Here in this example it says determine the buffering range of a solution containing lactic acid which has Ka=1.4×10-4 and sodium lactate, it's conjugate base. Now here we're looking for a buffering range. Remember that when it comes to your buffer range, the pH range, so the range in which the buffer works most effectively is pH=pKa±1.
Remember that pKa=−log(Ka). So just take the negative log of this Ka value. When we do that, we have 3.85, so that means our buffering range or pH range for the effectiveness of a buffer is equal to 3.85±1.
That would mean our range is 3.85−1 to 3.85+1, which will translate to a range of 2.85 pH to 4.85 pH. OK, this would be our buffering range in which this particular buffer will be most effective.
