Question

Give reason why addition of zinc nitrate to water is a physical change but addition of zinc of dilute nitric acid is a chemical change

Answer 1

When Zinc nitrate is pored in the water it does not react with water.

It dissociates into the ions Zn⁺ and NO₃²⁻ .  No zinc hydroxide is formed.

Thus addition of Zinc nitrate into the water is a Physical change, as chemical properties of zinc nitrate in water remain as such.

While adding Zinc to dilute Nitric acid , we get

3Zn (s) + 8HNO₃ (dil) (l) →  3Zn(NO₃)₂ + 2NO+ 4H₂O

which is a Chemical reaction.Because zinc becomes zinc nitrate, besides producing nitrogen oxide and water.

Hope this helps...