[pcm81]

I just got some 99.6% pure oxalic acid dihydrate to use for KMnO titration, to standardize the KMnO for further iron content titrations.

In all write-ups I see anhydrous oxalic acid being used for KMnO titration. Theoretically I could either bake my acid and get anhydrous form or use as is and just measure it out using 126.065 g/mol weight instead of 90.03g/mol.

My burrette is a 50ml with 0.1ml divisions, so really a 1% accuracy is all I can reasonably hope for.

My question is this: Do i need to dehydrate the oxalic acid and use the 90.03g/mol weight or can i trust that most of it is in dihydrate form and I can just use the 126.065 g/mol?
Sold by Florida Laboratories, advertised as 99.6% pure oxalic. But it was a 5lb bag for $15, so hopefully its that pure...? Definitely not sure about the likely fractions of mono-hydrate and dihydrate and anhydrous...

What do you all think?
Trying to standardize KMnO for iron content determination. And really, that iron content determination only needs to be a ball-park figure, say within 5% to 10% of the reading.

[Borek]

Hydrated salts rarely have an exact composition, unless they are kept in a controlled environment (temperature, humidity). Typical procedures call for drying - like "keep for two hours at 110°C". Yous should check details though, exact temperature and time. Most analytical handbooks list such practical information, sorry, I don't have one at hand ATM.

[pcm81]

Hydrated salts rarely have an exact composition, unless they are kept in a controlled environment (temperature, humidity). Typical procedures call for drying - like "keep for two hours at 110°C". Yous should check details though, exact temperature and time. Most analytical handbooks list such practical information, sorry, I don't have one at hand ATM.

Thanks for input. No worries about the manuals; my google-fu is strong. Was mostly interested in likely composition of hydrates in the salt and you answered my question.

EDIT:
Depending on how much money i want to spend i might buy a Dean Stark Trap, or more likely i'll use KHP to standardize NaOH solution and then use that to standardize Oxalic acid solution, to then standardize KMnO.

[pcm81]

Hydrated salts rarely have an exact composition, unless they are kept in a controlled environment (temperature, humidity). Typical procedures call for drying - like "keep for two hours at 110°C". Yous should check details though, exact temperature and time. Most analytical handbooks list such practical information, sorry, I don't have one at hand ATM.

Thanks for input. No worries about the manuals; my google-fu is strong. Was mostly interested in likely composition of hydrates in the salt and you answered my question.

EDIT:
Depending on how much money i want to spend i might buy a Dean Stark Trap, or more likely i'll use KHP to standardize NaOH solution and then use that to standardize Oxalic acid solution, to then standardize KMnO.

titrated NaOH vs KHP and verified that it was 0.1M solution.
Then titrated 0.52 grams of oxalic acid vs NaOH.Consumed 83.75ml of 0.1M NaOH to get to equivalence point at pH close to 8. My closes data points were 82.5ml = 7.21pH and 83ml = 8.87pH. So interpolation yields 82.75ml to equivalence point.In turn this gives me 0.008275 moles of NaOH used to neutralize 0.52g of oxalic acid. Since oxalic acid has 2 protons that means i have half as many moles of oxalic in the sample. 0.52/(0.008275/2)=125.679g/mole. pure dihydrate should be 126.065, soo i am 99.69% ish.

Sounds reasonable or did i do any boo-boos?

[Borek]

Looks OK.