CBSE Class 9 Science Practical Skills – Solution, Colloids, Suspension

CBSE Class 9 Science Practical Skills – Solution, Colloids, Suspension

EXPERIMENT

AIM
To prepare

1. A true solution of common salt, sugar and alum.
2. A suspension of soil, chalk powder and fine sand in water.
3. A colloidal solution of starch in water and egg albumin in water and distinguish between these on the basis of
   • transparency
   • filtration
   • stability.

MATERIALS REQUIRED
Test tubes, beakers, water, common salt, sugar, alum, soil, chalk powder, fine sand, egg albumin, starch, funnel, glass rod, filter paper.

THEORY

1. A true solution has particle size < 10^-9 m. It is a homogeneous mixture which is clear and transparent. It passes through the filter paper easily and is stable.
2. Colloid has particle size 10^-9 m- 10^-6 m. It is heterogeneous and is translucerft. It passes through filter paper and is stable.
3. The particle size of Suspension is >10^-6 m. It is heterogeneous and opaque. Its particles do not pass through filter paper and settle under gravity when left undisturbed for sometime.

PROCEDURE
Preparation of solutions/mixtures

1. Take 8 beakers and label them as A, B, C, D, E, F, G and H and add 50 ml of water to each of these beakers.
2. Add samples of salt, sugar and alum to beakers A, B and C. Stir to make clear solution.
3. Add soil, chalk powder and fine sand to beaker D, E and F. Stir for sometime.
4. Add a small amount of starch to the water and boil the content in beaker G.
   In beaker H, add egg albumin and stir vigorously.
5. Observe the mixture and record them in the table given below.

OBSERVATION TABLE

RESULTS

1. Beaker A – Common salt forms a true solution in water.
2. Beaker B – Sugar forms a……………. in water.
3. Beaker C – Alum forms a …………….in water.
4. Beaker D – Soil forms a……………. in water.
5. Beaker E – Chalk Powder forms a……………. in water.
6. Beaker F – Fine sand forms a……………. in water.
7. Beaker G – Starch forms a……………. in water.
8. Beaker H – Egg albumin forms a …………….in water.

PRECAUTIONS

1. Distilled water should be used.
2. The components should be mixed in small amounts.
3. Fold the filter paper properly and moisten it before use.
4. Glass rod should be clean.
5. Wash your hands properly with soap after experiment.

INTERACTIVE SESSION

Examiner:
Define the term solute.
Examinee:
Solute is the dissolved component of a solution, e.g. in a solution of common salt in water, common salt is solute.

Examiner:
What does the term solvent mean?
Examinee:
Solvent is the substance in which the solute is dissolved to get a solution.
For example in a solution of sugar in water, water is the solvent.

Examiner:
Are colloids homogeneous or heterogeneous?
Examinee:
Colloids seem to be homogeneous, but they are actually heterogeneous.

Examiner:
Give two examples of colloids.
Examinee:
Blood, jelly.

Examiner:
Classify as solution, suspension and colloid.
Chalk powder in water, sulphur in water, sulphur in CS₂ , sugar in water, CuS0₄ in water, milk, cloud.
Examinee:
Solution: sulphur in CS₂, CuS0₄ in water, sugar in water.
Suspension: chalk powder in water.
Colloid: sulphur in water, milk, cloud.

Examiner:
What is Tyndall Effect?
Examinee:
The scattering of light by colloidal particles making the path of light visible is called Tyndall effect.

Examiner :
Give an example of a solution in which gas is solute and liquid is solvent.
Examinee:
Aerated drinks.

Examiner:
What is dispersed phase?
Examinee:
The solute like component or dispersed particles in the colloid form dispersed phase.

Examiner:
What is dispersion medium?
Examinee:
The medium in which dispersed phase is suspended is called the dispersion medium.

Examiner:
What are the dispersed phase and dispersion medium in milk?
Examinee:
Fat is the dispersed phase and water is the dispersion mediurfi in milk.

Examiner:
How can fat and water in milk be separated?
Examinee:
By centrifugation.

Examiner:
Why is sky blue in colour?
Examinee:
Because of scattering of light.

Examiner:
What is a gel?
Examinee:
A gel is a colloid in which dispersed phase is a liquid and dispersion medium is a solid.

Examiner:
Is the formation of a true solution from its components a physical or a chemical change?
Examinee:
It is a physical change.

Examiner:
What is a sol? .
Examinee:
A sol is a colloid in which dispersed phase is a solid and the dispersion medium is a liquid. For example paints, milk of magnesia, etc.

Examiner:
What are aerosols?
Examinee:
A colloid in which dispersed phase is either solid or liquid and dispersion medium is gas is called aerosol.

Examiner:
What is Brownian motion?
Examinee:
The zig-zag motion of colloidal particles is called Brownian motion.

Examiner:
Can colloidal particles be seen?
Colloidal particles cannot be seen by naked eye, but can be seen under an electron microscope.

NCERT LAB MANUAL QUESTIONS 

Question 1:
Why are the particles of a true solution not visible to naked eye?
Answer:
The particles of a true solution are not visible to the naked eye as they are very small in size
(less than 1 nm).

