Acids and Bases
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What is the definition of a Bronsted-Lowry acid?
A proton donor
What is the definition of a Bronsted-Lowry base?
A proton acceptor
How do you calculate the pH? (Using [H+])
pH = -log [H+]
How can you use the concentration of H+ ions to work out pH?
pH = -log(H+)
HX –> H+ + X- State whether this is a strong or weak acid, and give a reason why
Strong DIssociates completely
How do you calibrate a pH meter?
Rinse probe thoroughly with deionised water, and shake gently to remove excess Place probe in standard soln. of 4.00pH and record Repeat process using standard ph 7.00 and 9.20 buffer soln. Plot a graph of recorded pH (x) vs pH of buffer soln. (y) Can be used to convert experimental readings into more accurate ones
What is Kw?
The ionic product of water Kw = [H+][OH-] (x^2) = 1.00 x 10-14 mol^2dm^-6
How do you work out the acid dissociation constant?
Ka = [H+][X-] / [HX]
How do you work out pKa?
pKa = -logKa
Describe step-by-step how you would work out the pH if it was strong acid vs strong base, and the acid was in excess
1) find moles of acid 2) find moles of base 3) which is in excess? ACID IN XS calculate conc. of [H+] calculate pH using [H+]
Describe step-by-step how you would work out the pH if it was strong acid vs strong base, and the base was in excess
1) find moles of acid 2) find moles of base 3) which is in excess? BASE IN XS calculate [OH-] use Kw to calculate [H+] calculate pH using [H+]
Describe step-by-step how you would work out the pH if it was weak acid vs strong base, and the acid was in excess
1) find moles of acid mole of base XS –> ACID calculate moles of HA left and A- formed [HA]+[A-] (not always nec.) calculate [H+] conc using Ka calculate pH from [H+]
Describe step-by-step how you would work out the pH if it was weak acid vs strong base, and the base was in excess
mol of acid mol of base XS? –> BASE calculate [OH-] use Kw to calculate [H+] calculate pH using [H+]
What does acidic buffer contain?
A weak acid and the salt of that weak acid
What does basic buffer contain?
A weak base and the salt of that weak base
What is a buffer?
A solution that maintains an approximately constant pH, despite dilution or addition of small amounts of acid or base.
How does adding acid affect an acidic buffer?
A- + H+ –> HA Salt ions ‘mop up’ added H+
How does adding a base affect an acidic buffer?
HA + OH- –> A- H2O The acid (HA) can ‘mop up’ the added OH-
How does adding a base affect a basic buffer?
NH4+ + OH- –> NH3 + H2O Salt can ‘mop up’ added OH-
How does adding an acid affect a basic buffer?
NH3 + H+ –> NH4+ Eqm shifts to right Weak base ‘mops up’ added H+
What is the definition of an Arrhenius acid?
Any substance that adds H+ to water
What is the definition of an Arrhenius base?
Any substance that adds OH- to water
Where is the neutralisation points of titration curves for different combinations of acids and bases?
