F4chem一問

(i) Physical change
Air is a mixture containing oxygen and nitrogen. When oxygen and nitrogen is separated from air, no new substance is formed. Therefore, it is a physical change.

(ii) Physical change
When sugar is dissolved in water, a solution is formed. The solution contains the sugar and water, but no new substance is formed. Therefore, it is a physical change.

(iii) Chemical change
When the glowing splint relights, the wood of the splint is burned to give carbon dioxide and water. Since new substances (carbon dioxide and water) are formed, it is thus a chemical change.

(iv) Physical change
Sea water is a mixture containing mainly water and common salt. When salt is separated from sea water, no new substance is formed. Therefore, it is a physical change.

(v) Physical change
Sea water is a mixture containing mainly water and common salt. Similarly, when water is isolated from sea water, no new substance is formed. Therefore, it is a physical change.

(vi) Electrolyse water
When water (usually acidified) is electrolysed, hydrogen gas and oxygen gas are formed. Since new substances (hydrogen gas and oxygen gas) are formed, it is thus a chemical change.
=

Physical change既feature 係只會改變substance 既「外形」，唔會create 一啲既野出黎，所以要分係physical 定chemical 就要睇有冇野係產生出黎。

(i)Separate oxygen and nitrogen from air
Physical change
> 純粹separate, 無任何野create
(ii)Dissolve sugar intp water
Physical change
> Same
(iii)Relight a glowing splint in oxygen
Physical change
> 呢個我唔係好肯定... 基本上呢個係個test...但我覺得係physical...
(iv)Extract common salt from sea water
Physical change
> Same
(v)Isolate pure water from sea water
Physical change
> Same
(vi)Electrolyse water
chemical change
> 電解我地未教= =

希望我可以幫到你啦:D