Sample Lab Questions Investigation #7: "The Science of Soap"

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1.

(2pts) Describe the procedure for vacuum filtration.

2.

(2pts) Briefly explain how soap works when used to clean oily dirt from an object (or your body). (You may include a picture.)

3.

a. (1 pt) Define hard water.

b. (2 pts) Define hydrophobic and lipophilic. Then give a formula for soap and label the hydrophobic and lipophilic portions of the molecule.

4.

(2pts) A student made soap by the following reaction:
C₅₁H₉₈O₆ + 3NaOH 3NaC₁₆H₃₁O₂ + C₃H₈O₃ If the student reacted 30.6 g of oil with excess NaOH, calculate his theoretical yield of soap.

5.

(5pts) A person takes a bath every day for a week (7 days) in a bathtub containing 110 liters of water that contains 152 mg of calcium hydrogen carbonate [Ca(HCO₃)₂] per liter of water. How many grams of soap will be used during this week to remove all of the calcium ions as calcium stearate from the bath water? (Assume the soap is pure sodium stearate and that calcium stearate is completely insoluble in the bath water. The formula of calcium stearate is [CH₃(CH₂)₁₆CO₂]₂Ca.)

Answers

4. 31.7 g soap
5. 443 g soap