pH curves and titrations

pH curves

show the results of a titration reaction

pH metre

tells you the pH of the solution

how to calibrate a pH metre

Place the bulb of the pH metre into distilled water and allow the reading to settle. Adjust the reading so it shows a pH of 7. Do the same with a standard solution of pH 4 and pH 10. Make sure to rinse the probe with distilled water in between each reading.

strong acid/strong base pH curve

Starts at a pH of 1 as there’s an excess of strong acid and ends around pH 13 as there’s an excess of strong base

strong acid/ weak base

Starts at a pH of around 1 and finshes around a pH of 9 as there’s an excess of weak base

weak acid/strong base pH curve

starts at a pH of around 5 and ends at a pH of around 9 (no neutralisation occurs)

what is the midpoint of the vertical section

at this point [H+] = [OH-]

what if you titre a base with an acid instead

The shapes of the curves are the same but reversed

types of indicators

Phenolphthalein and methyl orange

phenolphthaline colour change

goes from colourless to pink at a high pH

methyl orange colour change

goes from red to orange at a high pH

how to choose a indicator for a titration

choose an indicator that changes colour over the pH’s that occur in the vertical section of the pH curve