Lesson: Chapter 16 — Changes of Matter

16.1. Reactants and products 3 of 4

Four reactions to watch

Activity 16.2 contains four reactions — and those four belong to four different kinds. We meet all four again over the following pages.

Activity 16.2

1. Hold a piece of magnesium ribbon in tongs and put it into a burner flame.
2. Take a few crystals of potassium permanganate in a boiling tube and heat them. Meanwhile insert a glowing splint into the tube.
3. Take a little copper sulphate solution in a test tube and drop a clean piece of zinc strip into it.
4. Take a little barium chloride solution in a test tube and add a little sodium sulphate solution to it.

Table 16.2

Reaction	Nature of the reactants	Observation	Nature of the products
i. Burning magnesium (Mg)	A shiny silvery metal.	Burns with a brilliant white flame.	A white powder.
ii. Heating potassium permanganate	A purple crystal.	The glowing splint put into the tube bursts back into flame.	Two solids and a gas.
iii. Zinc into copper sulphate solution	A blue solution and a silvery metal.	The blue fades; a brown powder forms.	A colourless solution and a brown metal.
iv. Barium chloride + sodium sulphate	Two colourless solutions.	A white precipitate appears.	A white solid and a solution.

All four are chemical reactions

Burning with a flame, a gas given off, a change of colour and a precipitate — four of the signs listed on the previous page, one in each row.