Chemistry H
May 12, 2016
“Concentrate” on Titration
The purpose of a titration experiment is to find the concentration of an unknown acid or base. To find the concentration you have to neutralize it with a measured quantity of a case or acid solution whose concentration is known. The known solution is the titrant and the unknown solution is the analyte in titrations. In our experiment we put NaOH in a burette and in a beaker we had HCl acid and placed one drop of pH indicator. And we put it on the magnetic stirrer and dripped out the NaOH into the beaker until it became a light pink color. As mentioned before the purpose is to find the concentration of an unknown base or acid.
Procedure:
- Into the burette pour 40 mL of NaOH
- Then put a stir bar in a 500mL beaker
- Into the beaker pour 20 mL of HCl acid
- Next place one drop of phenolphthalein (pH indicator) into the same beaker
- Put the beaker on the magnetic stirrer and turn it on.
- To let the NaOH out, use the stopcock to let it out little by little into the beaker. Let it drip out until the solution becomes a light pink color.
- If the solution turns too dark such as like fuchsia, then add 1 mL of HCl acid to the solution to make it clear.
- Record the initial and final volumes of both solutions.
Analysis:
I compared my results with three other people. I surprisingly didn’t have to change anything. All of our answers were under 1 which was fine. But there still can be many things that effect the data. The largest sources of error in this experiment are:
- The materials used might have not been properly cleansed from any past labs
- Any solutions or substances might have made contact with the current solutions with being used for the lab.
- Not recognizing the pink color instantly
- This would have allowed more NaOH to drip out of the burette
Conclusion:
Equation: [pic 1]
After researching how titration can be used to determine Ka, I’ve found that you have to track the volume of base used as well as pH. Note the pH at equivalence point, the half-equivalence point occurs at the point where you have half the volume of the base used to reach the equivalence point. At the half-equivalence point, this is true: pH=pKa. The experiment can be modified in a way that you have the half volume of the base to reach the point.