th a base i) Mix about 1 g of stearic acid (a fatty acid CH3(CH2)16COOH) in abou

Question

th a base i) Mix about 1 g of stearic acid (a fatty acid CH3(CH2)16COOH) 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 keep 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). ii) To a portion of solution from above (i) slowly add 6M HCI 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 i). Vigorously shake the solution and again note any suds formation. i:

Explanation / Answer

1. Stearic acid dissolution,

CH3(CH2)16COOH (s) + H2O ---> CH3(CH2)16COOH (aq) + H2O

2. Neutralization of stearic acid

CH3(CH2)16COOH (aq) + NaOH (aq) ---> CH3(CH2)16COONa (aq) + H2O (l)

Phenolphthalein changes color from initial colorless in acidic medium to final pink in basic medium.

3. After reacidification with HCl, stearic acid is regenerated

CH3(CH2)16COONa (aq) + HCl (aq) ---> CH3(CH2)16COOH (aq) + NaCl (l)

Phenolphthalein changes color from initial pink in basic medium to final colorless in acidic medium.

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