Find ph. a.) a solution that is 0.170 m in propanoic acid and 0.110 m in potassium propanoate express your answer using two decimal places. b.) a solution that contains 0.690% c5h5n by mass and 0.990% c5h5nhcl by mass express your answer using two decimal places. c.) a solution that is 17.0 g of hf and 27.0 g of naf in 125 ml of solution express your answer using two decimal places

a. pH = 4.69    b. pH = 5.22   c. pH = 2.98

Explanation:

To solve this question we will use the Henderson-Hasselbach equation for buffer solutions:

     pH = pKa + log ( (A⁻)/ (HA) )

where ( HA ) and (( A⁻)) are the molarities of the weak acid and its conjugate base.

Note: In this question we do not need to calculate molarities since

                    M= moles/ V (L)

but the volumes are in the numerator and denominator and calcel each other:)

a. pH = 4.88 + log (( 0.110/0.170)) = 4.69

b. 0.690 %  C₅H₅ 0.990 % C₅H₅Cl

Assume 100 grams solution, then

mol C₅H₅ = 0.690 / 79.1 g/mol = 8.72 x 10⁻³

mol C₅H₅Cl = 0.990 / 115.56 g/mol = 8.57 x 10⁻³

pH = 5.23 + log (( 8.57 x 10⁻³/ 8.72 x 10⁻³ )) = 5.22

c.

mol HF = 17.0 g/ 19.99 g/mol =  0.85

mol NaF = 27.0 g / 41.99 g/mol = 0.64

pH= 3.1 + log (( 0.64/0.85)) = 2.98