Australia's Science Forum

Morning everyone!!

Yr 7 do a crystallisation prac using soft drink and evapourating this in dishes over a bunsenuntil most of the water is evapourated. They thenleave it to cool and presumably sugar crystals form. We have never had any success with this prac. The kids either burn the sugar or no crystals form.
Does anyone have any suggestions on improving this prac or can suggest another prac to do that will work better??

Thanks Lorrae

Know what you mean! you have a syrup not crystals, we do that prac to see how much sugar is in a can of soft drink.
For crystalisation, we use copper sulphate waste or salt water.

Well coming from sugar country I know that CSR and other associated sugar mills pay big money to somebody to crystallise their sugar after processing. It's not as easy as salt! Sugar holds SO much water that you just end up with more and more concentrated sugar gloop, and no crystals. So, apparently, it's a rare art.

Unless of course you are trying to make toffee, or creme brulee topping. Then the sugar won't stop crystallizing!

Cheers, K

One of my teachers tried to recrystalise sucrose. Because it doesnt get saturated so much as turn to syryp, the class ended up using over 3 kg of sugar, and still didnt get any sugar crystals.
I played around a bit and came up with something that sort of works. You have a test tube of the syryp in a hot water bath-super duper saturated. Get the students to smear a bit on a slide and then look at it under a microscope. If the syryp was strong enough then it will crystalise. It does take a little while, but the light of the microscope helps the process too.
I have done this with a range of salts and it works brilliantly. We have a camera which connects the micrscope to the TV-I think its called Flex-Cam. I have even been able to video it for classes to watch. You get the see the shapes really well. With the salts it is actually better if the solution isnt quite saturated as the crystals form too quickly and they squash into each other.

Pat

Pat,
What a clever idea!!!! Can you actually see the crystals growing? I think I will have to try that one. Who cares if the kids (or teachers) are interested or not. It sounds like a LOT of fun!!!
Thanks
Ian

Hi all!
Some teachers still use copper sulphate. Most are using Borax and pipecleaners to grow crystals. I brought this prac back with me from a day at St Mary's and it goes down really well.
Cheers
Rita

hi Rita, Would love a copy of that experinment, do'nt remember that in St Marys last year, perhaps it was from another year?????????

Fax number 9823 7662 attn Sue in Science

We have 2 digital video cameras mounted on microscopes - the Chemistry teacher did a prac making crystals in petri-dishes and we videoed tham .. fascinating to actually see the crystals form. We used a dataprojector and the whole class could see the process happening

Do you watch the videos in real time or play them in FF? Just wondering if it would work with the microscope simply connected to the TV with our videoflex as we don't have a recorder.

I like the sound of the crystallisation of the borax with the pipecleaners. It would probably appeal to the Year 7 teachers here. Would you mind sending me a copy of the prac. Thanks heaps.
Robyn (Science)
Fax: 66222940

Yes Rita,

Could I please have a copy too?

Fax: 02 6762 1264

Rather than everyone requesting fax's of pracs maybe we should have a spot on forum where they can be posted. and everyone can access as an attachment and download!

HI,
My school uses salt, sugar, copper sulfate but they use fertilizer that has a high content of urea mix it in hot water and add colour to it with food dye then in a plastic dish the children have cut out of carboard tree sticky tape it down and add the solution they have made. You leve this for a few days and it grows cystals on the tree the kids love it.

Pat's idea sounds brilliant!
At my school they make crystal crowns which work really well. They cut filter paper to make a little crown ( like the kids make for Christmas plays), forming a cylinder. They make a saturated solution of salt water and then add some food colouring. Pour the solution into a petrie dish and stand the crown in it. After a couple of days in a cool place the crystals have grown on the crown and, depending on the colour used, you have a great example of chromatography.

We also have an exchange teacher who did rock candy with her class. Made coloured super saturated sugar solution ( 2 parts sugar to 1 of water). They poured the sugar soln into jars the students had brought from home and they used a wooden skewer or tied a weight to string and suspended it into the solution. Leave to crystallise and you have something for the darlings to eat. That's always a hit!

Sharon

Hi Sharon,
Thanks for the great crown idea. I gave it a try yesterday with a saturated solution of alum and mixed food colouring. Separation of colours was evident within 10 minutes as they travelled up the crown. This morning when I arrived I was greeted with beautiful "gold" crowns with purple spikes and blue "gem" on the tips! They are fantastic! The surface is dotted with mini crystals. I was most impressed. Sent you some Karma for your great idea
Jen

Rita, hi Vicki at Murrumburrah High, would you mind faxing me a copy of that experiment too.
Fax 02 6386 3048
Thanks heaps Vicki

Thanks Pommy for the reality check!
Silly me, thinking you can exchange info without being sued,
Oh well only 5 years to hang-in there till permanent school holidays

Do not know anything about being sued, only trouble.

Hi All,
I have posted the prac using Borax under the Recipe Heading.
Sorry for not posting earlier...I couldn't find it. (It was hiding in right folder, wrong section!)

Rita

Many thanks indeed Rita for tye Yr7 Crystallisation prac, it is good.