Reactions

Question 1

Testing pH: Litmus

Answer 1

ACIDIC - red
NEUTRAL - purple
ALKALINE - blue
Good because it changes colour around pH 7 so you can confidently say whether it is acid or alkaline.

Question 2

Testing pH: Phenolphthalein

Answer 2

ACIDIC - colourless
NEUTRAL - none (sudden change)
ALKALINE - pink
Changes around pH 9, which doesn’t matter as long as you are testing strong acids or alkalis.

Question 3

Testing pH: Methyl orange

Answer 3

ACIDIC - red
NEUTRAL - none (sudden change)
ALKALINE - yellow
Changes around pH 4, used in titration.

Question 4

Testing pH: Universal indicator

Answer 4

ACIDIC - red
NEUTRAL - green
ALKALINE - blue
Measures pH 1-14 but isn’t very accurate.

Question 5

Acid + metal ->

Answer 5

ACID + METAL -> SALT + HYDROGEN

Dilute sulfuric acid + metal -> Metal sulfate + hydrogen

Question 6

Acid + metal oxide ->

Answer 6

ACID + METAL OXIDE -> SALT + WATER

Dilute sulfuric acid + metal oxide -> Metal sulfate + water

Question 7

Acid + metal hydroxide ->

Answer 7

ACID + METAL HYDROXIDE -> SALT + WATER

Dilute hydrochloric acid + metal hydroxide -> Metal chloride + water

Question 8

Acis + metal carbonate ->

Answer 8

ACID + METAL CARBONATE -> SALT + CARBON DIOXIDE + WATER

Dilute nitric acid + metal carbonate -> Metal nitrate + carbon dioxide + water

Question 9

Redox reactions: Combination/ Synthesis reactions

Answer 9

Where two or more substances react to form just one compound.

IRON + SULFUR -> IRON SULFIDE

Question 10

Redox reactions: Decomposition reactions

Answer 10

Where a substance breaks down into simple structures, by LIGHT, HEAT, ENZYMES OR ELECTRICITY (for ionic substances- Lithium chloride -> Lithium + Chloride)

Question 11

Redox reactions: Combustion reactions

Answer 11

Where a substance catches fire and burns on reaction with oxygen (or another gas).
Reaction produces HEAT, LIGHT and SOUND.

MAGNESIUM + OXYGEN -> MAGNESIUM OXIDE

Question 12

Redox reactions: Displacement reactions

Answer 12

Where an element swaps place with a different element in a compound according to their place in the reactivity series.

COPPER + SILVER NITRATE -> COPPER NITRATE + SILVER

Question 13

Displacement reactions to find the reactivity series

Answer 13

Any metal higher in the series will displace one lower down from a compound when heated together.

Question 14

Neutralisation reactions

Answer 14

Where an acid reacts with another base that destroys its reactivity, giving water as a product.

SODIUM HYDROXIDE + HYDROCHLORIC ACID -> SODIUM CHLORIDE + WATER

Question 15

Precipitation reactions

Answer 15

Where solutions react, giving an insoluble product. Ions come together to form a solid but no electrons are transferred.

SILVER NITRATE + SODIUM CHLORIDE -> SILVER CHLORIDE (insoluble salt) + SODIUM NITRATE

Question 16

Making soluble salts (never sodium, potassium or ammonium salts)

Answer 16

• Acid + metal (only for metals between Mg and Fe in the reactivity series)
• Acid + metal oxide/ hydroxide
• Acid + carbonate

Question 17

Recrystallisation

Answer 17

Used to purify soluble substances contaminated with small quantities of other soluble substances.

1) Impure solid dissolved in minimum amount of hot water (or solvent)
2) Allowed to cool
3) Crystals are formed
4) They can be filtered and washed on the filter paper and then allowed to dry