Question

1. A dispersion consisting of 1% w/w polyacrylic acid in water is neutralized with a stoichiometric amount (based on carboxylate content) of triethanolamine, creating a gel. What is the approximate ionic strength in the gel? Hint: The repeating unit of PAA (FW 76 Da) is shown below. ??

2 × 10^14 M

0.01 M

0.04 M

0.09 M

0.13 M

2. The same polyacrylate gel composition as given in Question #1 is prepared in ethanol:water (50:50 v:v) rather than pure water. Is the hydroalcoholic gel likely to be more or less susceptible to destabilization by added electrolytes? Note: You may take the dielectric constants, ?r, of ethanol and water to be 24.5 and 80.4, respectively.

More susceptible

Less susceptible

No change is anticipated.

Answer 1

Question 1. 0.13 M

Explanation: (0.1/76) * 100 = 0.13 M

Question 2. Less susceptible

Explanation: By decreasing the polarity of the solvent, i.e. by adding ethanol to water, the dielectric constant decreases. As a result, the hydroalcoholic gel likely to be less susceptible to destabilization by added electrolytes.