effect by scattering the beam of light.
Its particles are large but can’t be seen by naked eye.
Although its particles are large but they can pass through filter paper.
3

4. Chapter 6 solutions
ADNAN SOHAIL
M. Phil chemistry
SHORT ANSWER QUESTIONS
1. Why suspensions and solutions do not show tyndall effect, while colloids do?
Ans. The particles of suspension are so big that instead of scattering they block the beam
of light. The particles of solutions are too small to show tyndall effect. On the other hand, the
particles of colloid scatter the beam of light and show tyndall effect.
2. What is the reason for the difference between solutions, colloids and suspensions?
Ans. The basic difference between these three type of solutions is that of particle size.
3. Why the suspension does not form a homogeneous mixture?
Ans. The particles of suspension due to large size remain undissolved in solvent and form
heterogeneous mixture.
4. How will you test whether given solution is a colloidal solution or not?
Ans. A solution which shows tyndall effect is a colloidal solution.
5. Classify the following into true solution and colloidal solution: Blood, starch solution,
glucose solution, toothpaste, copper sulphate solution, silver nitrate solution.
Ans.
True Solution: glucose solution, copper sulphate solution, silver nitrate solution.
Colloidal solution: Blood, starch solution, toothpaste.
6. Why we stir paints thoroughly before using?
Ans. Paints are examples of suspensions. Particles of suspensions are of big size and settle
down after sometime. To make a true solution we need to stir paints before use.
7. Which of the following will scatter light and why? sugar solution, soap solution and
milk of magnesia.
Ans. sugar solution is a ture solution. Soap solution is a colloid and milk of magnesia is a
suspension. Only soap solution will scatter light because it has colloidal size particles.
8. What do you mean, like dissolves like? Explain with examples
Ans. Like dissolves like means:
The ionic and polar substances are soluble in polar solvents. e.g. common salt,
sugar, and alcohol are all soluble in water.
Non-polar substances are not soluble in polar solvents. e.g. ether, benzene, and
petrol are insoluble in water.
Non-polar covalent substances are soluble in non-polar solvents. e.g. Grease and
paints are soluble in ether and carbon tetrachloride.
9. How does nature of attractive forces of solute-solute and solvent-solvent affect the
solubility?
Ans. If the new forces between solute and solvent particles overcome the solute-solute
attractive forces, then solute dissolves and makes a solution. If forces between solute
particles are strong enough than solute-solvent forces, solute remains insoluble and solution
is not formed.
4

5. Chapter 6 solutions
ADNAN SOHAIL
M. Phil chemistry
10. How you can explain the solute-solvent interaction to prepare a NaCl solution?
Ans. when NaCl is added in water it dissolves readily because the attractive interaction
between the ions of NaCl and polar molecules of water are strong enough to overcome the
attractive forces between Na+
and Cl -
ions in solid NaCl crystal.
In this process, the positive end of the water dipole is oriented towards the CI -
ions and the
negative end of water dipole is oriented towards the Na+
ions. These ion-dipole attractions
between Na+
ions and water molecules, Cl -
ions and water molecules are so strong that they
pull these ions from their positions in the crystal and thus NaCl dissolves.
11. Justify with an example that solubility of a salt increases with the increase in
temperature?
Ans. When salts like KNO3, NaNO3 and KCl are added in water, the test tube becomes cold.
It means during dissolution of these salts heat is absorbed. Such dissolving process is
called ‘endothermic’.
Solubility usually increases with the increase in temperature for such solutes. It means that
heat is required to break the attractive forces between the ions of solute.
12. What do you mean by volume/volume %?
Ans. It is the volume in cm3
of a solute dissolved per 100 cm3
of the solution.
% volume / volume = volume of solute x100
volume of solution
5