Virtual Post Lab 8B - Titration of a Solid Acid

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Titration of a Solid Acid

In this virtual lab you will be given an unknown monoprotic acid and asked to determine it's K_A and molar mass. You are titrating it with sodium hydroxide, a monoprotic base, and so at the equivalent point, the moles acid equal the moles base. Since you know the mass, you can determine the molar mass. Now the challenge is that since you have no idea what the acid is, you have no idea how much of the base stock solution will be needed to neutralize it.

The first thing you need to do is determine how much acid you want to work with, and that not only depends on its molar mass, but the concentration of the base you are using to neutralize it. So you must explore, that is, consider a given quantity of base, say 25 mL of 0.100M NaOH. If two students have different acids with different molar masses, the one who has the larger molar mass will need more of the acid to neutralize the base.

I suggest you look at this from the other side, and instead of asking, how much base do I need to neutralize a given quantity of acid, ask, how much acid do I need to neutralize a given quantity of base. That is, start of with 25 mL of base, and find out how much acid this will neutralize. Once you know that, use that quantity of solid acid in your titration (first diluting with water), and proceed to titrate with a base.

Note: many solid acids are organic compounds and have limited solubilities in water. You need to use a quantity that is small enough to completely dissolve in the amount of water you add (and yet leave enough room in the flask to add the base once you start the experiment). Now, if you use the virtual lab in "precise mode", you can add any quantity of base, that is, 0.00001 mL of 1M. So, you are not confined by the precision of your instruments in the design of your experiment.

Tip: You can answer these questions with just two measurements. You do not need to make a complete titration curve, you only need two points off the curve.

WARNING: Some browsers may cache the default virtual lab, your stock room should have 28 unknowns, and in the upper right corner say Titration of Solid Acid. If it says "Default Lab Setup", go to your browser History and in "Clear browsing data" choose "Cached images and files", and then reload the page.

Note: a downloadable PDF of your assignment is located under the virtual lab.

Downloadable Worksheet