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chapter -- ' is matter around us pure ' ...
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Explanation:
Extra Questions for Class 9 Science Chapter 2 Is Matter Around Us Pure
Is Matter Around Us Pure Class 9 Extra Questions Very Short Answer Questions
Question 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.
Question 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. [NCERT Exemplar]
Answer:
It is a pure substance because chemical composition of sugar crystals is same irrespective of its source.
Question 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.
Question 4.
Identify solute and solvent in ‘tincture of iodine’.
Answer:
Iodine is the solute and alcohol is the solvent.
Question 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.
Question 6.
What are the two components of a colloidal solution?
Answer:
The two components of a colloidal solution are dispersed phase and dispersing medium.
Question 7.
In what respect does a true solution differ from a colloidal solution?
Answer:
A true solution is homogeneous whereas a colloidal solution is heterogeneous.
Question 8.
Two liquids ‘A’ and ‘B’ are miscible with each other at room temperature. Which separation technique will you apply to separate the mixture of ‘A’ and ‘B’ if the difference in their boiling points is 27°C?
Answer:
We can separate two miscible liquids by fractional distillation, if both the liquids have difference in their boiling points. So, the mixture of liquids ‘A’ and ‘B’ can be separated by fractional distillation.
Question 9.
Define crystallisation.
Answer:
It is a process that separates a pure solid in the form of its crystals from a solution.
Question 10.
Why is crystallisation technique considered better than simple evaporation to purify solids?
Answer:
Crystallisation is considered better than simple evaporation because
some solids decompose or get charred on heating to dryness.
some impurities may remain dissolved in the solution even after filtration. On evaporation, these contaminate the solid.
Question 11.
Why is water called universal solvent?
Answer:
Water is known as universal solvent because it has the ability to dissolve wide variety of substances.
Question 12.
Which of the following are physical changes?
Melting of iron metal, rusting of iron, bending of iron rod, drawing a wire of iron metal.
Answer:
Melting of iron metal, bending of iron rod and drawing a wire of iron metal are physical changes because there is no change in the chemical composition of iron, only its form is changing.
Question 13.
Name two elements which exist in liquid state at room temperature.
Answer:
Gallium and mercury exist in liquid state at room temperature.
Question 14.
An unknown substance ‘A’ on thermal decomposition produces ‘B’ and ‘C’. What is ‘A’—an element, a compound or a mixture?
Answer:
Unknown substance ‘A’ should be a compound because elements and mixture do not decompose.
Question 15.
Identify the elements from the following substances: sulphur, brine, hydrochloric acid, water, neon, paper, sugar.
Answer:
The elements are sulphur and neon.
Is Matter Around Us Pure Class 9 Extra Questions Short Answer Questions-I
Question 1.
‘Sea water can be classified as homogeneous as well as heterogeneous mixture.’ Comment. [NCERT Exemplar]
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.
Question 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.
Question 3.
Explain why particles of a colloidal solution do not settle down when left undisturbed, while in the case of a suspension they do. [NCERT Exemplar]
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.
Question 4.
Identify colloids and true solutions from the following:
Pond water, fog, aluminium paint, vinegar and glucose solution.
Answer:
True solutions are vinegar and glucose solution. Colloids are fog, aluminium paint.
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Answer:
Question 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.
Question 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.
Question 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.
Question 4.
Identify solute and solvent in ‘tincture of iodine’.
Answer:
Iodine is the solute and alcohol is the solvent.
Question 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.
Question 6.
What are the two components of a colloidal solution?
Answer:
The two components of a colloidal solution are dispersed phase and dispersing medium.
Question 7.
In what respect does a true solution differ from a colloidal solution?
Answer:
A true solution is homogeneous whereas a colloidal solution is heterogeneous.
Question 8.
Two liquids ‘A’ and ‘B’ are miscible with each other at room temperature. Which separation technique will you apply to separate the mixture of ‘A’ and ‘B’ if the difference in their boiling points is 27°C?
Answer:
We can separate two miscible liquids by fractional distillation, if both the liquids have difference in their boiling points. So, the mixture of liquids ‘A’ and ‘B’ can be separated by fractional distillation.
Question 9.
Define crystallisation.
Answer:
It is a process that separates a pure solid in the form of its crystals from a solution.
Question 10.
Why is crystallisation technique considered better than simple evaporation to purify solids?
Answer:
Crystallisation is considered better than simple evaporation because
some solids decompose or get charred on heating to dryness.
some impurities may remain dissolved in the solution even after filtration. On evaporation, these contaminate the solid.
Question 11.
Why is water called universal solvent?
Answer:
Water is known as universal solvent because it has the ability to dissolve wide variety of substances.