Ionic Product for Water and pH of Water Flashcards
1
Q
What is the expression for Kc in water?
A
Kc = [H+] [OH-] / [H20]
2
Q
What is the expression for Kw in water?
A
Kw = [H+] [OH-]
3
Q
What is the value of Kw at 25 degrees celcius?
A
Kw = 10^-14 mol^2dm^-6
4
Q
Why is pure water neutral and what are the shortcuts regarding this rule, linked with the Kw expression?
A
Because [OH-] = [H+]
When neutral, Kw = [H+]^2
and so [H+] = root Kw
At 25 degrees celsius, [H+] = root 1^-14 so pH = 7.
5
Q
How does temperature affect the pH of water?
A
Dissociation of water is endothermic, so higher temperatures shift equilibrium to the right giving higher concentration of H+ ions, so a lower pH.
6
Q
pH table
A
7
Q
Why is the concentration of H+ in a diprotic strong acid not the same as the concentration of the acid?
A
- It is not fully ionised
- Happens in 2 steps, and the 2nd step suppresses the abundance of H+ from the first step creating equilibrium
- So the H+ concentration is less than double the acid concentration
