Q1. What name is given to a solution of iodine in alcohol?
Ans. Tincture of iodine.
Q2. What is the homogeneous mixture of two or more metals called?
Q3. When water and coconut oil are mixed, the mixture formed is called?
Ans. Heterogeneous mixture.
Q4. Name the method that can be used to separate the mixture of camphor and potassium chloride.
Ans. Sublimation method.
Q5. What are the two elements which are liquid at room temperature?
Ans. Mercury and bromine.
Q6. Which category of elements is represented by silicon and tin
Ans. Metalloid elements.
Q7. What is the cause of Tyndall effect?
Ans. Scattering of light by the colloidal particles.
Q8. Name the shining element used in thermometers. What is its physical state?
Ans. Mercury, liquid.
Q9. Name a solution in which both solute as well as solvent are liquid.
Ans. Solution of alcohol and water.
Q10. What happens when a colloidal sol of sulphur is rotated in centrifugal machine?
Ans. Yellow residue of sulphur will settle at the bottom of the tube.
Q11. What are alloys?
Ans. Alloys are mixture of two or more metals or a metal and a non -metal and cannot be separated into their components by physical methods. Alloys are considered as mixtures as they show the properties of its constituents and can have variable composition.
Q12. What type of changes are involved when ̎candle burns”?
Ans. Burning of candle involves both chemical as well as physical changes. During burning the solid wax melts into liquid and then changes into vapours. These changes are physical changes. The vapours further go under combustion to form carbon dioxide and water. These changes involve the formation of new compounds. Thus, it is a chemical change.
Q13. The ̔̀sea water΄can be classified as a homogeneous as well as heterogenous mixture comment.
Ans. Sea water contains large number of dissolved salts with some insoluble impurities like slit brought by different rivers. The dissolved salts from homogeneous mixture and insoluble impurities form heterogenous mixture.
Q14. Smoke and fog both are aerosols. In what way are they different?
Ans. Dispersion medium of both smoke and fog is same i.e., air but their dispersed phases are different. In smoke the dispersed phase is carbon particles and in fog dispersed phase is water.
Q15. Give some examples of Tyndall effect from your surroundings.
Ans. Examples of Tyndall effect are:
- Visibility of path light when it passed through fog.
- Visibility of path light when it enters in the dark room through the silt due to scattering of light by dust particles.
Q16. Paediatric medicines are generally labelled as “oral suspension”. Why?
Ans. Paediatric medicines are labelled as “oral suspension” because medicines are generally given to the children through mouth. These medicines are in the form of colloidal particles suspended in water.
Q17. Is air a mixture or compound? Justify.
Ans. Air is a mixture and not a compound.
- Liquid air does not have a fixed boiling point.
- Components of air are nitrogen, oxygen and other gases.
- Components of air can be separated by fractional distillation of liquid air.
Q18. Why are particles in a true solution cannot be seen with naked eyes?
Ans. Particles size in a true solution cannot be seen with naked eyes as its size is less than 1nm and are too small to scatter the beam of light.
Q19. Why does a saturated solution become unsaturated on heating?
Ans. A saturated solution become unsaturated on heating because solubility of most substances increases with rise in temperature.
Q20. Curdling of milk is a chemical change. Justify.
Ans. Curdling of milk represents a chemical change because milk and curd do not have same characteristics and it is a permanent change which cannot be reversed.
Q21. What is the meaning of solubility of a solute? How does it change with variation in temperature?
Ans. The amount of solute required to prepare a saturated solution with a given quantity of solvent at a given temperature is known as solubility of a solute. For example, solubility of sodium chloride (NaCl) in water is 36.0 g at 20˚C. It means that we can dissolve a maximum of 36.0 g of sodium chloride in 100 g of water at 20˚C.
A solution which is saturated can become unsaturated if temperature is increased. If a saturated solution at some higher temperature is cooled, then some of the dissolved solute starts separating in the form of crystals.
Solubility is expressed in terms of mass of solute in grams required to prepare a saturated solution by dissolving in 100 g of solvent.
Q22. You are given a mixture containing sand, iron filings, ammonium chloride and sodium chloride. Describe the procedure you would use to separate these constituents from mixture.
Ans.
(i) Iron fillings can be separated by magnet because except iron, all other are non-magnetic.
(ii) The remaining mixture have ammonium chloride, sodium chloride and sand. From this, ammonium chloride can be separated by the sublimation process.
(iii) The remaining mixture contains common salt and sand. It is dissolved in water, when common salt dissolves while sand remains undissolved and can be separated by filtration. The filtrate can be evaporated to get common salt.
