Which statement is not a valid description of pH?

Question

a. it is always less than 7 in the solution of an acid.

b. the pH of 0.1 M HCl is 1

c. the pH of a 0.1 M solution of a weak acid is always less than 7 but more than 1

d. for strong acids, pH=Ka

help me please =]

Answer 1

Basically, d. is wrong because Ka does not go with strong acids. Ka only applies to weak acids that partly dissociate into hydronium and the conjugate base. Ka doesn't matter because strong acids like HCl do not dissociate to any degree but completely.

Answer 2

d. is incorrect. For strong acids, Ka = infinity. For strong acids, Ka is not an appropriate term.

Answer 3

I am sure that A is not a valid description of pH because pH depends on temperature.  The neutral pH is not always 7. The neutral pH depends on the temperature. Therefore acids don't always have a pH that is less than 7.