Question

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

Answer 1

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

Step-by-step 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