IB. Test with a base )Mix about 1 g of stearic acid (a fatty acid CH3(CH2sCOOH)

Question

IB. Test with a base )Mix about 1 g of stearic acid (a fatty acid CH3(CH2sCOOH) in about 10 ml of H20 in a large test tube. Heat in a water bath for several minutes. Record your observations. Add 1 to 2 drops of phenolphthalein to the test tube. Neutralize the stearic acid by slowly adding 50 % NaOH. During this addition stir the mixture and eep it hot until it becomes homogeneous and remains pink. (You might have to add a few more ml of NaOH if the solution begins to turn white). Remove a portion of the solution. Note the consistency of the sample. Shake the solution vigorously and note any suds formation (Explain). i) To a portion of solution from above (i) slowly add 6M HCl until the solution again becomes acidic (phenolphthalein should change from pink to colourless). Compare the results from this test to those in parts i) and ii). Vigorously shake the solution and again note any suds formation.

Explanation / Answer

part i)CH3(CH2)16COOH(s) +H2O(l)---->CH3(CH2)16COOH(aq) [solvolysis rxn]

part ii) CH3(CH2)16COOH(aq) +NaOH (aq) --->CH3(CH2)16COONa(aq) +H2O(l) [neutralization rxn]

sodium salt of stearic acid:CH3(CH2)16COONa

part iii) CH3(CH2)16COONa (aq) + HCl(aq) ----> CH3(CH2)16COOH (aq) +NaCl(aq) [salt hydrolysis or deneutraization of salt of fatty acid]

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