Changes all around us
Articles made of iron rust when they are exposed to air. Camphor balls left exposed to air grow smaller. Ice melts and becomes liquid water.
All three are changes in matter. But are they changes of the same kind? Melt an ice cube and put it back in the freezer and you have ice again. A rusted nail, though, can never be turned back into a new one.
That is the question this chapter opens with
In some changes the substance remains itself — only its appearance or its state is different. In others, an entirely new substance comes into being.
How do we tell them apart?
Telling the two apart takes more than looking — it takes testing. Activity 16.1 has four parts, one of which belongs to the first kind and three to the second.
Activity 16.1 — what you need
A piece of magnesium (Mg) ribbon, about 50 ml of dilute sulphuric (H2SO4) acid solution, a few pellets of sodium hydroxide (NaOH), two metal spoons, a camphor ball (naphthalene), a box of matches, two 50 ml beakers, a Bunsen burner and a thermometer.
Over the next two pages we carry out the four parts one by one and compare the observations they give.