Please provide explanation of steps so I can get better at doing these on my own

Question

Please provide explanation of steps so I can get better at doing these on my own, thank you!!!

1) A buffer solution is prepared by adding 2.45 g of benzoic acid (C6HsCOOH, MW = 122.1 g/mol, Ka- 6.5 x 105) and 1.18 g of sodium benzoate (C6H5COONa, MW 1441 g/mol) to water, to form a solution with total volume V = 500.0 mL. a) What is the pH of the above buffer solution? b) 0.010 g of sodium hydroxide (NaOH, MW = 40.0 g/mol) is added to the above solution. What is the pH after the addition of the sodium hydroxide? You may assume that the volume remains constant.

Explanation / Answer

pka of C6H5COOH = -logKa

               = -log(6.5*10^-5)

               = 4.19

no of mol of benzoicacid = 2.45/122.1 = 0.02 mol

no of mol of sodium benzoate= 1.18/144.1 = 0.0082 mol

pH = pka + log(salt/acid)

     = 4.19+log(0.0082/0.02)

     = 3.8

b) no of mol of NaOH added = 0.01/40 = 0.00025 mol

pH = pka + log(salt+NaOH/acid-NaOH)

     = 4.19+log((0.0082+0.00025)/(0.02-0.00025))

     = 3.82

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