Question:
What principle is applied in centrifugation? Give examples where this method is applied to separate mixtures.
Answer:
Centrifugation works on the principle that that the denser particles are forced to the bottom and the lighter particles stay at the top when spun rapidly. Examples are:
- Separating cream from milk (cream comes as top layer)
- Used in diagnostic laboratories for blood and urine tests.
- Used in washing machines to squeeze out water from wet clothes.
- Used in preparing lactic cultures to prepare cheese (paneer) from milk in dairies.
Is Matter Around Us Pure?
Q 1.
Choose one term from the following which includes the other three :
aerosol,
emulsion,
colloid,
sol
Q 2.
(a) What is meant by (i) elements (ii) compounds, and (iii) mixtures ? Write down the names of two elements,two compounds and two mixtures.
(b) Classify the following into elements,
compounds and mixtures :
Marble,
Air,
Gold,
Brass,
Sand,
Diamond,
Graphite,
Petroleum,
Common salt,
Sea-water,
Chalk
Q 3.
Name the property of any one of the components which can be used for separating the following mixture : Salt and Camphor
Q 4.
What are different ways to separate solid mixtures?
Q 5.
Classify the following as physical or chemical changes :
(i) Cooking of food
Q 6.
What is the general name of the process by which tea-leaves are separated from prepared tea ?
Q 7.
Name one pair of substances whose mixture can be separated completely by distillation.
Q 8.
Define a compound. Give two points of evidence to show that sodium chloride is a compound.
Q 9.
Name any two solid substances whose mixture can be separated by sublimation.
Q 10.
What are the properties of a colloid?
Q 11.
Name the source from which nitrogen and oxygen are obtained on a large scale.
Q 12.
Name the elements are in liquid state at room temperature.
Q 13.
In beaker A, sugar cubes are dissolved into water while in beaker B, crushed cubes are taken. In which beaker the rate of dissolution is faster?
Q 14.
What is meant by a pure substance?
Q 15.
What are the physical states of dispersed phase and dispersion medium of a cloud?
Q 16.
What are the physical states of dispersed phase and dispersion medium of a fog?
Q 17.
Name the process you would use to separate ammonium chloride from a mixture of sodium chloride and ammonium chloride.
Q 18.
Name the property of one of the constituents which can be used to separate a mixture of salt and iodine
Q 19.
Name the process by which the various gases of the air are separated.
Q 20.
What are different categories of pure substance?
Q 21.
What are the kinds of mixture?
Q 22.
What are the various methods to express concentration of a solution?
Q 23.
Name a non-metal which is a good conductor of electricity.
Q 24.
Name the process which is used in milk dairies to separate cream from milk.
Q 25.
Why do fish go in deep waters during day light?
Q 26.
What are the advantages of preparing solutions?
Q 27.
How crystallization is better than evaporation?
Q 28.
Name the following :
(a) a lustrous liquid metal.
(b) a liquid non-metal
(c) a metal which can be cut with a knife
(d) a non-metal which is good conductor of electricity.
(e) an element which melts when kept on the palm.
(f) the best conductor of heat.
Q 29.
How many elements are there which are in gaseous state at room temperature?
Q 30.
Which of the following is a mixture ?Salt, Air, Water, Alum, Sugar
Q 31.
Which of the following will show Tyndall effect ? Why ?
(a) Salt solution
(b) Starch solution
(c)Milk
Q 32.
Name one pair of liquids which can be separated by using a separating funnel.
Q 33.
On the basis of composition, how matter is classified?
Q 34.
Alloys cannot be separated by physical means, though it is considered mixture, Why?
Q 35.
Why air is a mixture not a compound? Give reasons.
Q 36.
What are the properties of suspensions?
Q 37.
Explain with an example what is a colloid?
Q 38.
What do you mean by strength of the solution?
Q 39.
A good method to separate alum (phitkari) from impure samples is
(a) Filtration
(b) Sedimentaion
(c) Crystallization
(d) Sublimation
Q 40.
Identify the following as mixture or compound.
(i) blood
(ii) common salt
(iii) sugar
(iv) brass
Q 41.
How much water should be mixed with 12 mL of alcohol so as to obtain 12 % alcohol solution ?
Q 42.
A 5 per cent sugar solution means that:
(a)5 g of sugar is dissolved in 95 g of water.
(b)5 g of sugar is dissolved in 100 g of water.
Choose the correct answer.
Q 43.
What is the difference between solutions and colloids ?
Q 44.
What is difference between colloids and suspensions ?
Q 45.
What type of magnet is fitted on a crane to separate scrap iron objects from a heap of waste materials in factories ?
Q 46.
Name one pair of substances whose mixture can be separated by fractional distillation.
Q 47.
Which technique can be used to detect and identify traces of poison present in the stomach wash of a person ?
Q 48.
List the points of differences between homogeneous and heterogeneous mixtures.
Q 49.
What are non-aqueous solutions?
Q 50.
To make a saturated solution, 36 g of sodium chloride is dissolved in 100 g of water at 293K. Find its concentration at this temperature.
