SIGNS OF CHEMICAL CHANGE—PRACTICAL EXERCISE
Aim: To observe signs of chemical change in a variety of reactions.
Recall:
Signs of chemical change include:
* A precipitate forming
* Heat released or absorbed
* Gas produced
* A permanent colour change
* Light produced
1. Carry out the following reactions and complete the table.
Experiment
Reactants
1
1 M hydrochloric acid (HCl(aq))
1 M sodium hydroxide (NaOH(aq))
Hydrochloric acid + sodium
hydroxide  sodium chloride + water
Place 10 mL of HCl(aq) in Ti = 19°C
a 100 mL beaker. Take the Tf = 23°C
temperature of the solution,
then add 10 mL of
NaOH(aq) and take the
temperature again.
Yes. Temperature
change.
2
0.1 M silver nitrate (AgNO3(aq))
0.1 M sodium chloride (NaCl(aq))
Silver nitrate + sodium chloride 
Silver chloride + sodium nitrate
Place 10 mL of NaCl(aq)
in a 100 mL beaker. Take
the temperature of the
solution, then add 10 mL
of AgNO3(aq) and take the
temperature again. Expose
the tube to UV light and
observe any changes.
Using tongs, hold a 4cm
strip of magnesium in a
Bunsen flame until it
ignites. Let it burn, then
drop it on the heat mat. DO
NOT STARE AT THE
FLAME!
White precipitate formed.
Ti = 18°C
Tf = 19°C
With UV light:
Turns grey and clumpy
Yes. Precipitate
forms. Heat
produced. Then,
permanent colour
change.
Very bright light, white
powder remains.
Yes. Light and heat
produced.
With UV
Silver chloride  silver + chloride
3
Magnesium (Mg(s))
Oxygen (in air) (O2(g))
Magnesium + oxygen 
Magnesium oxide
Instructions
Observations
Did a chemical change
occur? Explain.
4
Sodium carbonate (Na2CO3(s))
1 M Nitric acid (HNO3(aq))
Sodium carbonate + nitric acid 
sodium nitrate + carbon dioxide +
water
Place a spatula full of
sodium carbonate in a 100
mL beaker. Add 10 mL of
nitric acid. Record any
temperature changes.
Bubbling, solid dissolves. Yes. Gas produced,
Ti = 17°C
temperature change
Tf = 22°C
5
Flour and oxygen (in air)
Carbohydrate + oxygen  carbon
dioxide + water
Light a Bunsen burner.
Carefully sprinkle flour
over the Bunsen flame.
Flame expanded, turned
orange, sparks
Yes. Heat and light
produced.
6
Exhaled air
Limewater
Calcium hydroxide + carbon dioxide
 calcium carbonate + water
Using a straw and a small
beaker of limewater,
exhale into the limewater
until you see a change.
Limewater turned
cloudy.
Yes. Precipitate
formed.
7
Magnesium
1 M HCl
Magnesium + hydrochloric acid 
Magnesium chloride + hydrogen
Pop test
Hydrogen + oxygen  water
Place a small piece of
magnesium into a large test
tube with 10 mL of
hydrochloric acid. Use a
stopper to collect the gas.
Test it with a lit match.
Bubbling, magnesium
dissolved. Heat
produced.
With match: made
popping sound
Yes. Gas and heat
produced.
2. Write word equations for the reactions you observed.
Extension—write chemical equations for the reactions you observed.