Chemical Changes Flashcards
What is an alkali
A base that is soluble in water where the concentration of OH- is high(er)
What colours does litmus go
Red in acidic solutions
Purple in neutral solutions
Blue in alkaline solutions
What colours does methyl orange go
Red in acidic solutions
Orange in neutral Yellow in alkaline solutions
What colours does phenolphalein go
Colourless in acidic or neutral solutions
Pink in alkaline solutions
What is reaction between an acid and base called
Neutralisation
What do strong acids do in water
Fully (or close to) dissociate
What do weak acids do in water
Partially dissociate
How much does pH increase by
A factor of 10
What forms when an acid reacts with a metal (hydr)oxide
Salt + water
What forms when an acid reacts with a metal
Salt + Hydrogen
What forms when an acid react with a metal carbonate
Salt + Water + Carbon dioxide
How to test for CO2
bubble the gas through limewater and if present the limewater will turn cloudy then colourless again
Solubility rules
All sodium, potassium and ammonium salts are soluble
All nitrates are soluble
Most chlorides (except silver and lead) are soluble
Most sulphates (except lead, barium and calcium) are soluble
Most carbonates and hydroxides (except sodium, potassium and ammonium) are insoluble
What happens when an acid reacts with ammonia
An ammonium salt is formed
How to to make an soluble salt from an insoluble base
Excess base method
This cannot be used to make sodium, potassium and ammonium salts
Excess base method
Use the metal oxide and corresponding acid
eg. to make copper sulfate crystals use copper oxide + sulfuric acid
Add some of the acid to a beaker and then add excess base to ensure that all of the acid has been used up
Gently warm
Filter then evaporate
What is the titration method used for
Making sodium, potassium and ammonium salts which are inseparable by filtration
Titration method
Choose suitable chemicals
Alkaline + corresponding acid (similar to excess base)
Use glass pipette to place 25.0 cm ^3 of alkali into a conical flask
Add a few drops of phenolphthalein (it will turn pink)
Put the acid into the burette and add to the alkali a bit at a time + swirl
Measure where indicator goes colourless
Repeat and be careful + adjust volume
Heat the mixture and evaporate water
Leave to crystallise
Filter
What is the precipitation method used for
To make insoluble salts and when both base and salt are solids
Precipitation method
Use the metal nitrate and the sodium compound
eg. Barium nitrate and sodium sulfate to make barium sulfate
Mix the two solutions together in a beaker
Filter
Wash with distilled water
Leave to dry
What is a precipitate
A solid made from reacting two solutions together
What happens to the cations in electrolysis
reduction
What happens to the anions in electrolysis
oxidised
How to set up an electrochemical cell
2 inert electrodes (usually graphite)
Clean the surfaces using emery paper
Place into a beaker
Connect to a power supply using crocodile clips and wires
What is formed at the cathode
Hydrogen gas
OR
If less reactive metal than hydrogen is present that will be formed
What is formed at the anode
Oxygen
OR
Halides if they are present
What is the half-equation at the anode is oxygen is formed
4OH- –> O2 + 2H2O +4e-
