d. Solid Acid Titration
- Page ID
- 309478
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In this lab you are going to design an experiment to determine the Ka for a solid acid. This time you will be required to use dilute (0.1 M) solutions of the titrant, and need to figure how much of the unknown acid you need to dissolve in 50 ml of water for it to be neutralized by 25 ml of the 0.1 M NaOH. Instead of doing an entire titration curve you will just make one pH measurement, although you are welcome to waste your time and do an entire titration curve.
You need to dilute your stock 1.0 M NaOH solution to 0.1M for two reasons.
- In the real lab it is safer.
- Some of the acids have low solubilties, and by using a dilute base you do not need huge amounts of water to dissolve the acid, but all the acid must be dissolved before you start the experiment. 50 ml should be enough water to dissolve the acid.
Note, you can obtain the molecular formula of your acid by toggling the "Aqueous Species Viewer" of the View Menu in the Virtual Lab, and you should also toggle on the "Solid Species Viewer" to be sure all the analyte has dissolved. Because your measured value is the mass of the acid you titrate the volume of water makes no difference.
Your essential procedures are to:
- Make 0.1 M NaOH (titrant) from the stock solution in the Virtual Lab
- Calculate the mass of your acid required to neutralize 25 ml of the 0.1 M NaOH solution
- Dissolve that mass of acid into water (make sure you add enough water so it all dissolves), we suggest 50 ml.
- Calculate the Ka by adding enough base to neutralize half the acid.
Important Notes:
- One acid is labeled at KHP in the lab. That stands for Potassium Hydrogen Phthalate
- One acid has a low solubility and you will 50 ml of water to dissolve the unknown acid before you titrate, which should dissolve all the acids (look at the solid species viewer and make sure it is all dissolved
Assignment
Question 1: Dilution of Stock Solutions
As in the previous assignments, make a solution of 0.1 M NaOH
Question 2: Predict Equivalence Point
Put your unknown in the workbench, click on it and then activate the "solid species viewer" in the "View" menu and identify your unknown's formula. Calcualte its formal weight (FW) and then calculate the mass of your unknown that would require 25 ml of the 0.1 M NaOH to neutralize is. NOTE: KHP stand for potassium hydrogen phthalate (not potassium hydrogen phosphorous).
Then using that mass design an experiment that will allow you to calculate the Ka for the unknown acid. Note, there are multiple values on the web, and you need to have the one that is calculated by the Virtual Lab (do not look it up on Wikipedia as that may be wrong). Feel free to make a titration curve if you can not figure how to do this in one measurement, but you have all the information you need to make it in one measurement, like you did in part C of this activity.
Figure \(\PageIndex{1}\): Copy and Paste Caption here. (Copyright; author via source)
3. Calculate KB from the titration curve (using the value of half equivalence). Remember that the Henderson Hasselbach equation is written in terms of hydroxide for a weak base.
Virtual Lab
This virtual lab should load the "Titration of Weak Base" lab, if it says "Default" you need to refresh the page.
