Indicators are weak acids and bases, having varying degrees of dissociation. M NaOH 4. Concentrations of hydrogen and hydroxide ions can vary over a very wide range of magnitudes. A much more convenient way of dealing with this wide range of numbers is made possible by using a log scale of concentrations, i.e., the pH scale. Determine the pH and pOH for each of the solutions in problems 1 - 4 above.
Similar options are possible for all other substances appearing in the equilibrium expression.
However, it is often true that a pre-equilibrium reaction will have to be taken into account before the equilibrium expression can be used. This will have to be checked after the value of x is known. Suppose 20.00 ml of 0.15 M HCl is added to 100.00 ml of a 0.10 M NH3 solution. Again try the short-cut that x will be very small compared to 0.0583 and 0.025, and might be neglected.