I just did a lab on Acids and Bases and I am having trouble with the lab questions I was given to complete.

Question

Concentration of NaOH: 0.09999 M
Volume of NaOH: 3.25 mL
# moles of NaOH: 0.325 moles
Initial Concentration of Weak Acid: ? (How do we calculate this)

Part 2: Hydrolysis of Salts
a) Potassium Chloride has a pH of 7 and a yellow-green universal colour indicator. Explain with an equation to show hydrolysis
b) Sodium Acetate has a pH of 8 and a dark green universal colour indicator. Explain using equation
c) Ammonium Chloride has a pH of 5.5 and orange universal colour indicator. Explain using equations.

Part III: Buffers
Concentration of acetic acid (0.1 M volume used) : 20 mL
Concentration of sodium acetate (0.1 M volume used) : 25 mL
Concentration of hydrochloric acid (0.1 M volume used) : 5 mL

pH Measured of buffer solution: 4.55
pH Measured of buffer +5 mL of 01 M HCl: 4.20
We have to now determine the pH calculated for both solutions above.

I would greatly appreciate the help or any guidance to these questions. Thanks!

DrBob222 · Answer

Concentration of NaOH: 0.09999 M
Volume of NaOH: 3.25 mL
# moles of NaOH: 0.325 moles
Initial Concentration of Weak Acid: ? (How do we calculate this)

There isn't enough information to work the problem here. (weak acid) = moles NaOH/volume weak acid used in the titration. All this is ok if the acid is a monoprotic acid.

Part 2: Hydrolysis of Salts
a) Potassium Chloride has a pH of 7 and a yellow-green universal colour indicator. Explain with an equation to show hydrolysis
b) Sodium Acetate has a pH of 8 and a dark green universal colour indicator. Explain using equation
c) Ammonium Chloride has a pH of 5.5 and orange universal colour indicator. Explain using equations.
KCl doesn't hydrolyze; therefore, the pH is 7.0.
Part b. Sodium acetate. Sodium is not hydrolyzed but acetate is producing acetic acid and hydroxide ion. You can write the equation and see that the solution is basic.
part c. NH4Cl. Cl is not hydrolyzed. NH4^+ is. I will let you write the equation to obtain H3O + ?? showing that the solution is acidic.

Part III: Buffers
Concentration of acetic acid (0.1 M volume used) : 20 mL
Concentration of sodium acetate (0.1 M volume used) : 25 mL
Concentration of hydrochloric acid (0.1 M volume used) : 5 mL

pH Measured of buffer solution: 4.55
pH Measured of buffer +5 mL of 01 M HCl: 4.20
We have to now determine the pH calculated for both solutions above.

Use the Henderson-Hasselbalch equation.

Lalu · Answer

Thanks for the help