Physical and Chemical Changes — Question 9
Back to all questionsQuestion 9
State why addition of sodium chloride to water is considered a physical change, while addition of dilute sulphuric acid to zinc is considered a chemical change.
Addition of sodium chloride (salt) to water is considered a physical change because:
(a) It is a temporary and reversible change. On adding, the salt dissolves in water and forms a salt solution. On evaporation of the salt solution the original salt remains behind. Hence, it is a reversible change.
(b) No new substances are formed. Original and the final product is the same [NaCl].
Addition of dilute sulphuric acid to zinc is a chemical change because :
Zinc + dil. Sulphuric Acid ⟶ Zinc Sulphate + Hydrogen gas
(a) It is a permanent and irreversible change.
(b) New substances zinc sulphate and hydrogen gas are formed.