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Acid Base Questions PART 1: For 500.0 mL of a buffer solution that is 0.150 M...

Acid Base Questions

PART 1: For 500.0 mL of a buffer solution that is 0.150 M in CH3CH2NH2 and 0.135 M in CH3CH2NH3Cl, calculate the initial pH and the final pH after adding 0.020 molof HCl.

PART 2: A buffer contains significant amounts of acetic acid and sodium acetate. Write an equation showing how this buffer neutralizes added base (KOH).

Expert Solution

Hi, you need the pKa value of ethylamine to do this. If you assume that following equation:

you take the pKa of the protonated form which is 10.7. You might want to put your own value if it differs from your book/table. For the record, I will write the protonated form as HA and the deprotonated form as A-. Although it is not charged but let's stick to the original equation.

, so the pH is

If you add 0.020 mol of HCl, the reaction will be

so, you can subtract the molarity of HCl from ethyl amine and add it to the protonated form and again apply the Henderson-Hasselbalch equation. The molarity of HCl is

so the new concentrations are

ethyl amine = 0.14996 M

ethyl amine protonated form = 0.13504 M

This is logical since you have added a very minute amount of HCl to the solution, so the pH has changed very little.

Now for the second part.

KOH reacts with acetic acid

the amount of acetate increases but the equilibrium is reestablished as

queen_honey_blossom answered 2 years ago

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