pH Flashcards
pH scale…
expresses hydrogen ion (H+)
concentration in a solution.
– logarithmic scale ranging from 0-14
- neutral = 7
Henderson and Hasselbach decided to make it easier for
us and they came up with this:
pH = - Log10[H+]
pH is a measure of…
f [H+]
in aqueous solutions:
- Basic pH > 7
- neutral pH = 7
- acidic pH < 7
What kind of expression is pH?
a
logarithmic
expression
of [H+]
Acids:
dissociate in water to increase the
concentration of H+.
– pH values lower than 7
Bases:
combine with H+
ions when dissolved
in water, thus decreasing H+ concentration.
– pH values above 7
Buffers:
act as a reservoir for hydrogen ions,
donating or removing them from solution as
necessary.
Strong acid:
- completely ionized in
aqueous solution
– HCl, HBr, HI, HNO3, HClO4, and H2SO4
Strong base:
- completely ionized in
aqueous solution
– LiOH, NaOH, KOH, Ca(OH)2
, and Ba(OH)2
The pH of weak acids solutions can be
determined by…
by first calculating the [H+
], taking in
consideration the Ka;
Ka = [H+] x [A-] /
[HA]
pH = - log [H+]
- Alternatively, one can also use the Henderson-Hasselbach equation:
pH = pKa + log [A-] / [HA]
Strong acids completely ionize in…
water to release H+ and an anion;
Weak acids only partially ionize in water.
(Show EX; pg 92)
Notes:
1) Use caution with HClO4 and HNO3
. They can react explosively with
organics.
2) Strong acids can react quickly with proteins and triglyceride fats;
so be careful in using them. Always use eye protection.
Strong bases completely ionize in…
water to release OH- and a cation;
Weak bases only partially ionize in water.
(Show EX; pg 93)
Notes:
1) Bases react more quickly than acids with proteins and triglyceride fats;
so, be very careful in using them. Always use eye protection.
Ionization of Acids
Diagram pg 94
Ionization of Water:
In pure water a very few pairs of molecules
undergo the following reaction:
2 H2O ⇄ H3O(+) + OH(-)
Molarity of Water:
1 liter of water weighs 1000 g
1 mole of water = 18 g
Therefore the molarity of water is;
= 1000 /18
= 55.5 M
