Buffers
If you begin with a solution of Benzoic acid, which two specific reagents could you add to the solution to produce a buffer?
Sodium benzoate and NaOH (or any other strong base salt).
Sketch a titration curve of HCl titrated with NaOH. Label the pH at the equivalence point.
Answers vary. pH at equivalence point is 7.
Write the formula for the sodium salt of the conjugate base of acetic acid.
NaCH3COO
Consider the reaction:
2SO2 (g) + O2 (g) <=> 2SO3
Which way will the reaction shift if the pressure increases?
Which way will it shift if the volume increases?
Right (more products)
Left (more reactants)
Find the pKa of a weak acid if a 0.5 M solution of the acid has a pH of 3.5.
pKa = 6.7
If you begin with 0.25 L of 0.5 M solution of acetic acid, what volume (in mL) of 1 M NaOH would you have to add to produce a buffer with pH = 4.74?
62.5 mL of 1 M NaOH
(find moles of Acetic acid. Add half of that number of moles of NaOH to convert half the Acetic acid to Acetate - because pH = pKa so moles of A- = moles of HA.
Sketch a titration curve of NaOH titrated with HCl. Label the pH at the equivalence point.
Answers may vary pH at equivalence point = 7
Write the formula conjugate base of Sodium bicarbonate
Na2CO3
Consider the reaction:
2SO2 (g) + O2 (g) <=> 2SO3
Kc at 25 C has a value of 1.8E-3
Determine the value of Kp at 25 C.
Kp = 7.4E-5 at 25 C.
Find the pH of a 1.0 M solution of Formic acid
pH = 1.87
Find the pH of a buffer composed of 0.4 M disodium Phosphate (Na2HPO4) and 0.75 M Trisodium phosphate (Na3PO4)
pH = 12.7
Draw a titration curve showing the titration of acetic acid with NaOH. Label the pH at the half equivalence point. Explain how you would find the pH at the equivalence point
pH at half equivalence point = 4.74 (pKa)
You could find the pH at the equivalence point by finding the pH of the solution when all of the acetic acid has been converted to acetate.
Write the net ionic equation showing the addition of NaOH to a solution of sodium bicarbonate. Label the conjugate base.
HCO3- + OH- -> CO32- + H2O
Consider the reaction:
2SO2 (g) + O2 (g) <=> 2SO3
If Kp at 350 K has a value of 0.0010
Find Kc at 350 K
Kc = 0.029
Find the pH of a 0.15 M solution of sodium Lactate.
pH = 8.52
If you begin with a solution of Sodium Benzoate, identify two specific reagents you could add to create a buffer out of this solution.
Add strong acid or add benzoic acid.
Draw a titration curve showing sodium acetate being titrated with HCl. Label the pH at the half equivalence point and approximate the pH at the equivalence point.
Write the net ionic equation showing the addition of HClO4 to an acetic acid/sodium acetate buffer.
H3O+ + CH3COO- -> CH3COOH + H2O
Consider the reaction:
2NO3 (g) <=> 2NO2 (g) + O2 (g)
Write the expression for Kc
Kc = [NO2]2[O2]/[NO3]2
Find the pH of a 0.0800 M solution of ammonia.
pH = 11.1
Find the pH of an acetic acid buffer with a TOTAL molarity of 0.7 M, a volume of 50 mL, and a pH of 4.5 after addition of 10 mL of 0.5 M NaOH
pH = 4.75
(find initial moles of A- and HA, subtract moles of OH added from moles of HA, add to moles of A-, then plug in the new number of moles into Hen/Hass eqn to find final pH.
Draw a titration curve showing Carbonic acid being titrated with NaOH. Label the pH at each half equivalence point.
Answers may vary. pH at 1/2 eq point 1 = 6.37. pH at half equivalence point 2 = 10.33
Write the net ionic equation showing the addition of HCl to a Phosphoric acid/monosodium Phosphate buffer.
H3O+ + H2PO4- -> H3PO4 + H2O
2NO (g) + O2 <=> 2NO2
At equilibrium, [NO] = 0.30, [O2] = 0.25, and [NO2] = 0.80. Calculate the value of Kc
KC = 28
Calculate the pH of a 0.25 L, 0.80 M solution of Sodium acetate after the addition of 0.050 L of 1.0 M HCl.
This forms a buffer solution. Total volume is 300 mL. there are 0.15 moles of acetate and 0.05 moles of acetic acid. Use hendersson hasselbach.
pH = 5.2