BIOL 1406

PreLab 3.7

How do I plot a titration curve?

Titration is a procedure for inferring certain properties of a solution by carefully measuring how much of a second solution must be added in order to produce a specific change (such as a change in color or pH).  For example, in acid-base chemistry we can gradually add acid or base to a solution while measuring its pH in order to determine the buffering range and buffering capacity of the solution. The buffering range of a solution refers to the range of pH values where the solution acts as a buffer (resists changes in pH.) The buffering capacity of a solution refers to the amount of acid or base that can be added to the solution without going beyond the buffering range.


Use the interactive exercise below to learn more about titration.


To plot an acid-base titration curve, first draw the 2 axes of your graph. You should place the volume of acid or base added to the unknown solution (your independent variable) on the x-axis, and place the pH of the unknown solution (your dependent variable) on the y-axis. Plotting of the x-axis is slightly different compared to previous graphs we have made. In this case, the zero point should be placed in the MIDDLE of the x axis, and the volume of base added should increase as you move to the right of the zero point while the volume of acid added should increase as you move to the left of the zero point. A simple way to do this with a graphing program such as Excel is to use positive values to represent the volume of base added (e.g. let 10, 20, and 30 represent 10, 20, and 30 mLs of base added) and use negative numbers to represent the volume of acid added (e.g. let -10, -20, and -30 represent 10, 20, and 30 mLs of acid added.) If you use this approach, make sure it is clearly indicated on your graph.

After you have labeled the axes of your graph, plot the data points and draw a smooth curve as close as possible to all of the points. The resulting plot is referred to as a titration curve. The titration curve serves to profile the unknown solution. The shape of the curve reveals much chemistry including information about the buffering range and buffering capacity of your unknown solution.


The following graphs show the titration curves of two unknown solutions:
What is the buffering range of solution A? Hint Check your answer.
What are the buffering ranges of solution B? Hint Check your answer.
Which solution has the greater buffering capacity? Hint Check your answer.
Would either solution be a good buffer for studying enzymes or other biomolecules found in human blood? Explain your answer. Hint Check your answer.


Close this browser window to return to Blackboard and complete the practice quiz and assessment quiz.