In this video we will prepare oxalic acid using an old-fashioned preparation

which uses nitric acid to oxidize cane sugar. We're just using regular

granulated cane sugar which is near enough pure sucrose. Weigh out 10 grams

of sugar. Transfer this into a large 250 ml conical flask. Now measure out 50

mils of concentrated 68% nitric acid. Transfer this into the flask containing

the sugar.

If you use a beaker for the reaction, be warned that the mixture will bubble and

spit and may cover the area in acid spray. Give the flask a swirl for a few

minutes and you'll see all the sugar dissolve in the solution. But there's no

reaction yet.

Place the flask on a hot plate and very gently warm it. You're aiming for a

temperature of about 70 degrees C.

At about 40 to 50 degrees you'll see a yellow

color and some brown nitrogen dioxide gas produced. The mixture gradually gets darker

and suddenly you'll see a few bubbles in the mixture. This is the reaction starting

up. Get your strong ventilation switched on. Within seconds the mixture starts to react

vigorously and a lot of nitrogen dioxide is produced. This is extremely toxic so take

care and use strong ventilation.

The reaction is strong but doesn't get out of control as you can see. Once the reaction

starts, switch off the hot plate as the heat generated will sustain the reaction. After

about 10 minutes the reaction dies down a bit. At this point switch the hot plate back

on again and keep the mixture boiling and slowly evaporating.

Nitrogen dioxide gas.

It continues to be evolved and keep the evaporation going until you are down to

about 30 mils of liquid.

At this point transfer the hot liquid into a beaker for faster evaporation.

Now return to the hot plate and evaporate down by half until around 15

mils remain.

Some nitrogen dioxide continues to be evolved during this period as you can see.

Up to seconds of abruptly lawsuit.

Once you reach this point measure out 15 mils of water.

Add this to the boiling acid mixture.

And now reduce the mixture down again on the hot plate.

A small amount of nitrogen dioxide will be formed now but not much.

The target is to get down to about 10 mils of liquid remaining.

This is about right.

Once you are there allow to cool slowly.

You'll quickly tell the dzięki that the liquid has evaporated.

see crystals forming and after chilling for a while you'll end up with a slush

of crystals in the beaker transfer into a filter we've used a

glass center for this but you could use a filter paper just as well you'll need

a filter for a while in order to get all the liquid off the crystal then allow

the crystal to dry thoroughly on the filter here's the product 4.8 grams of

oxalic acid dihydrate if sucrose can potentially yield to molecules of

oxalic acid due to it being comprised of glucose and sucrose then this is a 65%

yield you can purify this further by

recrystallizing from hot water you can also dehydrate in an oven at

120 degrees celsius

to give the anhydrous acid stay tuned for more videos