You are drilling the Marcellus shale and need to provide water with a pH = 4. Yo

Question

You are drilling the Marcellus shale and need to provide water with a pH = 4. You have two acids you can use. One is a concentration solution (3 moles/L) of HCl (a strong acid). The other is a 3 mole/L solution of acetic acid with a pKa = 4.75.

a. Calculate how many mLs of a 3 mole HCl/L solution you need to add to 10 liters of water to drop the pH from 7 to 4. (0.333 mL)

b. Calculate how many mLs of a 3 mole/L acetic acid solution you need to add to 10 gallons to water to drop the pH from 7 to 4. The pKa of acetic acid is 4.75. (2.21 mL)

Explanation / Answer

a.

At pH=4,     [H+] = 1x10-4 M

The quantity of H+, in 10 L water, at pH=4 will be:

1x10-4 mol/L x 10 L =1x10-3 mol

obtained from a volume V

V = 1x10-3 mol / 3 mol/L = 0.000333 L = 0.333 mL of 3M HCL

b.

For the dissociation of the acetic acid:   [H+] = [CH3COO-]

At pH=4,     [H+] = 1x10-4 M

Ka = [H+]2/(cacid

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