Using Equilibrium Tables to Solve Problems

Many equilibrium problems can be solved using an equilibrium table. The table is constructed with a column under each species in the equilibrium equation, and three rows labeled i (initial), c (change), and e (equilibrium). (This is why such a table is sometimes referred to as an ice table.) 

We use pH to determine the equihbrium concentration of H p+] = lo-pH = 10-3 82 = 15 X IQ- M Because the ionization of HA produces equal amounts of H the equilibrium concentration of A- is also 1.5 X 10 these concentrations in the bottom row of the table. 

To complete the last row of the table, we also need the equilibrium value of [HA]. The amount of weak acid that ionized is equal to the amount of H+ jjroduced by the ionization. Therefore, at equilibrium, 

Because the magnitude of is small, we expect the amount of HA ionized (x) to be small compared to 0.10. Therefore, we can assume that 0.10 - x == 0.10. This simplifies the solution to 

With the bottom row of the table complete, we can use these equilibrium concentrations to calculate the value of 

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