Chemistry- Topic 3 Chemical Changes (Acids+ Alkalis) Summer Term Y9

what pH is acid

7 and under

what pH is alkali

7 and above

what pH is neutral

pH 7

Acid Indicators

• Red in UNIVERSAL

• Red in LITMUS

• Red in METHYL ORANGE

• Colourless in PHENOLPHALEIN

Alkali Indicators

• Purple in UNIVERSAL

• Blue in LITMUS

• Yellow in METHYL ORANGE

• Pink in PHENOLPHALIEN

Acids in solution produce…

Hydrogen ions (H⁺)

• hydrochloric acid - HCl

• sulfuric acid

• Nitric acid

Alkalis in solution produce…

hydroxide ions (OH^-)

• sodium hydroxide

• potassium hydroxide

what do stronger acids have

a higher concentration of hydrogen ions because they have fully dissociated to release ions

are alkalis soluble

alkalis are soluble bases

neutralisation reaction

a reaction between and acid and a base

Acid / Alkali Neutralisation Reaction

reaction when hydrogen ions from the acid react with hydroxide ions from the alkali to form water

Base

-all metal oxides are bases

-soluble bases are alkali (but not all bases are alkali)

salt

when hydrogen ions are replaced by positive ions (cations)

CORE PRACTICAL - Investigating Neutralisation

calcium hydroxide+ hydrochloric acid → calcium chloride + water

• 0.3 g calcium hydroxide is continually added to 50 ml of hydrochloric acid and the pH is tested

• there will be a sudden change around neutral (7)

Acid + Metal

Acid + Metal → Salt + Hydrogen

test for hydrogen

light a splint over and there will be a squeaky pop if present

Acid + Metal Carbonate

Acid + Metal Carbonate → Salt + water + carbon dioxide

test for carbon dioxide

by bubbling it through lime juice which will turn cloudy if present

CORE PRACTICAL - Preparing Copper Sulfate

sulfuric acid + copper (ll) oxide → copper (ll) sulfate + water

• a water bath is used to speed up reaction between acid and base

ionic equation for neutralisation (simplified)

H⁺ + OH⁻ → H₂O

Titration

used to prepare a SOLUBLE SALT from a reaction between an acid and alkali

Indicators suitable for Titration

-Methyl Orange

-Phenolphthalein

Titration method (summary)

1. Measure ALKALI with a volumetric pippete and add to conical flask along with INDICATOR

2. Fill Burrette with acid and add to the alkali slowly

3. Stop when indicator changes colour

4. Repeat for accuracy