CHEMISTRY PLS HELP

Question

If 8.1 g of butanoic acid, C4H8O2, is dissolved in enough water to make 1.0 L of solution, what is the resulting pH? Look up the 𝐾a value in the Table of Ionization Constants.

pH=

Answer 1

Hi Olivia!

You begin with using the molar mass to find the number of moles:

8.1 grams of butanoic acid with molar mass of 88.11 g/mol = 0.09 moles

0.09 moles / 1.0 litre = 0.09 Molar butanoic acic "HA"

HA --> H+ & A-

K_a = [H+] [A-] / [HA]

The K_a value for butanoic acid is 1.52 x 10^-5

1.52 x 10^-5 = [x] [x] / [0.09 - x]

Now assume that 0.09 - x = 0.09 since the value K_a is very small

Therefore,

1.52 x 10^-5 = x² / 0.09

x² = 1.37 x 10^-6

x = 0.0011

Hence, [H₃O⁺] = 0.0011 M

Calculating pH of the solution:

pH = - log [H₃O⁺]

pH = - log (0.0011)

pH = 2.96