is matter around us pure lesson can i get some mcqs about this lesson
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Explanation:
1. Which of the following statements are true for pure substances?
(i) Pure substances contain only one kind of particles
(ii) Pure substances may be compounds or mixtures
(iii) Pure substances have the same composition throughout
(iv) Pure substances can be exemplified by all elements other than nickel
(a) (i) and (ii)
(b) (i) and (iii)
(c) (iii) and (iv)
(d) (ii) and (iii)
Soln
Answer is b) (i) and (iii)
2. Rusting of an article made up of iron is called
(a) corrosion and it is a physical as well as chemical change
(b) dissolution and it is a physical change
(c) corrosion and it is a chemical change
d) dissolution and it is a chemical change
Soln:
Answer is c corrosion and it is a chemical change.
Explanation :
Rusting of iron is corrosion and it’s a chemical change because rust is a chemical compound called hydrated iron oxide Fe2O3. nH2O, iron(III) which is different from elemental iron.
Physical changes are those changes in which substance identity is not changed and it can get back to its original form ex: water freezing to ice can be melted back to water. Whereas chemical changes are those in which original substance identity is changed and they cannot be restored to their original form.
On adding solid solutes to the solvent, some solute dissolves and its concentration increases in solution. This process is known as dissolution.
Crystallization is a process in which Solute particles in solution collide with the solid solute particles to get separated out of solution.
3. A mixture of sulphur and carbon disulphide is
(a) heterogeneous and shows Tyndall effect
(b) homogeneous and shows Tyndall effect
(c) heterogeneous and does not show Tyndall effect
(d) homogeneous and does not show Tyndall effect
Soln:
A mixture of sulphur and carbon disulphide is a heterogeneous colloid and shows Tyndall effect. In a colloidal solution, the particles are big enough to scatter light. The scattering of light by colloidal particles is known as Tyndall effect. Colloids are actually heterogeneous in nature though they appear to be homogeneous.
Answer is a) heterogeneous and shows Tyndall effect.
Explanation:
A mixture of sulphur and carbon disulphide is heterogeneous and shows Tyndall effect because in a colloidal solution the particles are big enough to scatter light.
4. Tincture of iodine has antiseptic properties. This solution is made by dissolving
(a) iodine in potassium iodide
(b) iodine in vaseline
(c) iodine in water
(d) iodine in alcohol
Soln:
Answer is (d) iodine in alcohol
Explanation:
Tincture is prepared by using 2-7% elemental iodine and either of potassium iodide or sodium dissolved in alcohol. Since alcohol is a good solvent and iodine does not dissolve in water answer should be alcohol.
5. Which of the following are homogeneous in nature?
(i) ice
(ii) wood
(iii) soil
(iv) air
a. (i) and (iii)
b. (ii) and (iv)
c. (i) and (iv)
d. (iii) and (iv)
Soln:
Answer is (c) (i) and (iv)
Explanation
Air and ice are homogeneous mixture because its elements are not visible and cannot be distinguished from one another.
6. Which of the following are physical changes?
(i) Melting of iron metal
(ii) Rusting of iron
(iii) Bending of an iron rod
(iv) Drawing a wire of iron metal
(a) (i), (ii) and (iii)
(b) (i), (ii) and (iv)
(c) (i), (iii) and (iv)
(d) (ii), (iii) and (iv)
Soln:
Answer is (c) (i), (iii) and (iv)
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