how can i calculate the ph of a stock acetic acid solution given the following: pKa of acetic acid=4.75, concentration of acetic acid = 1.1009M.
then, how can i calculate the ph of a stock sodium acetate solution given the following: concentration of sodium acetate = 1.0113M.
Let's call acetic acid (CH3COOH) just HAc and call acetate ion (CH3COO^-) just Ac^-. That makes easier typing. Also, I don't know what you are using a molarity of 1.1009. That is far more accuracy than the pKa value. Those certainly are not that accurate. Anyway,
...............HAc ==> H^+ + Ac^-
I...............0.100......0.........0
C..............-x............x.........x
E.............0.100-x.....x.........x
Convert pKa to Ka with pKa = -log Ka, then
Substitute the E line above into the Ka expression of
Ka = (H^+)(Ac^-)/(HAc) and solve for x = (H^+), then convert that to pH.
For the acetate, the pH is determined by the hydrolysis of the acetate ion.
...............Ac^- + HOH ==> HAc + OH^-
I..............1.01......................0...........0
C..............-x.........................x...........x
E.............1.01-x....................x..........x
Kb for Ac^- = (Kw/Ka for HAc) = (HAc)(OH^-)/(HAc)
Plug the E line into the Kb expression and solve for x = (OH^-) and convert that to pH.
Post your work if you get stuck.
im still not sure how to get Kb.
so for ka i did 10^-4.75 and got 1.78x10^-5. then using the ice table and the 1.1009 for HA, i got x=4.4x10^-3. then to get the ph, i did -log(x) = 2.35.
do i use the same ka of 1.78x10^-5 for kb?
To find Kb the formula is Kb=Kw/Ka, and Kw=1x10^-14. Just replace the values, using the Ka you found.
got it, thank you!
To calculate the pH of a solution, you need to consider the dissociation of the acid or base in water and the concentrations of the species involved. In both cases, you are dealing with acetic acid, which is a weak acid.
1. Calculating the pH of an acetic acid solution:
The dissociation of acetic acid (CH3COOH) in water can be represented by the equation: CH3COOH <--> H+ + CH3COO-
To calculate the pH of the acetic acid solution, you can use the Henderson-Hasselbalch equation, which relates the pH, pKa, and the concentrations of the acid and its conjugate base.
Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA])
Where:
pH - The pH value we want to determine.
pKa - The ionization constant of the acid.
[A-] - Concentration of the conjugate base (acetate ion, CH3COO-).
[HA] - Concentration of the acid (acetic acid, CH3COOH).
Given that the pKa of acetic acid is 4.75 and the concentration of acetic acid is 1.1009 M:
1. Calculate the concentration of acetate ion ([A-]) based on the equilibrium: [A-] = [H+] = x (assuming complete dissociation).
2. Calculate the concentration of acetic acid ([HA]) as the initial concentration minus the concentration of the dissociated species: [HA] = 1.1009 M - [A-].
3. Substitute these values into the Henderson-Hasselbalch equation and solve for pH.
2. Calculating the pH of a sodium acetate solution:
When sodium acetate (CH3COONa) is dissolved in water, it dissociates into the acetate ion (CH3COO-) and sodium ion (Na+). The acetate ion acts as a weak base.
To calculate the pH of the sodium acetate solution, you need to consider the hydrolysis of the acetate ion:
CH3COO- + H2O <--> CH3COOH + OH-
The pH can be calculated by considering the concentration of hydroxide ions ([OH-]) produced by the acetate ion hydrolysis. The hydroxide concentration can then be used to calculate the pOH, which can be converted to pH.
1. Calculate the concentration of hydroxide ions ([OH-]) produced by considering the concentration of sodium acetate (1.0113 M) as the concentration of acetate ion ([A-]).
2. Use the [OH-] concentration to calculate the pOH.
3. Convert the pOH to pH using the equation: pH = 14 - pOH.
Remember to consider any concentrations in Molarity (M) and perform any necessary conversions before substituting values into the equations.