IN the polystyrene beaker, mix 20mL of 0.1 M Acetic acid and 25mL of 0.1M Sodium Acetate and immediately measure the pH. Remove the electrode and add 5ml of 0.1 M HCl to this buffer. Stir the solution and measure the pH.
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INFO:
concentration of acetic acid= 0.1M- 20ml
concentration sodium acetate= 0.1M- 25ml
concentration of hydrochloric acid- 0.1M - 5ml
pH measured:
Buffer solution- 4.69
Buffer + 5ml 0.1M HCL- 4.43
pH calculated????????????
Buffer solution- ?????
Buffer + 5ml 0.1M HCL- ?????
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PART A:
1.So i have to calculate pH before the addition of HCL
2. show CALCULATIONS for calculated pH after addition of HCl
I think i use the henderson hasselbalch equation:
pH= pka+log [A-]/[HA]
pH= pka+log [0.1][0.1]
I dunt know if i plugged in the right stuff and how do i calculate pka?????
yes and no.
pH = pKa + log (base/acid)
You are right that base is acetate and acid is acetic acid.
You know pH = -log (H^+)
pKa is done the same way.
pKa = -log Ka. If you use 1.8 x 10^-5 for Ka of acetic acid, pKa = 4.74.
Let's call acetic acid HAc, sodium acetate is NaAc and acetate ion is Ac^-.
(HAc) = 0.1 M x (20 mL/45 mL) = ?? in the original solution.
(Ac^-) = 0.1 M x (25 mL/45 mL) = ?? in the original solution.
When adding HCl, the Ac^- ties it up as HAc (which ionizes only partially and that's why this is a good buffer--it won't let the HCl loose to ionize completely) so HAc increases by the amount of HCl added and the Ac^- decreases by the amount of HCl added. My advice is to work in moles or millimoles instead of concn It makes it simpler.
To calculate the pH before the addition of HCl, you can use the Henderson-Hasselbalch equation. The equation is pH = pKa + log([A-]/[HA]), where pKa is the acid dissociation constant of the acid and [A-] and [HA] are the concentrations of the conjugate base and the acid, respectively.
To calculate pKa, you can use the known dissociation constant (Ka). However, in the given information, the dissociation constant (Ka) or pKa values are not provided. Therefore, we will need to find another approach to calculate the pH.
Since you are given the initial concentrations of acetic acid (0.1 M) and sodium acetate (0.1 M), you can use the initial pH of the buffer solution to estimate the pKa value indirectly.
The initial pH of the buffer solution is given as 4.69. This can be considered as the pH at the halfway point between the acidic and basic form of the buffer, where [A-] = [HA].
Now, to estimate pKa, you can assume that at this halfway point, the ratio [A-]/[HA] is 1:1. Therefore, you can substitute equal concentrations (0.1 M) for [A-] and [HA] in the Henderson-Hasselbalch equation and solve for pKa:
pH = pKa + log(1) -> 4.69 = pKa + 0
Thus, from this calculation, we can estimate that the pKa value is approximately 4.69.
Now, to calculate the pH after the addition of HCl, we need to consider that the HCl is a strong acid that will react with the acetate ion (A-) in the buffer solution to form acetic acid (HA). This reaction will cause a decrease in the concentration of A- and an increase in the concentration of HA. As a result, the ratio [A-]/[HA] will change, affecting the pH of the system.
To calculate the pH after the addition of HCl, you can use the Henderson-Hasselbalch equation once again, but this time with the new concentrations of [A-] and [HA] after the reaction with HCl:
pH = pKa + log([A-]/[HA])
Now, you need to determine the new concentrations of [A-] and [HA]. Given that you added 5 mL of 0.1 M HCl to the buffer solution, you can use stoichiometry to calculate the final concentrations.
Since the volume of the buffer solution is 45 mL (20 mL acetic acid + 25 mL sodium acetate), the final volume after adding HCl will be 50 mL (45 mL buffer + 5 mL HCl).
First, calculate the number of moles of HCl added:
moles of HCl = concentration of HCl * volume of HCl
moles of HCl = 0.1 M * 0.005 L (5 mL = 0.005 L)
moles of HCl = 0.0005 mol
Since HCl and sodium acetate react in a 1:1 ratio, the number of moles of sodium acetate (A-) consumed will also be 0.0005 mol.
Given the initial concentration of sodium acetate (0.1 M) and the volume of the buffer solution (45 mL), you can calculate the final concentration of sodium acetate:
new [A-] = (moles of A- remaining) / (final volume)
new [A-] = (0.1 M * 0.025 L - 0.0005 mol) / 0.05 L
new [A-] = 0.0975 M
Since acetic acid is formed in a 1:1 ratio with the consumed sodium acetate, the concentration of acetic acid (HA) will also be 0.0005 mol/L.
Now, you can substitute the new concentrations ([A-] = 0.0975 M and [HA] = 0.0005 M) and the estimated pKa value (4.69) into the Henderson-Hasselbalch equation to calculate the pH after the addition of HCl.
pH = 4.69 + log(0.0975/0.0005)
Calculating this expression will give you the calculated pH after the addition of HCl.