Determining pH and Kw

1. pH is a measure of how acidic or basic a substance is.
2. It is a scale which ranges from 0 (most acidic) to 14 (most alkaline).
3. The "pX" function of something stands for the "-log( X)", so pH actually stands for
   the -log([H⁺¹]). You should have seen this relationship in the serial dilution lab.
4. Neutral water has a pH of 7. That implies that there must be some H⁺¹ ions in pure water. Where might these ions come from?
5. Water, in fact, ionizes in an equilibrium reaction as follows: H₂O_(l) H⁺¹_(aq) + OH^-1_(aq)
   1. We can determine the hydrogen ion concentration in water from measuring its pH.
   2. Pure water has pH = 7. That means the [H⁺¹] = 1.0 x 10^-7 M
   3. Because you get one OH^-1 for each H⁺¹ the [OH^-1] = 1.0 x 10^-7 M
   4. Therefore Kw = [H⁺¹][OH^-1] = 1.0 x 10^-14 M
6. By adding acids to water you are actually disturbing the equilibrium. As more H⁺¹ ions are dissolved the equilibrium shifts left and consumes hydroxide ions. If a base is added, then the equilibrium will again shift to the left consuming H⁺¹. That is how a base lowers the pH value. If the H⁺¹ concentration decreases then the pH increases (becomes more alkaline).
   1. Practice calculations:
      1. What would be the pH of a solution with [H⁺¹] = 0.025 M?
      2. What would be the pH of a solution with [OH^-1] = 0.025 M?
      3. What would be the [H⁺¹] and [OH^-1] of a solution with pH = 4.55?
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