The cleaning solution for soft contact lenses may contain enzymes, salt, and a b

Question

The cleaning solution for soft contact lenses may contain enzymes, salt, and a buffer.

(a) Suppose a buffer for such a solution was made using boric acid (Ka = 7.2 x 10-10). What would be the pH of a buffered solution that was made from 0.010 M boric acid (HBo) and 0.050 M sodium borate (Bo-) conjugate?

(b) Suppose some material on a pair of soaking lenses brings in some basic compound that, when dissolved, produces 0.0050M OH within the solution. When the buffer comes to equilibrium, what is the new, pH of the buffer?

Explanation / Answer

a) pH =pka + log [Bo-]/[HBo] , pka = -log ( 7.2x10^ -10) = 9.143,

pH = 9.143 + log( 0.05/0.01)   = 9.842

b) HBo + OH- <---> Bo- + H2O

hence [HBo] =( 0.01-0.005) = 0.005, [Bo-] =( 0.05+0.005) = 0.055,

pH = 9.143 + log ( 0.055/0.005) = 10.184

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