GCSE Chemistry- Chemical Changes (Acids, Alkalis, Bases)

year 9

Methyl Orange colour in acids

Red

Methyl Orange colour in Neutral

Orange

Methyl Orange Colour in Alkalis

Yellow

Phenolphthalein colour in Acidic

colourless

Phenolphthalein colour in neutral

colourless

Phenolphthalein colour in Alkalis

Pink

Acid

A substance with pH lower than 7 and produces H+ ions when dissolved in water.

Base

A substance with pH greater than 7

Alkali

A soluble base that releases OH- ions in solution

Indicator

Any substance that changed colour when it is added to acidic or alkaline solutions

Neutral

A solution with a pH of 7

How can pH be measured?

Using an indicator, pH meter or pH probe

What is the ionic equation of neutralisation?

H + OH = H20

Acid + Alkali =

Salt + Water

Acid + Metal =

Salt + Hydrogen

Acid + Metal Oxide =

Salt + Water

Acid + Metal Carbonate =

Salt + Water + Carbon Dioxide

Formula for Hydrochloric Acid

HCl

Formula for Sulfuric Acid

H2SO4

Formula for Nitric Acid

HNO3

Formula for Carbonic Acid

H2CO3

Formula for Phosphoric Acid

H3PO4

Salt derived from hydrochloric acid

Chloride

Salt derived from Sulfuric Acid

Sulfate

Salt derived from Nitric Acid

Nitrates

Salt derived from carbonic acid

carbonate

Salt derived from phosphoric acid

phosphate

Forming soluble salts from an insoluble base

1. gently warm dilute acid using a bunsen burner

2. add the insoluble base in excess to the acid until no more reacts

3. filter out the excess solid that hasn’t reacted

4. gently evaporate the solution using a water bath or bunsen burner to get pure crystals

Crystallisation

Heating a salt solution to evaporate, water, leaving behind pure salt crystals

What state symbol do acids always have?

Aqueous

Strong Acids

Completely ionised in solution, meaning that all the acid particles dissociate to release H+ ions into solution.

Weak Acids

Do not fully ionise in solution, meaning only a small proportion dissociate to release H+ ions

What does an acid’s STRENGTH tell you?

What proportion of the acid molecules ionise in water

What does an acid’s CONCENTRATION tell you?

How much acid there is in a certain volume of water

What would happen to the pH of an acid if it was mixed with water?

increase

What would happen to the pH of an acidic solution when more acid is added?

decrease

What does aqueous mean?

A solute dissolved in water