Calculate the ph when 1.03 g of ch3coona (fw = 82.03 g/mol) is added to 36 ml of 0.500 m acetic acid, ch3cooh. ignore any changes in volume. the ka value for ch3cooh is 1.8 x 10-5.

Moles of CH3COONa = mass / molar mass
when mass = 1.03 g and molar mass = 82.03 g/mol 
So by substitution:
                      = 1.03 / 82.03 = 0.0126 moles 

molarity of CH3COONa = moles / volume
                                         = 0.0126 / 0.036 L 
                                         = 0.35 M
then we have to get Pka:
Pka = -㏒Ka
       = -㏒1.8x10^-5
       = 4.74
by using Henderson-Hasselbalch formula:

PH = Pka + ㏒[salt]/[acid]
PH = 4.74 + ㏒ 0.35 / 0.5
      = 4.59

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