Acids and Bases Flashcards
Define an acid
Proton Donor
Define a base
Proton Acceptor
Define a strong Acid
An acid (proton donor) which fully dissociates
Define a weak Acid
An acid ( proton donor) which only partially dissociates
Define pH
pH = -Log10[H+]
[H+] =
[H+] = 10-pH
Ionic Product of Water (Kw) =
Kw = [H+][OH-]
When calculating the pH of a strong acid use:
pH = -Log10[H+]
When calculating the pH of a strong base use:
Rearrange Kw = [H+][OH-] to get [OH-] then use pH = -Log10[H+]
When calculating the pH of a weak acid use:
Ka = [H+]2/[HA] and rearrange to get [H+]
then use pH = -Log10[H+]
When calculating the pH of a buffer use:
Ka = [H+][A-]/ [HA] and rearrange to get [H+] then use pH = -Log10[H+]
Chemical equation for Hydrochloric Acid + Sodium
HCl(aq) + Na(s) –> NaCl(aq) + ½ H2(g)
Chemical equation for Nitric Acid + Potassium Oxide
2HNO3 (aq) + K2O(s) –> 2KNO3 (aq) + H2O(l)
Chemical equation for Phosphoric Acid + Sodium Hydroxide
H3PO4(aq) + 3NaOH(s) –> Na3PO4(aq (aq) + 3H2O(l)
Chemical equation for Hydrochloric Acid + Calcium Oxide
2HCl (aq) + CuO(s) –> CuCl2 (aq) + H2O(l)
Chemical equation for Sulfuric Acid + Sodium Carbonate
H2SO4(aq) + Na2CO3(s) –> Na2SO4(aq) + CO2(g) + H2O(l)
Na2O(s) + H2O(l) –> products and pH
2Na+(aq) + 2-OH(aq) pH 13-14
MgO(s) + H2O(l) –> products and pH
Mg(OH)2(aq) pH 9-10
P4O10(s) + 6H2O(l) –> products and pH
4H3PO4(aq) pH 0-1
SO2(g) + H2O(l) –> products and pH
H2SO3(aq) pH 2-3
SO3(g) + H2O(l) –> products and pH
H2SO4(aq) pH 0-1
A difference of 1 on the pH scale means
a 10x difference in [H+]
pKa =
-Log10Ka
Ka =
10-pKa
The value of Kw will alter with temperature, explain why pure water is always neutral
because [H+] = [-OH] at all times.
Define a buffer
A BUFFER is a solution which can resist changes in pH when a small amount of acid or base is added
What is an acid buffer made of
An ACIDIC BUFFER is made of a weak acid and a soluble salt of that acid. It maintains a pH below 7.
What is a basic buffer made of
A BASIC BUFFER is made of a weak BASE and a soluble salt of that BASE. It maintains a pH above 7.
Steps to get to pH in a buffer calculation when given concentration of weak acid CH3COOH, concentration of the salt CH3COONa and Ka value for weak acid.
sub values straight into Ka = [H+][ CH3COO]/[CH3COOH].
Rearrange to get [H+]
Use pH = -Log10[H+]
Steps to get to pH in a buffer calculation when given volume and conc of both the weak acid and a base, where the weak acid is in excess, Ka value also given
Complete ICE box
Find new moles of acid and the moles of the salt produced.
sub mole* values into Ka = [H+][CH3COO]/[CH3COOH]. *volumes would cancel out so moles can be used instead of conc
Rearrange to get [H+]
Use pH = -Log10[H+]
Steps to get to pH in a buffer calculation when enough base has been added to neutralise exactly half of the acid present.
Recognise this is a special situation - half neutralisation point so Ka = [H+]
Use pH = -Log10[H+]
Formula for sulphuric acid
H2SO4
Formula for nitric acid
HNO3
Formula for phosphoric acid
H3PO4
Formula for ethanoic acid
CH3COOH
Formula for aluminium phosphate
AlPO4
Formula for sodium ethanoate
CH3COONa
Formula for lead (II) nitrate
Pb(NO3)2
Formula for potassium sulphate
K2SO4
Formula for magnesium chloride
MgCl2
Explain how to chose a suitable indicator for a titration
A SUITABLE INDIATOR CHANGES COLOUR SOMEWHERE ON THE VERTICAL SECTION OF A pH TITRATION CURVE
Define half neutralisation point
‘The point at which enough base has been added to neutralise exactly half of the acid’
What does the vertical section of a titration curve show?
This indicates what the average titre would be which can be used in a calculation. The midpoint of this vertical section is the equivalence point.
