How much soap (C18H35NaO2) is produced when 21 grams of NaOH (lye) reacts with goat milk?

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t-nez eNotes educator| Certified Educator

Soap is made by a reaction called saponification, in which fat is heated with sodium hydroxide or potassium hydroxide. A fat molecule consists of a glycerol backbone with three attached long chain fatty acids. During the saponification process the three fatty acids are removed from the glycerol, their acidic hydrogens are removed and each one associates with a sodium or potassium ion to form a soap molecule. In this case sodium hydroxide is being used, and one sodium ion reacts per soap molecule produced. 

The mole ratio of soap (C18H35NaO2) to NaOH is 1:1.

The molar mass of NaOH is 40.0 g/mol

The molar mass of C18H35NaO2 is 308 g/mol

The mass of soap produced is:

(21 grams NaOH)(1 mol/40.0 g)(1 C18H35NaO2/1 NaOH)(308 g/mol) = 161.7 g