Determination of acidity liberated on acid hydrolysis

Take 5 g of sample in a boiling flask, dissolve in 50 ml water, heating if necessary, and neutralise with 1.0 M hydrochloric acid or sodium hydroxide to phenolphthalein. 

Add exactly 50 ml 1.0 M aqueous hydrochloric acid, heat on a steam bath under reflux for 30 min, then boil under reflux for a further 3 h. 

Cool and back-titrate to phenolphthalein with 1.0 M sodium hydroxide. 

The difference between the two titrations measures the liberated hydrogen ions. 

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