[nFlavour]

Hello,

In class, we conducted a lab to find out an unknown organic acid.

Here's what I know about my acid.
- Melting point measured was ~120C
- low solubility (0.066g in 50mL water was difficult to dissolve)
- titrated against 0.65mL of 0.45M NaOH to end point (Phenolphthalein) with 0.066g of my acid.
- white powder or flakes (flat tiny squares). reflects light so some looks sparkly. dissolved in water has a faint foul smell.

I'm not sure if my calculations for the molar mass is right. I calculated the number of moles of NaOH, which is 0.0002925mol. I assumed that this is the number of moles of my organic acid, and with the mass of 0.066g, the molar mass of the organic acid is 225.6 g/mol

When I was researching, I first thought it was citric acid. Citric acid powder looks pretty much the same as my acid powder, melting point is within 30C (pretty decent given errors), molar mass is 192g/mol or 210g/mol. Source: http://en.wikipedia.org/wiki/Citric_acid

However, wikipedia says Citric Acid has a solubility of 73g/100mL which is high soluble unlike mine.

If you have any clue as to what my acid is, please suggests some. I appreciate your time and help. Thanks!

[discodermolide]

Hello,

In class, we conducted a lab to find out an unknown organic acid.

Here's what I know about my acid.
- Melting point measured was ~120C
- low solubility (0.066g in 50mL water was difficult to dissolve)
- titrated against 0.65mL of 0.45M NaOH to end point (Phenolphthalein) with 0.066g of my acid.
- white powder or flakes (flat tiny squares). reflects light so some looks sparkly. dissolved in water has a faint foul smell.

I'm not sure if my calculations for the molar mass is right. I calculated the number of moles of NaOH, which is 0.0002925mol. I assumed that this is the number of moles of my organic acid, and with the mass of 0.066g, the molar mass of the organic acid is 225.6 g/mol

When I was researching, I first thought it was citric acid. Citric acid powder looks pretty much the same as my acid powder, melting point is within 30C (pretty decent given errors), molar mass is 192g/mol or 210g/mol. Source: http://en.wikipedia.org/wiki/Citric_acid

However, wikipedia says Citric Acid has a solubility of 73g/100mL which is high soluble unlike mine.

If you have any clue as to what my acid is, please suggests some. I appreciate your time and help. Thanks!

You need to obtain an accurate melting point, "around 120°C" tells you nothing. "Within 30°C" is not decent, it is useless.

[mpv]

The molar mass indicates that is 225,64 if it is a monocarboxilic 113 if it is a dicarboxilic an so on. Given the fact it has a low solubility it must be a monocarboxylic, and if it forms crystals it must be a fat one. In my oppinion it's c14h26o2, molar mass 226, and probabbly it's myristelaidic for this is the most common one. Hope it help.

[Borek]

The molar mass indicates that is 225,64 if it is a monocarboxilic 113 if it is a dicarboxilic an so on.

No. 450 for dicarboxylic.

if it forms crystals it must be a fat one

Really?

Besides, melting point is completely off. Myristelaidic acid is a liquid at room temp (unless you live in Alaska and love fresh air).

- titrated against 0.65mL of 0.45M NaOH to end point (Phenolphthalein) with 0.066g of my acid.

If you started with 0.066g, your determination of the equivalent mass has only two significant digits. It is not 225.6, but around 220-230.

[mpv]

I still think it's half not double. One mole of dicarboxylic consumes double the amount of base, so for a give mole of base you need half the amount of acid.

[Borek]

I still think it's half not double. One mole of dicarboxylic consumes double the amount of base, so for a give mole of base you need half the amount of acid.

Yes, 1 mole of dicarboxylic acid neutralizes two moles of the base. It means one equivalent mass is half of the mole, so the molar mass is twice the equivalent mass.

[mpv]

Ok, you are wright. Sorry about that.

[nFlavour]

You need to obtain an accurate melting point, "around 120°C" tells you nothing. "Within 30°C" is not decent, it is useless.

Hi. The temperature that I read off the thermometer was the first moment that I saw the acid melt, which is 120C. However, the temperature reading on the thermometer was changing rapidly, so uncertainty of at least +-2C. I'm sure there are errors associated with our equipments. Surely, it'd be easy to find what the acid is if I had an accurate melting point measurement. But I don't trust our lab equipment, it gives only an idea of the range.

The molar mass indicates that is 225,64 if it is a monocarboxilic 113 if it is a dicarboxilic an so on. Given the fact it has a low solubility it must be a monocarboxylic, and if it forms crystals it must be a fat one. In my oppinion it's c14h26o2, molar mass 226, and probabbly it's myristelaidic for this is the most common one. Hope it help.

Thanks for suggesting it, but it seems that it is not the acid that I am looking for. But, really appreciate your *delete me*

[discodermolide]

You need to obtain an accurate melting point, "around 120°C" tells you nothing. "Within 30°C" is not decent, it is useless.

Hi. The temperature that I read off the thermometer was the first moment that I saw the acid melt, which is 120C. However, the temperature reading on the thermometer was changing rapidly, so uncertainty of at least +-2C. I'm sure there are errors associated with our equipments. Surely, it'd be easy to find what the acid is if I had an accurate melting point measurement. But I don't trust our lab equipment, it gives only an idea of the range.

Then calibrate the thermometer.
If the temperature reading was changing rapidly then you were heating the sample too fast. As you approach the melting point you should be increasing the temperature by around 0.5°C a minute.

[lespaul]

Going to take a wild guess and say butyric acid - its very foul smelling and not very soluble in water.

[nFlavour]

Then calibrate the thermometer.
If the temperature reading was changing rapidly then you were heating the sample too fast. As you approach the melting point you should be increasing the temperature by around 0.5°C a minute.

Thanks for the suggestion. Our equipment was pretty poor. Just a regular alcohol thermometer and an iron block placed on a hot plate. Couldn't expect too much from it. :p I'll be sure to include that in my analysis.

But do you have any idea what the acid could be, if you were to ignore the melting point? Thanks

[fledarmus]

Going to take a wild guess and say butyric acid - its very foul smelling and not very soluble in water.

Butyric acid has a molecular weight of 88 - measured molecular weight is some multiple of ~220

[discodermolide]

Then calibrate the thermometer.
If the temperature reading was changing rapidly then you were heating the sample too fast. As you approach the melting point you should be increasing the temperature by around 0.5°C a minute.

Thanks for the suggestion. Our equipment was pretty poor. Just a regular alcohol thermometer and an iron block placed on a hot plate. Couldn't expect too much from it. :p I'll be sure to include that in my analysis.

But do you have any idea what the acid could be, if you were to ignore the melting point? Thanks

You can't ignore the MPt. it is a part of your data for this unknown compound.
That's why you should do it properly.
You have a suggestion here, obtain a pure sample and compare the MPt's. and do a mixed MPt. of the known with the unknown.

[mpv]

It could also be a phenol, for example Butylated hydroxytoluene is a white powder and it is in the molar mass range, but the solubility is way smaller. How about adding some FeCl3 to see if it gives some colors.

[nFlavour]

Thanks guys for your help, but I gave my guesses and they were wrong.

Apparently, it was just aspirin, acetylsalicylic acid...

Anyways, thanks everyone for the help.