C4 - Chemical Changes Flashcards
What is an acid?
it releases H+ (hydrogen) ions in water and turns universal indicator red - yellow
What is an alkali?
it releases OH- (hydroxide) ions in water and turns universal indicator blue - purple
metal + acid –>
salt + hydrogen
acid + alkali –>
salt + water
acid + carbonate –>
salt + water + carbon dioxide
What is the salt ending for hydrochloric acid?
chloride
What is the salt ending for sulfuric acid?
sulfate
What is the salt ending for nitric acid?
nitrate
When it ends in hydroxide, this means it’s …
an alkali
How do you test if a metal + acid reaction is successful?
Hydrogen test - lit splint, squeaky pop if positive
How do you test if an acid + alkali reaction is successful?
Universal indicator, turns green if positive
How do you test if an acid + carbonate reaction is successful?
Carbon dioxide test - lime water, turns cloudy if positive
Define independent variable
the thing you change in the experiment
Define dependent variable
the thing you measure
Define control variables
the things you keep the same (to ensure a fair test)
Define a strong acid
they fully ionise in water
Define a weak acid
they partially ionise in water
Describe a method a student could use to make pure dry crystals of salt from metal oxide and acid (6 marks)
- put 50 ml of (specific) acid in a beaker
- add excess amount of (metal) oxide to acid
- heat mixture using bunsen burner and stir
- filter mixture with funnel and filter paper to remove excess (metal) oxide
- heat (specific mixture) solution using a bunsen burner, evaporating basin and water bath for 10 mins
- leave to cool and crystallise
What is the ionic equation for neutralisation?
H+ + OH- –> H₂O
What colour does methyl orange turn for acid and alkali?
acid = red
alkali = yellow
What does a burette measure?
a burette is used to accurately measure a variable (unknown) volume drop by drop
What does a pipette measure?
a pipette measures a fixed volume
How do you do a titration calculation question?
- make a table for acid and alkali with n, c and v
- fill in what the question tells you (3 things)
- convert all volumes into dm³
- calculate the moles of the side you can - n = c x v
- use the molar ratio from the equation to find the other moles
- calculate the last missing space c = n/v
- to convert to g/dm³, times the answer by it’s relative formula mass
Define a dilute solution
small number of acid molecules per volume
Define a concentrated solution
large number of acid molecules per volume
Why can’t universal indicator be used during a titration experiment?
It doesn’t have a sudden change so end point is hard to determine
Define a displacement reaction
the metal in a compound is displaced by a more reactive metal to form a new compound
Define reduced (in terms of oxygen)
oxygen removed
Define oxidised (in terms of oxygen)
oxygen gained
Define electrolysis
electrolysis uses electricity to split ionic compounds
What happens at the cathode of a molten electrolysis?
- (metal) ion is attracted to the negative cathode
- (metal) ion gains (amount of positive charge it has) electrons to form a neutral atom
- (metal) has been reduced
What happens at the anode of a molten electrolysis?
- (non-metal) ion is attracted to the positive anode
- (non-metal) ion loses (amount of negative charge it has) electrons to form a neutral atom
- (non-metal) has been oxidised
- 2 atoms join to form a diatomic molecule
Describe an electrolysis diagram
There’s a cell with two electrodes - anode (+) and cathode (-). At the anode, there are anions which are negative non-metal ions and at the cathode, there are cations which are positive metal ions.
Define oxidation (in terms of electrons)
loss of electrons
Define reduction (in terms of electrons)
gain of electrons
What does the half equation look like at the negative electrode?
metal ion + electrons –> metal
- the amount of positive charge the ion has is the number of electrons
What does the half equation look like at the positive electrode?
non-metal ion –> electrons + non-metal (diatomic molecule)
- the amount of negative charge has to balance out as well as the number of molecules
Why does the ionic compound have to be molten/in solution for electrolysis?
so the ions can flow through the structure
Why is cryolite used in electrolysis?
It lowers the the melting point so it uses less energy to make molten.
Why does the positive electrode need to be replaced regularly (in aqeous electrolysis) ?
It is made of carbon which reacts with the oxygen produced at the anode to make carbon dioxide.
What are the two rules for electrolysis of an aqueous solution?
- at the negative electrode, the least reactive between hydrogen and the metal in the compound will form
- at the positive electrode, if it’s group 7 then it will be formed but if not, oxygen will form
What are the two extra ions involved in aqueous electrolysis?
H+ and OH- (because it was dissolved in water)
