How do I find the pH of a buffer solution?

Find the pH of each solution

Henderson-Hasselbach equation for pH of a buffer

pH = pKa + [salt] ÷ [acid]

1. 0.67 M formic acid and 0.17 M sodium formate

http://www.bpc.edu/mathscience/chemistry/table_of_...

I found the value of Ka for formic acid at the website above = 1.8 * 10^-4

pKa = -1 * log Ka = -1 * log (1.8 * 10^-4) = 3.74

pH = 3.74 + [0.17] ÷ [1.067]

59.0 mL of 0.50 M HBr is mixed with 100. mL of 0.10 M LiOH

To determine the pH, you need to determine the number of moles of H3O+1 ions per liter of solution.

HBr + LiOH = LiBr + H2O

According to the balanced equation above, 1 mole of HBr reacts with 1 mole of LiOH to produce 1 mole of LiBr and 1 mole of H2O. Using the volume and molarity of the acid and base, determine the number of moles of HBr or LiOH that did not react.

Moles of HBr = 0.059 L* 0.50 mole/L = 0.0295 moles

Moles of LiOH = 0.100 L* 0.1 mole/L = 0.01 moles

Number of moles of HBr that did not react = 0.0295 – 0.01 = 0.0195

The total volume of the solution = 0.059 + 0.100 = 0.159 Liters

Molarity of HBr = 0.0195 ÷ 0.159 = 0.1226

pH = -1 * log 0.1226

I am lost on #3

in case you have 10 ml of the buffer, then you definitely've 0.002 moles of lactic acid and 0.003 moles of sodium lactate present day. once you upload 10 ml of 0.01 M HCl, you're including 0.0001 moles of H+, which will react with the lactate to offer lactic acid. you will now have 0.0021 moles lactic acid and 0.0029 moles lactate, yet your quantity has now greater effective to twenty mL. nonetheless, considering that they are in an identical answer, you ought to use the variety of moles in the Henderson-Hasselbach equation in the ratio of [base]/[acid] to verify pH. pH = pKa + log [base]/[acid] = 3.eighty 5 + log 0.0029/0.0021 = 3.ninety 9 I pretty suspect that the pH of the buffer you calculated previous to the addition of HCl is misguided, or the concentrations are incorrect. If pKa is 3.eighty 5, your pH can't be below that if the concentration of the backside of the conjugate pair is greater than the acid.