Class 9 Science Chapter 2 Question Answers - Is Matter Around Us Pure?

Q1: What is chromatography? What is its advantage over other methods of separation?
Ans: Chromatography is the process to separate different components of a mixture by absorbing over a suitable absorber.
The main advantages of this technique is : 

• It can be used for small amount of mixture. 
• Component of mixture do not get wasted. 
• Constituent of mixture can be identified apart from separation.

Q2: Explain sublimation process with labelled diagram.
Ans: The process of converting solid form directly into vapour form is called sublimation. This is a reversible process.
Process : 
(i) Take some camphor or ammonium chloride.
(ii) Crush the compound and put it in china dish.
(iii) Fit an inverted funnel over the china dish.
(iv) Put a cotton ball on the stem of the funnel.
(v) Heat the china dish slowly and observe.
Figure: Separation of ammonium chloride and salt by sublimation

Ammonium chloride is the molecule which on heating changes directly into gaseous state. When vapours of ammonium chloride collected then solid ammonium chloride is formed.

Observation : A change of state directly from solid to gas without changing into liquid state (or vice versa) is observed, this phenomenon is called sublimation.

Q3: What are colloids? Give their characteristics.
Ans: Colloidal solution is a heterogeneous mixture whose particles are bigger than size of particle in solution but cannot be visible by naked eye. When the beam of light passes through a colloid, then the path of light becomes visible. For example : Milk, smoke, etc.
(i) Brownian movement : The particles of a colloid show Brownian movement. The particles in it never fully settle down even leaving for a long time to remain undisturbed. They show constant zigzag movement. The type of movement is caused by the constant collisions between the particles of the dispersing medium and dispersed phase.
(ii) Tyndall effect : If the beam of light passes through a colloid then the path of light becomes visible. This is called Tyndall effect. The colloidal particles shine because they scatter the light falling on them in all directions.
Figure: Colloidal solution

Q4: 110 g solution of salt is present in 550 g of solution. Calculate the concentration of solution.
Ans:  Mass of solute = 110 g
Mass of solution = 550 g
 % composition = 110 x 100 / 550
Concentration = 20% by mass

Q5: How much water should be mixed with 12 ml of alcohol to obtain 12% of alcohol? Calculate.
Ans:
Volume of solute = 12 ml
Concentration of solution = 12%
Volume of water = x
We know that
Concentration of solution = Volume of Solute / Volume of Solution x 100

100 = 12 + x
x = 100 – 12
x = 88 ml
Volume of water = 88 ml

Q6: Calculate the grams of NaCl (5.25% by mass) in 245 grams of a commercial bleach solution.
Ans:
Mass percent =  Gram of solute / Gram of solution x 100
 Solute (gram ) = Mass percent / Gram of solution x 100
= 5.25 x 245 / 100
= 12.9 g

Q7: Give difference between colloidal solutions and suspensions.
Ans:


Q8: What is chromatography? What is its advantage over other methods of separation?
Ans: Chromatography is the process to separate different components of a mixture by absorbing over a suitable absorber. The main advantages of this technique is :
(i) It can be used for small amount of mixture.
(ii) Component of mixture do not get wasted. (iii) C onstituent of mixture can be identified apart from separation.

Q9: Give difference between true solutions and colloidal solutions.
Ans: