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Potassium Acid Phthalate for
Sodium Hydroxide

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) 0.1
                       ml NaOH               

N NaOH = 5 X(*) .1  = .50    
                   ml of NaOH used say 6 ml was used 

.50            .50 divided by 6 = .0833

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.


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