Question

I'm supposed to write a procedure to determine the identity of a solid organic compound and I've decided to use a standardized NaOH solution to help determine the molar mass of the acid after I perform a couple of titrations. I just read over my procedure and saw that I had included a KHp portion. I can't remember why I did it. Is it even necessary for what I'm doing?

Answer 1

Your first titration will be to standardize your NaOH solution right? Could it be that you are using a KHp solution as your primary standard?

Answer 2

Yes, I will be standardizing my NaOH solution first.
Would it be necessary to do the KHp as the primary?
Or would it just be smart to do it as a "just in case?"

Answer 3

Well if you want to be accurate it is best to standardize your NaOH solution before doing any titrations with it. KHp is apparently very good as a primary standard as it is air stable and easy to weigh

Answer 4

Just prepare a KHp solution very carefully then make your NaOH solution then do a titration to figure out the true molarity of the NaOH solution. NaOH is a messy chemical to weigh :S so yeah it is important to standardize it

Answer 5

I hope that this is helpful not knowing your procedure I do not know where you are including your portion of KHp. Perhaps one of your indicators requires a buffer?

Answer 6

It is and thank you! Here's the procedure I have so far. I haven't refined it and I'm still doing some research.
1. Obtain 1.5 ml of ~19M NaOH into a flask and add distilled water to the flask until a volume of roughly 150mL is reached.
2. Measure the pH of the solution.
3. Perform the calculation M1V1=M2V2
4. Clean out a burette and inspect for any possible flaws. Proceed to fill the burette with NaOH solution and be sure to release any air bubbles.
5. Obtain the solid organic acid and dissolve in distilled water.
6. Weigh a clean, dry flask.
7. Add 3 mL of your liquid organic acid to the flask and weigh. Measure the pH and add ~25 mL of distilled water in addition to a few drops of phenolphthalein indicator.
8. Record the initial volume of NaOH and begin to slowly add the NaOH to your swirling acid unknown acid solution until a faint pink color, sustainable for roughly 30 seconds appears.
9. Record the final volume of NaOH so you know how much was needed to neutralize the solution.
10. Repeat from step 6.
11. Obtain roughly 0.4-0.5g of KHp and record the weight.
12. Add about 25mL of distilled water and proceed to titrate.
13. Once the titration is complete, record the pH and repeat one last time from step 11.
14. Perform the following calculations

Answer 7

Sorry, the calculations got cut off.
Number moles (NaOH)=M×V
M (NaOH)=(mol NaOH)/(titration volume (L))
Molar Mass=(Mass Unknown)/(Molar Mass)

I didn't plan on using the KHp anywhere yet I have it in my procedure.

Answer 8

Oh I think it is to standardize

Answer 9

You are standardizing after

Answer 10

which is weird but it would still work

Answer 11

Determining your unknowns Molar Mass:
1. Obtain 1.5 ml of ~19M NaOH into a flask and add distilled water to the flask until a volume of roughly 150mL is reached.
2. Measure the pH of the solution.
3. Perform the calculation M1V1=M2V2
4. Clean out a burette and inspect for any possible flaws. Proceed to fill the burette with NaOH solution and be sure to release any air bubbles.
5. Obtain the solid organic acid and dissolve in distilled water.
6. Weigh a clean, dry flask.
7. Add 3 mL of your liquid organic acid to the flask and weigh. Measure the pH and add ~25 mL of distilled water in addition to a few drops of phenolphthalein indicator.
8. Record the initial volume of NaOH and begin to slowly add the NaOH to your swirling acid unknown acid solution until a faint pink color, sustainable for roughly 30 seconds appears.
9. Record the final volume of NaOH so you know how much was needed to neutralize the solution.
10. Repeat from step 6.

NaOH Standardization Method:

11. Obtain roughly 0.4-0.5g of KHp and record the weight.
12. Add about 25mL of distilled water and proceed to titrate.
13. Once the titration is complete, record the pH and repeat one last time from step 11. 14. Perform the following calculations

Answer 12

you are doing it in 1 titration set up instead of two titration set ups which makes sense it saves time

Answer 13

I can tell you right now you wont be able to make an accurate weigh of NaOH also I'm pretty sure it is reactive with air, so standardizing your solution is a must for accurate trust worthy results

Answer 14

Thank you so much! I makes more sense now that I realize what the KHp was for. I knew I had it in there for a specific reason but I got lost after reading it over and over again.
Sadly supplies are limited so I only get to work with a bit of the equipment that the campus provides. I get to work with whatever is in my drawer and the rest I have to share :/

Answer 15

Oh fair enough is this the only method you are following to identify the acid? Just out of curiosity?

Answer 16

Yes. It's the only one I could think of and was suggested by the professor.

Answer 17

If only you had access to an nmr instrument, or combustion chamber would be a lot easier. I might have a ppt on identifying unknown carbon molecules if you are interested?

Answer 18

This note provides a number of classical methods to identify organic compounds it may be of help to you, also if you can find a merc index that might also be helpful :)

Answer 19

*Merck Index

Answer 20

I can only dream of using equipment like that at the moment! I'm just starting out and haven't even been exposed to it yet. I'll definitely have to wake up early tomorrow and check it out. I love looking into things I haven't been exposed to yet because I know sometimes in the future it'll come up or aide me in some way.
Are you a professor? I ask out of curiosity. You're so smart!

Answer 21

lol, no I'm a lowly undergrad student right now and a laboratory technologist.