Selina Concise Class 6 Chemistry Solution Chapter No. 5- ‘Pure Substances and Mixtures Separation of Mixtures’ For ICSE Board Students.
(1.) SELECT THE HOMOGENEOUS AND HETEROGENEOUS MIXTURE FROM THE FOLLOWING.
ANS:- HOMOGENEOUS MIXTURE:- Alchohol and water, air dissolved in water, sea water, brass, salt solution.
HETEROGENEOUS MIXTURE:- Sand and charcoal. Air, fruit juice, petrol and water.
(2) DEFINE THE FOLLOWING:-
a) PURE SUBSTANCES:- Pure substance is either element or compound. It contains the same kind of atom or molecules and has a definite set of physical and chemical properties.
b) IMPURE SUBSTANCE:- A substance in which some other substances are also present in smaller or larger amounts is called an impure substance.
c) ALLOY:- A homogeneous solid mixture of two or more metals or a metal and a non metal is called an Alloy.
d) SOLUTION:- The homogeneous mixture of water and a substance soluble in it is called a solution.
e) HETEROGENEOUS MIXTURE:- A mixture in which the components are not uniformally distributed through its volume and can be easily seen separately is called heterogeneous mixture.
f) HOMOGENEOUS MIXTURE:- A mixture in which its constituents are uniformally distributed throughout its volume and cannot be seen separately is called a homogeneous mixture.
(3.) LIST FOUR CHARACTERISTICS OF A MIXTURE.
ANS:- Four characteristics of a mixture are-
1.) mixture retain the properties of its properties.
2.) Mixture has no fixed melting point and boiling points.
3.) Mixture has no fixed composition.
4.) Components of mixture can be separated by simple physical methods.
a) WHY DO SUGAR AND WATER RETAIN THEIR INDIVIDUAL PROPERTIES IN A SUGAR SOLUTION?
ANS:- As a sugar solution is a mixture and mixtures has not any specific set of properties. They show the properties of the individual components from which they are formed.
b) WHY DO PETROL AND WATER FORM A HETEROGENEOUS MIXTURE?
ANS:- Petrol and water forms a heterogeneous mixture as its constituents can be seen separately and are not iuniformly distributed throughout its volume.
c) WHY DOES SULPHUR DISSOLVE WHEN CARBON DISULPHIDE IS ADDED TO A MIXURE OF IRON AND SULPHUR BUT NOT WHEN IT IS ADDED TO IRON SULPHIDE?
ANS:- SULPHUR has the property to dissolve in carbon disulphide whereas iron does not dissolve and retains its individual property. However on heating iron and sulphur they chemically combined forming iron sulphide . In its iron and sulphur particles do not exist separately as such they loose their individual property.
5) GIVE TWO EXAMPLES FOR EACH OF THE FOLLOWING:-
A)SOLID- SOLID:- Sand and iron feeling, Sand and sugar.
B) SOLID-LIQUID:- Salt and water, charcoal and water.
C) LIQUID- GAS:- Cocacola, mist.
d) GAS-GAS:- Air, helium and hydrogen.
6) NAME THE COMPONENTS PRESENT IN THE FOLLOWING MIXTURS:-
A) BRASS- Copper and zinc.
b) Duralumin:- Aluminium, copper and magnesium
c) Tap water:- Air, dissolve salts.
d) Bronze:- copper, Tin, and zinc
7) STATE –A) THREE DIFFERENCES BETWEEN WATER AND AIR.
B) FOUR DIFFERENCES BETWEEN COMPOUNDS AND MIXTURES.
ANS:-A) Three differences are-
1.) A molecule of water is represented by a definite formula H2O.
But air cannot be represents by any chemical formula.
2.) Energy change occurs in the formation of water.
No energy change occurs when components of air are mixed together.
3.) The components of water are hydrogen and oxygen which are chemically combined in a fixed ratio .
And the main components of air are nitrogen, oxygen, carbondi oxide, water vaour.
B) Ans:- Four differences are-
1.) A compound is a pure substance and a Mixture is an impure substance.
2.) Compounds are always homogeneous and mixture may be homogeneous or heterogeneous.
3.) Compounds have specific set of properties and mixture do not have specific set of properties.
a) FILTRATION- The process of separating solid particles from liquid by allowing it to pass through a filter paper is called filtration.
b) SUBLIMATION- The process in which a solid changes directly into its vapours on heating is called sublimation.
c) EVAPOATION- Evaporation is the process of converting a liquid into its vapours state either by exposing it to air or by heating.
d) CRYSTALLISATION- Evaporation of liquid from a homogeneous liquid to solid mixture and collecting solid in the form of crystals is called crystallization.
(2.) WHY DO WE NEED PURE SUBSTANCE?
ANS:- we need pure substance because 1.A pure substance has a fixed melting point and boiling point. 2. Pure substances cannot be broken further into more simple substances by any physical means.
(3.) GIVE ONE EXAMPLES FOR EACH OF THE FOLLOWING TYPES OF MIXTURES.
a) SOLID SOLID HETEROGENEOUS MIXTURE:- Iron and Sulphur.
b) SOLID LIQUID HETEROGENEOUS MIXTURE:- Sand and water.
c) SOLID LIQUID HOMOGENEOUS MIXTURE:- Sugar solution (with Water).
(4.) NAME THE PROCESS BY WHICH THE COMPONENTS OF FOLLOWING MIXTURES CAN BE SEPARATED:-
a) POWDERED GLASS AND SUGAR:- By Filtration process.
b) Chalk powder and Iron feeling:- By Magnetic separation.
c) CHAFF AND GRAIN:- By Winnowing process.
d) SALT AND WATER:- BY evaporation process.
e) WHEAT AND SUGAR:- By Evaporation process.
f) SAND AND CAMPHOR:- By sublimation process.
g) SUGAR AND WATER:- By Crystallisation process.
a) TWO SUBSTANCES WHICH CAN SUBLIME:- Camphor and Napthalene.
b) TWO SUBSTANCES SOLUBLE IN WATER:- Sugar and salt.
c) TWO SUBSTANCES INSOLUBLE IN WATER:- Sand and Chalk powder.
d) FOUR SUBSTANCES THAT CAN BE USED AS FILTERS:- Four substances are- i) a piece of Muslin cloth. Ii) Filter paper. Iii) A bead of sand. Iv) Charcoal.
(6.) GIVE REASONS:-
a) SAND AND SAW DUST CANNOT BE SEPARATED BY HAND PICKING.
ANS:- Sand and saw dust cannot be separated by hand picking because in hand picking method substances should be large enough in size to be recognized and picked out by hand but sand and saw dust particles are very small in size so they can’t be picked by hand. It can be separated by filtration.
b) MAGNET IS USED TO SEPARATE A MIXTURE OF IRON AND SULPHUR.
ANS:- Mixtures of iron and sulphur casn be separated by moving a magnet over them. Iron gets attached to the magnet is separated.
c) ALUM IS USED VIN PURIFICATION OF RIVER WATER.
ANS:- Water from a river, lake contains fine clay particles. To make them settle at a faster rate, a chemical substance called alum in powdered form is added to such mixtures. It dissolves in water and forms clusters with clay and dust particles making them heavier and increasing the rate of sedimentation.