Topic 3 - Chemical Changes

Phenolphtalein acid to alkali

colourless to pink

Litmus paper acid to alkali

red to blue

methyl orange acid to alkali

red to yellow

relationship between hydrogen ions and pH

as hydrogen ions increase by a factor of 10, the pH decreases by 1

strong acids vs weak acids

strong acids dissociate fully into ions in solutions and release H+ ions. weak acids partilly dissociate into ions and only a few molecules release H+ ions

base + acid reaction

base + acid → salt + water

metal + acid reaction

metal + acid → salt + hydrogen

metal carbonate + acid reaction

metal carbonate + acid → salt + water + carbon dioxide

metal oxide or hydroxide + acid reaction

metal (hydr)oxide + acid → salt + water

chemical test for hydrogen

light splint ignites hydrogen with a squeaky pop

chemical test for carbon dioxide

bubble through limewater, turns cloudy

neutralisation reaction

reaction between an acid an a base

H+ + OH- → H2O

how to prepare insoluble salts

Mix solutions of two soluble salts

Filter the mixture

Wash the insoluble salt with distilled water

Dry the salt with filter paper or an oven

sodium potassium ammonium solubility

always soluble

nitrate solubility

always soluble

chloride solubility

always soluble except lead and silver

sulfates solubility

soluble except lead and barium

carbonates and hydroxides

insoluble (except sodium potassium and ammonium)

titration steps

Put acid into a burette

Use a pipette to put a known volume of alkali into a conical flask

Put a few drops of a suitale indicator (phenolphtalein) into the alkali

Record the burette start reading

Add acid to the alkali until the colour cahnges from pink to colourless

Record the burette end reading

electrolysis

electrical energy decomposes an electrolyte into its elements

cathode electrolysis

hydrogen is always produced unless the compound contains cations which are less reactive than hydrogen

anode electrolysis

oxygen is always produced unless the compound contains halide ions in which case chlorine, bromine or iodine are produced

cations in electrolysis

go to cathode. positively charged ions gain electrrons and are reduced

anions in electrolysis

go to anode, lose electrons and are oxidised

electrolysis for copper

Use a pure copper cathode, and an impure copper anode. Copper ions move to the copper electrodes, are discharged and form pure copper. Sludge form below the anode from impurities,