At 318K Kw is 4.02x10-14 calculate the pH of water?
-log(√4.02x10-14 = 6.70
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What equation would you use to go about calculating the pH of a strong base using Kw?
[H+]= Kw divided by [OH-]
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Calculate the pH of 0.1 moldm3 of NaOH?
-log(1x10-14 divided by 0.1 = 13.00
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What is the Ka expression for a weak acid?
Ka= [H+][A-] divided by [HA]
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What is the simplified Ka expression for a weak acid?
Ka= [H+]2 divided by [HA]
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How would you calculate [H+] for a weak acid from Ka?
[H+]= √Ka x [HA]
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Calculate the pH of 0.1moldm-3 of chloroethanoic acid with a Ka of 1.38x10-3?
-log(√0.1 x 1.38x10-3 = 1.93
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What is the expression for pKa?
pKa= -logKa
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How would you get Ka from pKa?
10-pKa
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How would you calculate the [H+] from diluting a strong acid?
[H+]old x (old volume divided by new volume)
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How would you calculate the [OH-] from diluting a strong base?
[OH-]old x (old volume divided by new volume)
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Calculate the pH when 100cm3 of H20 is added to 25cm3 of 0.5moldm-3 of KOH?
0.5 x (25/100+25) = 1x10-14/0.10 = 13.00
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What is an example of a strong acid?
HCl
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What is an example of a strong base?
NaOH
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What is an example of a weak acid?
Ch3COOH
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What is an example of a weak base?
NH3
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What can't methylorange be used for?
A weak acid
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What pH range does methylorange have?
3.1-4.4
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What can't phenolphthalein be used for?
A weak base
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What pH range does phenolphthalein have?
8.3-10
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How would you know if the question was a strong acid/base question?
The Ka isn't given
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How would you go about calculating a strong acid question?
Balance eqauation, Work out initial moles, find out remaining moles, divide by total volume, then -log
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How would you go about answering a strong base question?
Balance equation, work out initial moles, find remaining moles, divide by total volume, divide by Kw (1x1o-14) and then -log
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How would you know the question is a weak acid question?
The Ka is given
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What is the Ka expression for a weak acid?
Ka= [H+]2/[HA]
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How would you calculate [H+] from Ka in a weak acid question?
[H+] = √Ka x [HA]
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How would you go about answering a weak acid question?
Find out original moles, find out which is in excess - if acid proceed, take away to find remaining, divide moles by salt (limiting factor), times by Ka and then -log
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What do you do in a weak acid question if the base is in excess?
Answer it as if it was a strong base question
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How do you know it's a buffer question?
The ka is given
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What is the Ka expression for a buffer question?
Ka= [H+][X-]/[HX]
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How would you find [H+] in a buffer question?
[H+]= Ka x acid/salt
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How would you go about answering a buffer question?
Find out original moles, calculate moles remaining, times by Ka, take away from salt/smallest number and then -log
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