# Why Does pH Equal pKa Plus Log(Salt/Acid) in Titration?

• semc
In summary, during a lab experiment, the pH value is calculated from the midpoint of the neutralization and the concentration of salt over concentration of acid. The strength of an acid base can also be determined by its pKa value, which can be affected by factors such as electronegativity and the presence of chlorine. The Henderson-Hasselbalch equation and buffers can also be used to calculate pH values.
semc
During my lab experiment, i am required to titrate acetic acid with sodium hydroxide and i am required to calculate the pKa from the titration curve. I want to ask why is pH=pKa + log(salt/acid) (the pH value is the midpoint of the neutralisation and salt/acid is the concentration of salt over concentration of acid.

Secondly i am required to comment on the strength of acid base on their pKa value. Is there any other factor that affect the strength of acid other then the electronegativity on the oxygen ion causing the ion to be stable/unstable? Am i correct to say that the chlorine on chloroacetic acid causes the electron on the oxygen ion to be MORE delocalised?

$$K_{a}=\frac{[salt][H^{+}]}{[acid]}$$
$$[H^{+}]=K_{a}\frac{[acid]}{[salt]}$$
Then simply take log on both sides, and multiply throughout by -1 to get the 'p'

## 1. What is titration?

Titration is a laboratory technique used to determine the concentration of a substance in a solution. It involves adding a known amount of a reagent to a solution of unknown concentration until a reaction is complete.

## 2. How do you calculate the concentration of a solution using titration?

The concentration of a solution can be calculated using the formula: concentration (mol/L) = (volume of titrant (L) x molarity of titrant (mol/L)) / volume of solution (L).

## 3. What is the purpose of an indicator in titration?

An indicator is used in titration to visually signal when the reaction between the analyte and titrant is complete. It changes color when the endpoint is reached, indicating that the reaction has finished.

## 4. What are some common sources of error in titration calculations?

Some common sources of error in titration calculations include inaccurate measurements of volumes and concentrations, human error in recording data, and incomplete reactions.

## 5. How do you ensure accuracy in titration calculations?

To ensure accuracy in titration calculations, it is important to use precise and calibrated equipment, make multiple trials, and calculate an average value. It is also important to follow proper techniques and precautions, and to be aware of potential sources of error.

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