Acuds and Bases Flashcards
(23 cards)
Two ways of measuring the ph of a solution
- Universal indicator
- Ph probe attached to a Ph meter
What are titrations used for
Titrations are used to work out how much of an acid is used to neutralise a base of unknown concentration. Or vice versa
What do titration curves used for
Titration curves are used to show where neutralisation happens during titration.
If you add acid to a base, the ph will decrease. What will happen if you add a base to an acid?
The ph will increase
What does the vertical point in the curve show
The vertical point in the curve shows where the neutralisation happens. This is called the end point of the titration
Method of titration (6 marker)
MAKE SURE YOU REVISE THIS
-Using a pipette, measure out a set volume of the alkali into a flat. Add a few drops of an indicator (usually phenolphthalein or methyl orange. You cannot use Universal indicator- it changes colour gradually and you want a single colour change)
-Fill a burette with a standard solution (a known concentration) of acid. Make sure to keep the burette below eye level whilst filling it you don’t want to look up during any acid spills
-Use the burette to add the acid to the alkali a bit at a time. Swirl the flask regularly. Go slowly (a drop at a time) when the alkali’s mostly neutralised
- This indicator changes colour when all the alkali has been neutralised- phenolphthalein is pink in alkalis but colourless in acids, and methyl orange is yellow in alkalis but red in acids
-record the volume of acid used to neutralise the alkali. This is called the titre.
- Repeat this process a few times, making sure you get very similar results each time. Then take the mean
what colour is phenolphthalein in acids and alkalis
It is pink in alkalis but colourless in acid
what colour is methyl orange in acid and alkalis
it is yellow in alkalis but red in acids
What do strong acids do?
Strong acids ionise almost completely in water. A large proportion of acid molecules dissociate to release H+ ions. There pH tends to be low from 0-2
Examples of strong acids
sulfuric acid, hydrochloric acid, and nitric acid
What do weak acids do
Weak acids don’t fully ionise in solution. Only a small proportion of acid molecule dissociate to release H+ ions. Their pHs tend to be around 2-6
What is Acid strength.
Acid strength tells you what proportion of acid molecules ionise in water
What is the concentration of acid
The concentration of acid measures how much acid there is in a litre of water. It is basically how much how watered down your acid is
What ion is released when acids dissolve in water
H+ ions
What ion is released when alkalis dissolve in water
OH- ions
What does changing the concentration of an acid do?
It changes the pH
what happens when the concentration of H+ ions increases by a factor of 10
the pH decreases by 1
Acid + metal ?
Salt and hydrogen are produced
What happens when you react a metal carbonate and an acid
It forms salt, water and Carbon dioxide
What happens when you react an acid and an alkali
It forms Salt and water
What salts do hydrochloric acid form
Chloride salts
For example Sodium chloride
what salts do sulfuric acid
They form sulfate salts
what salts do Nitric acid form
Nitric acid produces nitrate salts when neutralised but…
the reaction of nitric acid with metals is more complicated- you get a nitrate salt but instead of hydrogen gas, the other products are usually a mixture of water, NO or NO2
For example
HNO3+ Na —> NaOH + NO2
