Question

Which of the following changes are chemical? Which are physical?:
(1) dissolving sugar
(2) magnetizing a compass needle
(3) milk turning sour
a.
They are all physical changes
c.
(1) and (2) are chemical changes and (3) is physical
b.
They are all chemical changes
d.
(1) and (2) are physical changes and (3) is chemical

Answer 1

(1) : Dissolving sugar-> When dissolving sugar there is no chemical reaction as such, the sugar molecules just fit in with the water molecules, there is no bond breaking and bond formation. And through evaporation you can get back the sugar and condensation of the water vapour gives you back the water used. That is a characteristic of a physical change.

(2) Magnetizing a compass needle is a physical change. A realignment of groups of iron atoms takes place, but no real change within the iron atoms themselves occur.

(3) Both. Milk turns sour because the growth of bacteria in it. That makes a chemical change. while the sour turns to semi solid from liquid, so its a physical change

so its most likely
d.
(1) and (2) are physical changes and (3) is chemical