Acids, Bases, and Buffers
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22 Terms
Complete the equilibrium and label the conjugate acid-base pairs.
Write balanced full equations and ionic equations for the following acid reaction
Write balanced full equations and ionic equations for the following acid reaction
Write balanced full equations and ionic equations for the following acid reaction
Strong Acids equations
When calculating the pH of strong monobasic acids, what assumptions do you make?
That the acid is full dissociated, so [H+] = [HA]
That water dissociation is negligible
Weak Acids equations
What’s the expression for the ionic product of water?
Strong Bases equations
Pure Water equations
Diluted Acid equations
Diluted Base equations
Buffer Solutions equations
Vertical parts of strong acid and strong base.
Strong acid steep between pH 4 – 7
Strong base steep between pH 7 – 10
No steep part for weak acid or base
“Strong acid – Strong base” pH curve
pH = 1
pH = 13
pH = 7
Volume at neutralisation = 25cm3
Steep between pH 4-10
“Strong acid - Weak base” pH curve
pH = 1
pH = 9
pH = Less than 7
Volume at neutralisation = 25cm3
Steep between pH 4-7
Half Neutralisation Volume for Weak Acids
Half neutralisation volume is the point in a titration where half of the weak acid (HA) has been neutralised by the base (OH-)
At half the neutralisation volume, [HA] = [A-]
Ka = [H+][A-] / [HA]
Since [HA] = [A-], they cancel out.
Ka = [H+]
pKa = pH
If we know the Ka, we can then work out the pH at 1/2 V
If a pH curve is plotted, then the pH of a weak acid at half neutralisation (1/2 V) will equal the pKa.
![<p>Half neutralisation volume is the point in a titration where half of the weak acid (HA) has been neutralised by the base (OH-)</p><p>At half the neutralisation volume, [HA] = [A<sup>-</sup>]</p><p></p><p>Ka = [H<sup>+</sup>][A<sup>-</sup>] / [HA]</p><p>Since [HA] = [A<sup>-</sup>], they cancel out.</p><p>Ka = [H<sup>+</sup>]</p><p>pKa = pH</p><p></p><ul><li><p>If we know the Ka, we can then work out the pH at 1/2 V</p></li><li><p>If a pH curve is plotted, then the pH of a weak acid at half neutralisation (1/2 V) will equal the pKa.</p></li></ul><p></p>](https://knowt-user-attachments.s3.amazonaws.com/42bcc4bc-114d-4d3f-a43e-70298d5314d9.png)
“Weak acid – Strong base” pH curve
pH = 3
pH = 13
pH = More than 7
Half neutralisation volume x2
Steep between pH 7-10
“Weak acid - Weak base” pH curve
pH = 3
pH = 9
No equivalence point
No volume at which equivalence occurs
No steep part of curve
Phenolphthalein
Only use in titrations with strong bases (NOT weak bases)
Colourless acid → pink alkali
Methyl orange
Only use in titrations with strong acids (NOT weak acids)
Red acid → yellow alkali
Enthalpy Change of Neutralisation