Potassium Acid Phthalate for
Sodium Hydroxide (NaOH) will lose strength through age and exposure to carbon
dioxide. By testing its strength against a standard such as Potassium Acid Phthalate (KaPh),
you can either adjust the TA by calculation or pick up new sodium hydroxide. It is always
advisable to test any newly made or purchased solution anyway.
Procedure: Pipet five (5) milliliters (ml or cc) of Potassium Acid
Phthalate .1N into a water glass or flask. Add 5 drops of phenolphthalein to the sample and
50-100 ml of distilled water. Titrate with the .1N (N10) Sodium Hydroxide (NaOH) until
the end point is reached. The end point is the first faint pink blush that persists for at
least 20 seconds while stirring the sample. Record the quantity of NaOH used and calculate as
follows: IF exactly 5 ml of sodium hydroxide was used, then it (the sodium hydroxide) is
still at its full strength. Proceed to use it without any mathematical adjustment.
The Normality of the NaOH is equal to the milliliters of KaPh used times (*) its
normality (.1)divided by the milliliters of NaOH used.
N of NaOH = ml KaPh * (times) 0.1 divided by ml of NaOH used.
N NaOH = ml KaPh *(times)
N NaOH = 5 X(*) .1 = .50
ml of NaOH used say 6 ml was used
.50 .50 divided by 6
To correct the acidity reading obtained using that NaOH:
Acidity reading TA obtained (times)* actual Normality calculated (0.0833) divided by .1 for the
correct TA for the wine or juice that was tested.