Australia's Science Forum

Just wondering if anyone knows of a prac where you add something to a beaker (containing water or some other colourless liquid?) and then it turns black and then you add something else and it turns clear again. Not much of a starting point but I have been asked about it by someone who remembers seeing it when they were at school and wants to know what it was! I don't know if the things you add are solid or liquid or what!!!

Rosalie,
there is one experiment out there which is water to wine and back again using phenolphthalein.........
Robyn

that sounds like the one that was demo'd at the science conference on the friday morning, but i didn't write the substances down...anyone???

Oh this is right up my street!

Get yourself 2 jars/reagent bottle etc with screw top lids - 1 clear and 1 amber. In the clear jar add a couple of drops of NaOH, in the amber add a couple of drops of Phenolphthalein. Swish them around a bit so they're all over the sides of the jar. Use a glue stick to put a bit of glue on the inside of the lid of the bottle. Sprinkle some dry citric acid crystals onto the glue.

Now, give the kids a spiel about here are two clean jars, you just rinsed them out etc etc (thus explain the drops inside them). Add water from the tap to the clear jar. Pour the clear "water" into the amber jar. Count to ten, say hocus pocus, whatever. Pour the liquid back into the clear jar. It's now pink - i.e. "wine". Announce that you are now teetotal and don't wan't wine. Screw on the lid and shake. The liquid is neutralised by the citric acid and goes back to clear. Yay!

Just do search for phenolphthalein. You will get the water to wine recipe under the heading of Science week dated about June 2008.
Lyn.
P.S. To turn wine back to water add a clear acid solution. Sorry can't help with strengths at the moment as my folder with good demos to do is at home at the moment.
P.P.S. Smileys demo sounds really good.

Another colour change one to do for science fair ect.
Blue Bottle
Dissolve 12g of glucose (powder) in a litre of water (volume not critical)
Within an hour of class time dissolve 12g sodium hydroxide in the glucose solution. Add about 1mL of methylene blue solution to produce a blue color.
Stopper the bottle.
After the solution has been left to stand the blue color will fade to yield a colorless solution.
Shaking the flask will cause the solution to turn blue.
The blue color fades rapidly (depending on the degree of agitation when the flask was shaken) and returns on subsequent shakings.

Technical stuff
On shaking, oxygen dissolves in the solution and reacts with methylene blue to give a blue color (methylene blue in an oxidised form)
On standing, alkaline glucose acts as a reducing agent and the methylene blue is reduced to a colorless oxidation state.

Sounds like the Clock Reaction to me.
Post your fax no. and I will send you a copy...it is great fun

OOOOOh send it to meeee tooo (08) 89830333 Pleeease

Thanks everyone for the suggestions - I had thought of the phenolphthalein one but the one described to me was black, not pink... I especially like smiley's one!

Judy R, my fax number is 02 6762 1752. I'm not sure that is the one I am after but I can have a look.

Thanks again, everyone! I'd be glad for any more suggestions as well

PS please mark Attn: Rosalie Murray (so it gets to the right Rosalie - there are two of us working here!)

I faxed the Clock reaction to the two who requested it.
Please post acknowledgement when you receive it

Got the fax Thanks Judy. I'll have a look at it.

Thanks Judy! I haven't hauled my butt down to the office to check my pidgeon hole but im sure it's there Thanks Again!

Hi Rosalie,

Just a quick one for you, and I will list the reagents required then give you the steps.

Methylene blue
Sodium Hydroxide (250mL)
Glucose
Flask
Stopper to fit flask.

Add 5gms of Sodium Hydroxide to the flask

to this add 5grams of glucose.

then to this mixture add a small out of Methylene Blue to colour the solution blue (Not too much or it will go black)

add approx 125mL of water (tap water is fine)

Stopper then shake the liquid, this will turn blue then change to clear again upon settling (15 seconds) then shake again to repeat the process, you can do this all period long.

Cheers,

Robb.....

Hi all,

sorry for the possibility of repeating I did not see the previous posts.

If you are not familiar with this one, try it.... if so disregard this message.

Cheers,

Robb.....