oxalic acid titration

I have to write a lab report from practical session we had last week. The thing is: I don't understand what I have to do or rather how to do it.

"In this experiment you will use the traditional method of titration to determine the number of moles of water of crystallization in solid crystals of ethane 1,2-dioic acid which has the formula (COOH)2 * xH2O"

and I don't know how to do it.

during the lab we titrated the acid into NaOH (known concentration and volume). so my result was a volume of acid titrated until the equivalent point.

but what am I supposed to do with this volume?? how to calculate the amount of water of crystallization??

please, can anybody help me?

Reply 1

oceane

I imagine you weighed out accurately a quantity of hydrated oxalic acid crystals and diluted this, maybe making up a solution to 250cm^3 in a volumetric flask. Is that right?

You then pipetted samples of this aqueous oxalic acid (maybe 25cm^3) into a flask to titrate them. Is that right?

2 moles of NaOH react with every mole of oxalic acid. So you work out how many moles of NaOH there were in your average titre and therefore you know there were half as many moles of oxalic acid in the pipetted sample.

You then work out how many moles of oxalic acid in total there will have been in the solution you made up in the volumetric flask.

You know the molar mass of (COOH)2 (90g per mole) so work out the mass of oxalic acid in your volumetric flask.

The difference between that mass and the initial mass of crystals you weighed out is due to the water in the crystals. Knowing that water has a molar mass of 18g per mole, you can now work out what x is.