A weak acid HA (pka=6.00) was titrated with 1.00M NaOh. The acid solution had a volume of 100ml and a concentration of .100M. Find the pH at the following volumes of added base. Vb=20ml
millimols acid = mL x M = 100 x 0.1 = 10
millimols NaOH = 20 x 1 = 20
So all of the acid is neutralized and y ou have 10 mmols NaOH in excess.
So (OH^-) = mmols/total mL = 10/200 = 0.1
pOH must be 1 so pH must be 13.
Note that 10/200 is not 0.1 but is ?
Then pOH = -log(OH^-). Calculate pOH.
Then pH + pOH = pKw = 14.
You know pKw and you know pOH, solve for pH.
pH=5.41 after adding 20ml of 0.100M NaOH into 100ml of 0.100M HA
I would have posted my solution, but the site monitor keeps kicking out my post as a website post.
This is an acid/base titration with a common ion. Hope you can get a solution.
To find the pH at a given volume of added base, we need to determine the amount of acid that has been neutralized and the amount of remaining acid in the solution.
1. Calculate the moles of acid initially present:
Number of moles = concentration (M) x volume (L)
Number of moles of HA = 0.100M x 0.100L = 0.010 moles
2. Calculate the moles of base added:
Number of moles of NaOH = concentration (M) x volume (L)
Number of moles of NaOH = 1.00M x 0.020L = 0.020 moles
3. Calculate the moles of acid neutralized by the base:
This is determined by the stoichiometry of the reaction between the acid and the base. Assuming a 1:1 ratio between the acid and the base, we can determine that 0.020 moles of acid have been neutralized.
4. Calculate the moles of remaining acid:
The initial moles of acid minus the moles of acid that were neutralized by the base will give us the moles of remaining acid.
Moles of remaining acid = Initial moles of HA - Moles of acid neutralized
Moles of remaining acid = 0.010 moles - 0.020 moles = -0.010 moles
5. Calculate the concentration of remaining acid:
The concentration of the remaining acid can be determined by dividing the moles of remaining acid by the total volume of the solution after the addition of the base.
Concentration of remaining acid = Moles of remaining acid / Volume of solution (L)
Concentration of remaining acid = -0.010 moles / (0.100L + 0.020L) = -0.100 M
Note: The negative sign indicates that the concentration of the remaining acid is zero, and thus the acid has been completely neutralized.
6. Calculate the pH of the solution:
Since the concentration of the remaining acid is zero, the solution is no longer acidic, and the pH is equal to the pOH. To find the pOH, we can use the pOH equation: pOH = -log[OH-].
In this case, since the base added was NaOH, it dissociates completely to give 1 mole of OH- for every mole of NaOH. Therefore, the concentration of OH- is equal to the concentration of NaOH.
Concentration of OH- = 1.00M = 1 x 10^-1 M
Using the equation pOH = -log[OH-]:
pOH = -log(1 x 10^-1) = -(-1) = 1
Finally, to find the pH, we can use the equation:
pH + pOH = 14
pH + 1 = 14
pH = 14 - 1
pH = 13
Therefore, the pH at a volume of added base Vb = 20 mL is 13.