PH and mL through pKa+log[A-]/[HA]

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In summary, the problem involves creating a solution with a pH of 4.19 by adding a certain amount of a 0.246 M HNO3 solution to 213 mL of a 0.00666 M 2,2' -bipyridine solution. The pKa of 2,2' -bipyridine is 4.34 and the Henderson-Hasselbalch equation is used to calculate the concentration of the added HNO3. However, the calculated concentration may not be the correct answer due to possible errors in how the concentrations were calculated.
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1. You have a .246 M HNO3 solution. You also have 213mL of a 0.00666M 2,2' -bipyridine. You want a solution with pH 4.19. How man L of .246M HNO3 do you add to the 213mL other stuff?


2. pH=pKa+log[A-]/[HA] also, pKa of 2,2' -bipyridine is 4.34 I think.



3. pH=pKa+ log[A-]/[HA]
4.19=4.34+log[x-]/[0.00666M-x]
-0.15=log[x-]/[0.00666M-x]
10^-.15=[x-]/[0.00666M-x]
x=5.96x10^-5mol

(5.96x10^-5mol) / (0.246M)= .0002423L or .2423 mL


I know that is not the right answer, I'm just not sure what I am doing wrong. Is this the wrong equation for the problem or is there something else I need to do?
 
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First things first - what is your HA and what is your A-?

Note you have not used volume of the pyridine solution. You are right about using Henderson-Hasselbalch equation, but you need to pay attention to the way you calculate concentrations.
 

Related to PH and mL through pKa+log[A-]/[HA]

1. What is the relationship between pH and pKa?

The pKa is the negative logarithm of the acid dissociation constant (Ka) of a weak acid. It is a measure of the strength of an acid. pH, on the other hand, is a measure of the hydrogen ion concentration in a solution. The relationship between pH and pKa is given by the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the conjugate base and [HA] is the concentration of the acid.

2. How does the concentration of the conjugate base affect pH?

The concentration of the conjugate base ([A-]) in a solution can affect the pH through the Henderson-Hasselbalch equation. As the concentration of [A-] increases, the pH will increase (become more basic) since the log term in the equation will decrease. Similarly, a decrease in [A-] will lead to a decrease in pH (become more acidic).

3. What is the significance of the pKa value?

The pKa value is significant because it is a measure of the strength of an acid. A lower pKa value indicates a stronger acid, while a higher pKa value indicates a weaker acid. The pKa value can also be used to predict the behavior of an acid in a solution, such as how much of it will dissociate into its conjugate base and hydrogen ions.

4. How does the Henderson-Hasselbalch equation relate to the titration of a weak acid?

The Henderson-Hasselbalch equation is used to calculate the pH of a solution containing a weak acid and its conjugate base. During the titration of a weak acid, the concentration of the acid decreases as it is neutralized by a base. The concentration of the conjugate base increases, which affects the pH according to the Henderson-Hasselbalch equation. The equation can be used to determine the equivalence point of the titration, where the pH is equal to the pKa of the acid.

5. What is the role of mL in the Henderson-Hasselbalch equation?

The mL in the Henderson-Hasselbalch equation represents the volume of the solution being analyzed. This volume is important because it is used to calculate the concentration of the acid and the conjugate base, which are needed to determine the pH. Additionally, during a titration, the volume of the solution will change as the acid is neutralized by a base, and this will affect the concentrations of the acid and conjugate base, leading to a change in pH.

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