topic 3 - acids and bases Flashcards
pH scale
a measure of how acidic or alkaline a substance is
acido
a substance with a pH of less than 7
they form H+ ions in water
the greater the concentration of H+ ions…
the lower the pH
base
a substance that reacts with an acid to form a salt and water
alkali
a soluble base
a substance with a pH of more than 7
forms OH- ions in the water
the greater the concentration of OH- ions…
the higher the pH
what are 3 examples of indicators
litmus
methyl orange
phenolphthalein
what colour is litmus in acidic, neutral and alkaline conditions
acidic - red
neutral - purple
alkaline - blue
what colour is methyl orange in acidic, neutral and alkaline conditions
acidic - red
neutral - yellow
alkaline - yellow
what colour is phenolphthalein in acidic, neutral and alkaline conditions
acidic - colourless
neutral - colourless
alkaline - pink
dissociation/ionisation of acid
splitting up to produce a hydrogen ion and another ion
acid strength indicated what
what proportion of the acid molecules ionise in water
strong acid features and examples (4)
- ionises almost completely in water
- large proportion of acid molecules dissociate to produce H+ ions
- pH 0-2
- nitric, sulfuric, hydrochloric
weak acid features and examples (4)
- doesn’t fully ionise in solution
- small proportion of acid molecules dissociate to produce H+ ions
- pH 2-6
- citric, ethanoic, carbonic
acid concentration
how much acid there is in a litre (dm^3) of water
measure in g/dm^3 or mol/dm^3
concentrated acid
has large amounts of acid molecules compared to the volume of water
dilute acid
has small amounts of acid molecules compared to the volume of water
if H+ ion concentration increases by a factor of 10…
the pH decreases by 1
acid + metal ->
acid + metal -> salt + hydrogen
test for hydrogen
test for hydrogen with a lit splint
the splint will burn with a squeaky pop if present
acid + metal carbonate ->
acid + metal carbonate -> salt + water + carbon dioxide
test for carbon dioxide
using limewater
if present, the limewater will turn cloudy
acid + metal hydroxide ->
acid + metal hydroxide -> salt + water
acid + metal oxide ->
acid + metal oxide -> salt + water
neutralisation reaction
a reaction between an acid and a base
describe the core practical to investigate neutralisation using calcium oxide and hydrochloric acid (6)
1) measure a set volume of hydrochloric acid into a conical flask using a pipette or measuring cylinder
2) measure a fixed mass of calcium oxide using a mass balance
3) add calcium oxide to hydrochloric acid
4) wait for the base to finish reacting and then record pH using a pH probe or universal indicator paper
5) repeat adding calcium oxide until the acid has fully reacted (which you know as there will be solid left at the flask’s base)
6) plot a graph to see how pH changes
common sodium, ammonium, potassium salts (solubility rules)
soluble
nitrates (solubility rules)
soluble
common chlorides (solubility rules) and exceptions
soluble
excluding silver and lead chlorides
common sulfates (solubility rules) and exceptions
soluble
excluding lead, barium and calcium
common carbonates or hydroxides (solubility rules) and exceptions
insoluble
excluding sodium, ammonium and potassium
how do you prepare an insoluble salt (simple)
done by precipitation reaction
react two soluble salts together
how do you prepare an insoluble salt (method) (6)
1) add a spatula of soluble salt to a test tube and dissolve in deionised water ; shake thoroughly to ensure salt is dissolved
2) repeat with a second soluble salt
3) tip the two solutions into a beaker and stir with a stirring rod
4) use filter paper to filter the precipitate out
5) wash the filtrate with deionised water
6) scrape onto fresh filter paper and leave to dry in an iron or desiccator
what are the 2 ways you can prepare a soluble salt
using an acid and an insoluble base
using an acid and a soluble reactant
how do you prepare a soluble salt using an acid and an insoluble base (6)
1) heat acid in a water bath in a fume cupboard
2) add the base to the acid in excess to ensure the acid has fully reacted
3) filter off excess solid so that only salt and water remain
4) heat solution gently to evaporate off some of the water
5) leave solution to cool and allow salt to crystallise
6) filter off solid salt and allow to dry
what method should you use to produce hydrated copper sulfate
acid + insoluble base method
with copper oxide and sulfuric acid
reaction of copper oxide and sulfuric acid to produce hydrated copper sulfate (product and equation) (describe product)
once the solution has crystallised, you will be left with blue crystals
CuO (s) + H2SO4 (aq) -> CuSO4 (aq) + H2O (l)
how do you prepare a soluble salt using an acid and a soluble reactant (simple and reason)
using an acid-alkali titration
this is because you need to work out exactly the right amount of acid needed to neutralise the alkali
how do you prepare a soluble salt using an acid and a soluble reactant (method) (8)
1) measure out set amount of acid to conical flask using a pipette
2) add a few drops of indicator with a single colour change
3) slowly add alkali to acid using burette until you reach the end point
4) carry out reaction again using identical volumes of acid and alkali but without indicator to prevent contamination
5) the solution that remains is only salt and water
6) evaporate water off slowly
7) leave salt to crystallise
8) filter off salt and allow to dry into a pure, dry salt
end point
the point during a titration when an indicator shows that the amount of reactant necessary for a complete reaction has been added to a solution
