CH3.9 Acid-base equilibria Flashcards
concentrated
means that there’s a large amount of acid or base dissolved in a set volume of water
Dilute
means that there is a small aount of acid or base dissolved in a set volume of water
Lowrt-Bronsted definition
An acid is a substance that releases or provides H+ ions (H+ donar)
A base is a substance that removes or accepts H+ ions (H+ acceptor)
strong acid
Is one that almost totally dissociated (splits up) into H+ ions and negative ions in solution in water
A weak acid
is one that partially dissociates into H+ ions and negative ions in water. The free ions are in equilibrium with unidissociated acid molecules
ph of a weak acid
about 4
ph of a weak alkali
about 9
definition of pH
pH=-log(H+(aq)
what does one chagne in pH mean
a multilple of 10 e.g 10,100 ,, 1000, 100000
Ka equation for the equation Ha H+ + A-
Ka = (H+)(A-)/(HA)
kW equation
kW = (H+)(OH-)
kW at 25 degrees c
is approximately 10-14 mol^2dm^-6
buffers
resists chagne in pH as small amounts of alkali are added to a a acid or acid added to a alkali.
what is a buffer typically made up of
weak acid, a salt of the same acid with a strong base
when acid is added to the buffer
THe amount of H+ ions increases and this causes the equilibrium to shift to the lefft removing the H+ ions by reacting with the negative ion.
when alkali is added to a buffer
The amount of OH- ions is increase and this removes some of the H+ ions present. This causes the equilibrium to shift to the right producing H+ ions. The H+ ions replace those removed by reaction with the hydroxide ions.
buffers are used as (2)
- stoing enzymes to ensure pH remains at the optmum value
- storing of biological molecules, such as pharmacceuticals, which will be denatured at the incorrect pH
Henderson-Hasselbach equation
pHbuffer=pKa + log(SALT)/(ACID)
a salt produced from a stron acid and strong alkali will form …
neutral solutions
a salt produced from a strong acid and weak alkali will be …
an acidic salt
a salt produced by a weak acid and strong alkalie wil be a…
basic salt
vertical region on acid-base titration cuves
vertical region happens when the number of moles of alkali added equals the number of moles of acid in the original solution. This is calle
indicator
is a substance that has different colours in low and high pH solutions. This can be used to differentiate between an acid and an alkali but cannnot distiniguish between acids of different pH or alkali of differen pH
universal indicator
is a solution that shows a range of colours as the pH changes, so it can be used to find the pH of a particular solution.
phenolphthalien approximate colour chagne range
8.3-10.0
bromothylmol blue approximate colour change
6.0-7.5
Litumus approximate colour change
4.0-6.5
Methyl orange approximate colour change
3.2-4.4
