A.
Choose the correct option.
1. In which of the following cases are the new substances formed?
b. Physical change
a Chemical change
d. Biological change
c. Periodic change
2. What happens when carbon dioxide is passed through lime water?
a. It turns milky
b. It becomes shiny
C. It turns grey
d. It turns golden yellow
3. Which of the following are reversible in nature?
a. Physical changes
b. Chemical changes
c. Biological changes
d. None of these
Which of the following is used to prevent rusting?
a. Galvanisation
b. Crystallisation
C. Amalgamating
d. Neutralisation
5. Which of the following is an example of irreversible chemical change?
a. Mixing salt in water
b. Melting of wax
C. Cutting of apple
d. Rusting of iron
Answers
1: options a (chemical change)
2: options a(It turns milky)
3: options c (Biological changes)
4: options d(Neutralisation)
5: options(Mixing salt in water)
Hi mate:
1. a) Chemical change
Reason:
Chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis.
2. a) It turns milky
Reason:
Resultant carbon dioxide passed through limewater in the right tube, producing a milky solution due to precipitation of the insoluble suspension of calcium carbonate:
Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O.
The milkiness disappears since calcium bicarbonate is water-soluble.
3. a) Physical change
Reason:
Processes such as melting, boiling, evaporation, freezing, condensation, dissolution are reversible changes.
4. a) Galvanisation
Reason:
The most common example of cathodic protection is the coating of iron alloy steel with zinc, a process known as galvanizing .
5. b) burning of wax.
Reason:
In the process of burning of wax, it is neither the solid wax nor the liquid wax that is burnt. Wax vapours are burnt giving off heat and light. Once burned, it is not possible to get back the wax. Burning of wax is a chemical process and hence, is irreversible.