Extra Questions for Class 9th: Ch 2 Is Matter Around us Pure (Science) Important Questions Answer Included
Very Short Answer Questions (VSAQs): 1 MarkQ.1 How can you change a saturated solution to an unsaturated solution without adding any more solvent to it?
Answer
By heating the saturated solution, it becomes unsaturated.
Q.2 Sucrose (sugar) crystals obtained from sugarcane and beetroot are mixed together. Will it be a pure substance or a mixture? Give reasons for the same.
Answer
It is a pure substance because chemical composition of sugar crystals is same irrespective of its source.
Q.3 Based on which factor a solution is said to be diluted, concentrated or saturated?
Answer
A solution is said to be diluted, concentrated or saturated on the basis of the amount of solute dissolved in the solution.
Q.4 Identify solute and solvent in 'tincture of iodine'.
Answer
Iodine is the solute and alcohol is the solvent.
Q.5 What is mass per cent of a solution?
Answer
It is defined as the mass in grams of the solute present in one hundred grams of a solution.
Short Answer Questions-I (SAQs-I) : 2 Marks
Q. 1. 'Sea water can be classified as homogeneous as well as heterogeneous mixture.' Comment.
Answer
Sea water is a mixture of salts and water which cannot be separated except by evaporation. Therefore, sea water is considered homogeneous. Sea water also contains mud, decayed plant, etc., other than salts and water, so it is heterogeneous also.
Q.2. Why is it not possible to distinguish particles of a solute from the solvent in solution?
Answer
A true solution is homogeneous in nature. The solute and solvent particles are very small. They cannot be distinguished even under a microscope.
Q. 3. Explain why particles of a colloidal solution do not settle down when left undisturbed, while in the case of a suspension they do.
Answer
Particle size in a suspension is larger than those in a colloidal solution. Also molecular interaction in a suspension is not strong enough to keep the particles suspended and hence they settle down.
Q.4. Identify colloids and true solutions from the following:
Answer
Pond water, fog, aluminium paint, vinegar and glucose solution.
True solutions are vinegar and glucose solution. Colloids are fog, aluminium paint.
Q.5. Give two examples each for: (i) Aerosol, (ii) Emulsion. In what way are they different?
Answer
(i) Aerosol: Clouds, smoke
(ii) Emulsion: Milk, face cream. 0.6. Smoke and fog both are aerosols.
Both fog and smoke have gas as the dispersion medium. The only difference is that the dispersed phase in fog is liquid and in smoke it is a solid.
Short Answer Questions-II (SAQs-II) : 3 Marks
Q. 1. Describe any three properties of colloid.
Answer
(i) It is a heterogenous mixture.
(ii) Size of particles is too small to be seen by naked eye.
(iii) They scatter light passing through them making its path visible.
(iv) They do not settle down when left undisturbed.
(v) They cannot be separated by the process of filtration.
Q. 2. State the principle of separating two immiscible liquids by separating funnel. Describe an activity with diagram to separate a mixture of water and kerosene oil.
Answer
Immiscible layers separate out in layers depending on their densities in separating funnel.
Activity to separate kerosene oil from water using a separating funnel:
• Pour the mixture of kerosene oil and water in separating funnel as shown in figure.
• Let it stand undisturbed for sometime so that separate layers of oil and water are formed.
• Open the stopcock of the separating funnel and pour out the lower layer of water carefully.
• Close the stopcock of the separating funnel as the oil reaches the stopcock.
Q3. What would you observe when:
(a) a saturated solution of potassium chloride prepared at 60°C is allowed to cool at room temperature?
(b) an aqueous sugаr solution is heated to dryness?
(c) a mixture of iron filings and sulphur powder is heated strongly?
Answer
(a) Solid potassium chloride will separate out.
(b) Initially the water will evaporate and then sugar will get charred.
(c) Iron sulphide will be formed.
Long Answer Questions (LAQs) : 5 Marks
Q. 1. Differentiate between a true solution and a colloid.
Answer
True solution
|
Colloid
|
| A true solution is a homogeneous mixture of two or more substances. | A colloidal solution is a heterogeneous mixture of two substances. |
| The size of the particles is less than one nanometer. | The range of particle size is between one nanometer to 1000 nanometer. |
| It is always transparent. | It is translucent. |
| The particles cannot be seen even with microscope. | The particles of a colloidal solution can be seen with microscope. |
| It does not show Tyndall effect. | It shows Tyndall effect. |
Q. 2. Distinguish between physical change and chemical change.
Answer
Physical change
|
Chemical change
|
| In a physical change, only physical properties such as colour, physical state, density, volume etc. change, chemical properties remain unchanged. | In a chemical change, the chemical composition and chemical properties undergo a change. |
| No new substance is formed in a physical change. | A new substance is formed in a chemical change. |
| Very little or no energy in the form of heat, light or sound is usually absorbed or given out in physical change. | A chemical change is always accompanied by a absorption or evolution of energy. |
| A physical change is a temporary change. | A chemical change is a permanent change. |
| The original form of substance can be regained by simple physical methods. | Original substance cannot be obtained by simple physical methods. |
| A physical change is reversible. | A chemical change is irreversible. |