CATEGORY ： Chemistry 12 Base and Acid 01 2007/03/10 Sat TB ： CM ： 0 △

Describing Asids and Bases:

We can use an wquilibrium constant to find the concentrations of H₃O⁺ and OH^- in acid/base solutions.

This constant, Kw, is called the ion product constant for water. In general; Kw = [H₃O⁺][OH^-]

At 25℃, Kw = 1.0x10^-14

* If given the concentration of either H₃O⁺ or OH^-, we can find the missing concentration

EX: Find H₃O⁺ and OH^- in 0.45M HCl.


Using pH...

The range of [H₃O⁺] can be very large. To overcome this problem we work with logarithms.
pH can be defined as -log[HSUP>+] or pH = -log[H₃O⁺ ]

In neutral water at 25℃

[H₃O⁺] = 1.0 X 10^-7

pH = -log[H₃O⁺] = -log[1.0 X 10^-7] = 7



Similar to pH, we can also describe [OH^-] by using pOH:

pOH = -log[OH^-]

* Remember that;
Kw =[H₃O⁺] [OH^-] = 1.0 X 10^-14
taking -log of both sides....
= pH + pOH or pH + pOH = 14

A logarithm of number is the power to which you most raise 10 to equal that number.
We can also find [H₃O⁺] and [OH^-] by finding the antilog of this pH or pOH.

[H₃O⁺] = 10^-pH
[OH^-] = 10^-pOH

* on your culculator, use 10^x button!