Question:
How crystallization is better than evaporation?
Answer:
The process of evaporation gives residue which may contain impurities. When there is requirement to obtain solid without impurity, crystallization method is preferred. In general practice, impure solids are obtained by evaporation and are further purified by crystallization. e.g. salt obtained from sea is further purified by this method. In some cases e.g. sugar crystal cannot be obtained by simple evaporation technique because sugar gets charred on heating to dryness. In such cases, crystallization technique is applied.
Is Matter Around Us Pure?
Q 1.
What is the general name of the process by which tea-leaves are separated from prepared tea ?
Q 2.
Classify the following as physical or chemical changes :
(i) Cooking of food
Q 3.
Name the process you would use to separate ammonium chloride from a mixture of sodium chloride and ammonium chloride.
Q 4.
What is meant by solute and solvent?
Q 5.
What are the physical states of dispersed phase and dispersion medium of a fog?
Q 6.
What is saturated solution? Explain with an example.
Q 7.
Name one pair of liquids which can be separated by using a separating funnel.
Q 8.
Name the apparatus you would use to separate oil from water.
Q 9.
Name one pair of substances whose mixture can be separated by fractional distillation.
Q 10.
Which of the following is a mixture ?Salt, Air, Water, Alum, Sugar
Q 11.
How much water should be added to 15 grams of salt to obtain 15 per cent salt solution ?
Q 12.
What are different categories of pure substance?
Q 13.
What are non-aqueous solutions?
Q 14.
Calculate the mass of glucouse and mass of water required to make 200g of 25% solution of glucouse.
Q 15.
Define Brownian movement in colloids.
Q 16.
What are the differences and similarities between concentration and solubility?
Q 17.
State whether the following statement is true or false : Milk is a pure substance.
Q 18.
Name a metal which is soft and a non-metal which is hard.
Q 19.
Name the property :
(a) which allows metals to be hammered into thin sheets.
(b)
Q 20.
What is a solution? What are the properties of a solution?
Q 21.
What are the various methods to express concentration of a solution?
Q 22.
What are pure substances ? Give two examples of pure substances.
Q 23.
Give two reasons for supposing that water is a compound and not a mixture.
Q 24.
Name the property of any one of the components which can be used for separating the following mixture : Salt and Camphor
Q 25.
Name the property of one of the constituents which can be used to separate a mixture of salt and iodine
Q 26.
Name the source from which nitrogen and oxygen are obtained on a large scale.
Q 27.
Name two properties of a substance to check its purity?
Q 28.
List the points of differences between homogeneous and heterogeneous mixtures.
Q 29.
What is an unsaturated solution?
Q 30.
Name the technique to separate
(i) butter from curd
(ii) salt from sea-water
(iii) camphor from salt
Q 31.
Name the elements are in liquid state at room temperature.
Q 32.
Who used the term 'element' first time?
Q 33.
What is the concentration of a solution which contains 16 g of urea in 120 g of solution ?
Q 34.
Name the process which can be used to separate a mixture of salt solution and sand.
Q 35.
What are the kinds of mixture?
Q 36.
What are the properties of suspensions?
Q 37.
What is Chromatography?
Q 38.
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 39.
Give examples of liquids that are
(i) completely miscible
(ii) partially miscible
(iii) practically immiscible
Q 40.
What is meant by saying that metals are malleable and ductile ?
Q 41.
How much water should be mixed with 12 mL of alcohol so as to obtain 12 % alcohol solution ?
Q 42.
Choose one term from the following which includes the other three :
aerosol,
emulsion,
colloid,
sol
Q 43.
What is the difference between solutions and colloids ?
Q 44.
Name one pair of substances whose mixture can be separated completely by distillation.
Q 45.
Name the process which is used in milk dairies to separate cream from milk.
Q 46.
Why do fish go in deep waters during day light?
Q 47.
Based on the type of solvent, how solutions are classified?
Q 48.
What are different ways to separate solid mixtures?
Q 49.
How many elements are there which are in gaseous state at room temperature?
Q 50.
Who gave the first explanatory definition of 'element'?
