Acids and Bases Flashcards
What is a Bronsted Lowry acid
A proton donnor
What is a Bronsted Lowry base
A proton acceptor
What does acid base equilibria involve?
The transfer of protons
Why do we use the log scale for hydrogen ion concentration
It covers a very wide range
What is the pH formula
pH = -log10[H+]
What is the kw formula used for?
Water and Strong bases
What is the Kw formula
Kw = [H+][OH-]
How does the value of kw vary
With temperature
How is Kw special for pure water
Kw = [H+]^2
How can water act?
As both an acid and a base.
It can lose or gain an H+
Why does the pH of water change with temperature
The forward reaction will be favoured, and more hydrogen ions and hydroxide ions will be formed. The effect of that is to increase the value of Kw as temperature increases.
How do weak acids and bases dissociate
Only slightly
What is the dissociation constant of a weak acid
Ka
What is pKa equal to
-log10Ka
What do we assume for weak acids
No dissociation
What does assuming no dissociation mean for a weak acid
[H+] = [A-]
This means making H+ squared instead of A- and H= separately
What is the formula for Ka
Ka = [H+] [A-]/
[HA]
How do you work out pH of a strong acid
Assume complete dissociation e.g. 0.16mol dm-3 of HCl
[H+] = 0.16
What does a graph of a strong acid and strong base look like
Low starting pH and high end pH.
Long equivalence point
What does a graph of a strong acid and weak base look like
Low starting pH and just above neutral end pH.
Short equivalence point
What does a graph of a weak acid and strong base look like
Starting pH not far below neutral and high end pH.
Short equivalence point
What does a graph of a weak acid and weak base look like
Starting pH not far below neutral and just above neutral end pH.
Very short equivalence point
What does a buffer pH do?
Maintains a constant pH
What do acidic buffers contain?
A weak acid and the salt of that weak acid
What do basic buffers contain?
A weak base and the salt of that weak base
What is the equivalence point?
Just enough acid has been added to neutralise the base or visa versa
What goes in an ice table
Moles
A buffer solution has a constant pH even when diluted. Use a mathematical expression to explain this.
