5.1.3 - Acids, Bases And Buffers Flashcards
What are acids?
Proton donors
What are bases?
Proton acceptors
What do H+ ions form in water?
Hydronium ions H3O+
What is the conjugate base?
The species that has lost a proton.
What is a conjugate acid?
Species that has gained a proton.
What are monoprotic acids?
Have only 1 proton they can release into solution.
Acid + alkali
Metal salt + Water
Acid + base
Metal salt + Water
Acid + carbonate
Metal salt + Water + Carbon dioxide
Acid + Metal
Metal salt + hydrogen
What is Ka used to calculate?
The concentration of a weak acid.
The higher the Ka?
The stronger the acid.
The lower the Ka?
The weaker the acid.
Ka =
[H+]^2 / [HA]
pKa =
-log Ka
ph =
-log[H+]
[H+] =
10^-pH
Kw =
[H+] x [OH-]
When a metal has a valency of 1 what does [OH-] =
[MOH]
If you are using a metal with a valency of 2, e.g. calcium what do you need to do to the value of [MOH] to find [OH-]?
Times by 2
What is a buffer?
A solution that as a system minimises pH changes on addition of small amounts of acid or base.
What 2 ways are buffers made?
- weak acid with the salt of its conjugate base.
- mix of an excess weak acid with a strong alkali.
In the buffer CH3COOH H+ + CH3COO- what happens when you increase H+ ?
The extra H+ ions combine with the CH3COO ions, causing the equilibrium to shift to the left reducing the concentration of H+.
In the buffer CH3COOH H+ + CH3COO- what happens when you increase OH- ?
OH- ions react with the H+ ions forming water, removing H+ ions. This causes CH3COOH to dissociate to form H+ ions # shifting the equilibrium to the right.
What does the pH in the blood need to be?
7.35 and 7.45
What is the pH in the blood controlled by?
Carbonic acid-hydrogen carbonate buffer system.
H2CO3 H+ + HCO3-
H2CO3 H2O + CO
How are levels of H2CO3 controlled in the body?
By respiration - by breathing out CO2 the level of H2CO3 is reduced as it moves this equilibrium to the right.
How are the levels HCO3- controlled?
The kidneys - they excrete extra in the urine.
How do you select an indicator for a titration?
The indicator just change colour over the narrow range that lies entirely on the vertical part of the pH curve.
What is the colour change from acid to alkali for methyl orange?
Red to yellow
What is the colour change from acid to alkali for phenolphthalein?
Colourless to pink.
What can indicators be though of as?
Weak acids as they have conjugate pairs.
