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.
Which of the following is a mixture ?Salt, Air, Water, Alum, Sugar
Q 4.
Name the process you would use to separate ammonium chloride from a mixture of sodium chloride and ammonium chloride.
Q 5.
Name one pair of liquids which can be separated by using a separating funnel.
Q 6.
Calculate the mass of glucouse and mass of water required to make 200g of 25% solution of glucouse.
Q 7.
Name the property of any one of the components which can be used for separating the following mixture : Salt and Camphor
Q 8.
What is saturated solution? Explain with an example.
Q 9.
How much water should be added to 15 grams of salt to obtain 15 per cent salt solution ?
Q 10.
What are non-aqueous solutions?
Q 11.
Define Brownian movement in colloids.
Q 12.
Name the property :
(a) which allows metals to be hammered into thin sheets.
(b)
Q 13.
What is the concentration of a solution which contains 16 g of urea in 120 g of solution ?
Q 14.
What is meant by solute and solvent?
Q 15.
What is meant by saying that metals are malleable and ductile ?
Q 16.
What are pure substances ? Give two examples of pure substances.
Q 17.
Give two reasons for supposing that water is a compound and not a mixture.
Q 18.
What are the physical states of dispersed phase and dispersion medium of a fog?
Q 19.
Name the technique to separate
(i) butter from curd
(ii) salt from sea-water
(iii) camphor from salt
Q 20.
What is an emulsion? Give examples
Q 21.
Name a non-metal which is a good conductor of electricity.
Q 22.
Name the property of one of the constituents which can be used to separate a mixture of salt and iodine
Q 23.
Name the process which can be used to separate a mixture of salt solution and sand.
Q 24.
Name the apparatus you would use to separate oil from water.
Q 25.
What is a solution? What are the properties of a solution?
Q 26.
What is an unsaturated solution?
Q 27.
Name one pair of substances whose mixture can be separated by fractional distillation.
Q 28.
Name the source from which nitrogen and oxygen are obtained on a large scale.
Q 29.
State the differences between compounds and mixtures.
Q 30.
What principle is applied in centrifugation? Give examples where this method is applied to separate mixtures.
Q 31.
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.
Q 32.
What are different ways to separate solid mixtures?
Q 33.
What are the reasons for separating the constituents of a mixture?
Q 34.
(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 35.
Which of the following will show Tyndall effect ? Why ?
(a) Salt solution
(b) Starch solution
(c)Milk
Q 36.
What are the kinds of mixture?
Q 37.
What are the characteristics of mixture?
Q 38.
List the points of differences between homogeneous and heterogeneous mixtures.
Q 39.
What is supersaturated solution?
Q 40.
What is Chromatography?
Q 41.
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 42.
How many elements are there which are in gaseous state at room temperature?
Q 43.
Identify the following as mixture or compound.
(i) blood
(ii) common salt
(iii) sugar
(iv) brass
Q 44.
Give examples of liquids that are
(i) completely miscible
(ii) partially miscible
(iii) practically immiscible
Q 45.
State whether the following statement is true or false : Milk is a pure substance.
Q 46.
Name a metal which is soft and a non-metal which is hard.
Q 47.
A 15% alcohol solution means :
(a)15 mL alcohol and 85 mL water.
(b)15 mL alcohol and 100 mL water.
Choose the correct answer.
Q 48.
Choose one term from the following which includes the other three :
aerosol,
emulsion,
colloid,
sol
Q 49.
(a) What is meant by a solution ? Give two examples of solutions.
(b)What is a suspension ? Give two examples of suspensions.
(c)
Q 50.
What type of magnet is fitted on a crane to separate scrap iron objects from a heap of waste materials in factories ?
