For 520.0mL of a buffer solution that is 0.140M in HC2H3O2 and 0.125M in NaC2H3O2, calculate the initial pH and the final pH after adding 0.020mol of HCl
millimols HAc = mL x M = ? = acid
mmols NaAc = mL x M = ? = base.
Plug these into the Henderson-Hasselbalch equation and solve for pH.
part 2. mmols HCl added = 20
I will make up some numbers for mmols HAc and NaAc to make this easier to do but these aren't real numbers. You must go through the calculations above and use those numbers.
...........Ac^- + H^+ ==> HAc
I...........65....0.......75
add..............20...........
C..........-20..-20.......+20
E...........45....0........95
Plug these new E line numbers (after you have the REAL numbers that go there) into the HH equation and solve for the new pH.
How many grams of iron(III) sulfide form when 62.0 mL of
0.135 M iron(III) chloride reacts with 45.0 mL of 0.285 M calcium
sulfide?
To calculate the initial pH of the buffer solution, we can use the Henderson-Hasselbalch equation which is derived from the acid dissociation constant (Ka) of the weak acid in the buffer solution.
The Henderson-Hasselbalch equation is given as:
pH = pKa + log([A-]/[HA])
where pH is the solution's pH,
pKa is the negative logarithm of the acid dissociation constant,
[A-] is the concentration of the conjugate base,
[HA] is the concentration of the weak acid.
First, we need to find the pKa value for HC2H3O2. The Ka value for HC2H3O2 is 1.8 × 10^-5. Therefore, the pKa is calculated as:
pKa = -log(Ka) = -log(1.8 × 10^-5) ≈ 4.74
To calculate the initial pH, we need to determine the concentration of the weak acid ([HA]) and the concentration of the conjugate base ([A-]).
In this case, the concentration of HC2H3O2 ([HA]) is 0.140M, and the concentration of NaC2H3O2 ([A-]) is 0.125M. Both are given.
Now we can substitute the values into the Henderson-Hasselbalch equation:
pH = 4.74 + log(0.125/0.140) ≈ 4.74 - 0.04 ≈ 4.70
Therefore, the initial pH of the buffer solution is approximately 4.70.
Next, let's calculate the final pH after adding 0.020 mol of HCl to the buffer solution.
When HCl is added, it will react with the conjugate base (C2H3O2-) of the buffer solution to form the weak acid (HC2H3O2). This reaction will consume some of the C2H3O2- and shift the equilibrium.
To calculate the final pH, we need to consider how much of the weak acid and the conjugate base remain after the reaction.
The initial moles of HC2H3O2 (weak acid) in the buffer solution can be calculated using the initial volume and the concentration of HC2H3O2:
moles of HC2H3O2 = volume × concentration = 520.0 mL × 0.140M = 72.8 mmol = 0.0728 mol
Now, let's calculate the moles of C2H3O2- (conjugate base) in the buffer solution:
moles of C2H3O2- = volume × concentration = 520.0 mL × 0.125M = 65.0 mmol = 0.0650 mol
Since HCl is a strong acid, it will completely dissociate into H+ and Cl- ions. Therefore, the moles of H+ added can be directly considered as 0.020 mol.
Now, we need to determine which component of the buffer will be consumed and which component of the buffer will be produced.
Since HCl reacts with the C2H3O2- (conjugate base), it will consume a certain amount of the buffer's C2H3O2- and produce an equal amount of HC2H3O2.
The moles of C2H3O2- remaining after the reaction can be calculated as:
moles of C2H3O2- remaining = initial moles of C2H3O2- - moles of H+ added
= 0.0650 mol - 0.020 mol = 0.0450 mol
The moles of HC2H3O2 produced can be calculated as:
moles of HC2H3O2 produced = moles of H+ added
= 0.020 mol
Now, we can calculate the final concentration of HC2H3O2:
final concentration of HC2H3O2 = moles of HC2H3O2 produced / final volume
= 0.020 mol / (520.0 mL + 0.020 mol) = 0.0385 M
The final concentration of C2H3O2- can be calculated as:
final concentration of C2H3O2- = moles of C2H3O2- remaining / final volume
= 0.0450 mol / (520.0 mL + 0.020 mol) = 0.0865 M
Now, we can calculate the final pH using the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
pH = 4.74 + log(0.0865/0.0385) ≈ 4.74 + 0.44 ≈ 5.18
Therefore, the final pH of the buffer solution after adding 0.020 mol of HCl is approximately 5.18.
To calculate the initial pH and final pH of the buffer solution after adding HCl, we need to consider the equilibrium reactions involving the acid (HC2H3O2) and its conjugate base (C2H3O2-) of the buffer system.
Step 1: Write the equilibrium reactions for the acid and its conjugate base:
HC2H3O2 ⇌ H+ + C2H3O2-
In this case, HC2H3O2 donates a proton (H+) to form the conjugate base C2H3O2-.
Step 2: Calculate the initial concentrations of the acid and conjugate base.
Given:
Volume of the solution (V) = 520.0 mL = 520.0 cm³
Molar concentration of HC2H3O2 (Cacetic acid) = 0.140 M
Molar concentration of NaC2H3O2 (Cacetate ion) = 0.125 M
Using the formula:
moles = concentration (M) × volume (L)
Moles of HC2H3O2 = 0.140 M × 0.520 L = 0.0728 moles
Moles of NaC2H3O2 = 0.125 M × 0.520 L = 0.065 moles
Step 3: Calculate the moles of H+ and C2H3O2- in the buffer solution.
Since the buffer solution contains equal moles of HC2H3O2 and NaC2H3O2, the moles of H+ and C2H3O2- are equal to the moles of HC2H3O2 (0.0728 moles).
Step 4: Calculate the initial pH of the buffer solution.
To find the pH, we need to convert the moles of H+ to molarity using the formula:
[H+] = (moles of H+) / volume (L)
[H+] = 0.0728 moles / 0.520 L = 0.140 M
Using the formula for pH:
pH = -log[H+]
pH = -log(0.140)
pH ≈ 0.853
Therefore, the initial pH of the buffer solution is approximately 0.853.
Step 5: Calculate the final pH after adding HCl.
Given:
Moles of HCl added = 0.020 moles
Step 6: Determine the new concentration of the acid and calculate the moles of H+ and C2H3O2- after adding HCl.
Since HCl is a strong acid, it fully dissociates in water to give H+ ions:
HCl → H+ + Cl-
As a result, the moles of H+ in the solution will change.
Using the formula for moles:
Moles of H+ = moles of HCl
Moles of H+ = 0.020 moles
Therefore, the moles of H+ in the solution will increase by 0.020 moles.
Step 7: Determine the new volume of the solution.
To calculate the final pH, we need to know the total volume of the solution after adding HCl. This volume should be the initial volume plus the volume of HCl added.
Total volume of solution = Initial volume + Volume of HCl added
Given:
Volume of HCl added = unknown
You will need to provide the volume of HCl added in order to calculate the total volume and proceed with the final pH calculation.