Question 2:
What is the order of the size of a particle that can be seen by naked eyes?
Answer:
The size of particles that can be seen by naked eye are of the order of 10-3 mm.

Question 3:
What different techniques of separation can be employed for the separation of components of homogeneous and heterogeneous mixtures?
Answer:
Techniques that can be used to separate the components of a homogeneous mixture are evaporation, distillation, etc., whereas techniques for the separation of the components of heterogeneous mixture are decantation, filtration, boiling, centrifugation, etc.

Question 4:
What will be your observation when a beam of light is passed through a true solution and a suspension respectively?
Answer:
A beam of light when passed through a true solution passes straight through it, whereas light is scattered when passed through a suspension.

Question 5:
What will be the effect of passing light through colloidal solution of sulphur?
Answer:
Light undergoes scattering when it is passed through a colloidal solution of sulphur.

Question 6:
What is the difference in the particle size of colloid, true solution and suspension?
Answer:
Particle size of

1.  Colloid is 1 nm-1000 nm
2. True solution is < 1 nm
3. Suspension is > 1000 nm.

Question 7:
Classify the following as a true solution, suspension or colloid:

1. Milk;
2.  CuS0₄ solution;
3. Jam;
4. Gum;
5. Soil in water
6. Sand in water.

Answer:
True Solution – (2) CuS0₄ solution.
Suspension – (4) Sand in water.
Colloid – (1) Milk, (3) Jam, (4) Gum and (5) Soil in water.

PRACTICAL BASED QUESTIONS
Multiple Choice Questions/VSA

Question 1:
Choose the correct observation about a solution of sugar in water prepared by you in the laboratory.
(a) Its particles are seen by naked eyes.
(b) Its components can be separated by filtra-tion.
(c) Solid particles settle at the bottom after sometime.
(d) It is transparent.

Question 2:
You have prepared four different mixtures in water using
(i) charcoal powder
(ii) chalk powder
(iii) slaked lime
(iv) detergent powder.
If you filter these mixtures through a filter paper, there will be no residue left after filtration in the case of
(a) charcoal powder
(b) chalk powder
(c) slaked lime
(d) detergent powder.

Question 3:
A true solution is
(a) homogeneous
(b) heterogeneous
(c) translucent
(d) opaque.

Question 4:
A solution is transparent blue. It is
(a) a suspension
(b) colloid
(c) true solution
(d) both a colloid and a true solution.

Question 5:
An example of colloid in which dispersed phase is gas and dispersion medium is solid
(a) pumice stone
(b) whipped cream
(c) gemstones
(d) jellies.

Question 6:
Which of the following is stable when allowed to stand undisturbed for sometime?
(a) Sugar solution
(b) Solution of starch in water
(c) Milk
(d) All of the above.

Question 7:
Out of the following, the only incorrect statement is
(a) no residue is left on the filter paper when a colloidal solution is filtered off.
(b) in a colloidal system dispersion medium is a gas.
(c) in a colloidal system dispersion medium is always in the liquid state.
(d) colloidal system is a heterogeneous mixture.

Question 8:
Identify the suspension in the following
(a) soap in water
(6) milk in water
(c) alcohol in water
(d) saw dust in water.

Question 9:
The statement not true for suspensions is
(a) they are transparent
(b) they are unstable
(c) they are heterogeneous
(d) they are opaque.

Question 10:
What is the correct description of a, b and c in the following figure related to the preparation of a true solution?

(a) a = glass rod, b = beaker, c = solution
(b) a = beaker, b = glass rod, c = solution
(c) a = glass rod, b = solution, c = beaker
(d) a = beaker, b = solution, c = glass rod.

Question 11:
A student takes three test tubes A, B and C containing salt solution, starch in water and suspension of sand in water. He pastes small
strips of coloured paper on one side of each test tube. He then observes the coloured paper from the other side of the test tube through the liquid one by one. The correct observation out of the following is
(a) coloured spot is visible in A, not visible in B, appear dim in C.
(b) coloured spot is not visible in A, not visible in B and not visible in C.
(c) coloured spot is not visible in A, appear dim in B, visible in C.
(d) coloured spot is clearly seen in A, appears dim in B, not visible in C.

Question 12:
The correct designation representing the particle size is

Question 13:
Which of the following is true for a mixture of (NH₄)₂C0₃ in water?

Question 14:
Which of the following is true for a mixture of clay in water?

Question 15:
A student carefully observed the colloid of starch in water, human blood and cow milk. On the basis of observations he made, certain conclusions given below. Choose the wrong conclusion.
(a) Components cannot be separated by ordinary filtration
(b) Translucent
(c) Show Tyndall effect
(d) Homogeneous and stable.

ANSWER KEY
Multiple Choice Questions/VSA

1. (d)
2. (d)
3. (a)
4. (c)
5. (a)
6. (d)
7. (c)
8. (d)
9. (a)
10. (a)
11. (d)
12. (c)
13.  (a)
14. (b)
15. (d)
16. (6)
17. (b)

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