Diapers Q&A
Acid-Base problem.?
The sodium salt of lightly crosslinked poly(acrylic acid) is a water-absorbing polymer used in disposable diapers. Poly(acrylic acid) itself consists of −CH2CH(COOH)− repeat units, linked into chains as shown below. The average molecular mass of such a polymer is about 50,000 g/mol. −CH2CH–CH2CH–CH2CH– │ │ │ COOH COOH COOH Poly(acrylic acid) is insoluble in water, but dissolves on the addition of base once 78% of the acid groups have reacted. What is the minimum volume of 0.20 M NaOH that must be added to an aqueous suspension of 5.00 g poly(acrylic acid) to just dissolve the polymer? I am completely lost by this question, any help would be appreciated.
Public Comments
- The avg MM of polymer is not needed to answer question. The MW of each monomer repeat unit (CH2CH(COOH)−) = 56 g/mol. So in 5.00 grams of polymer, there are (5 g)/(56 g/mol) = 0.0893 moles of monomer units. Each monomer unit has one acidic H, so 78% of the acid groups is (0.78)*(0.0893) = 0.06964 moles need to react to dissolve all of the PAA. So we must add 0.06964 moles of NaOH, or because the NaOH solution is 0.2 M, (0.06964 mol)/(0.20 mol/L) = 0.35 L. The minimum volume that must be added is 0.35 L.
