Calculate the change in pH to 0.01 pH units caused by adding 10. mL of 2.72-M NaOH is added to 490. mL of each of the following solutions. a) water pH before mixing = pH after mixing= pH change = b) 0.138 M NH41+ pH before mixing = pH after mixing= pH change = c) 0.138 M NH3 pH before mixing = pH after mixing= pH change = d) a buffer solution that is 0.138 M in each NH41+ and NH3 pH before mixing = pH after mixing= pH change =