Australia's Science Forum

this prac is from 'about science 4' page 230 - where you drop the HCL into a beaker and it changes colour.
I rememebr doing this the first term i was here (2 yrs ago) but cannot get it going this time

anyone done this? know what I am talking about???
HELP???

I don't know which experiment you are talking about. I just made a rainbow in measuring cylinder by pouring saturated sodium carbonate slowly into a 100mL measuring cylinder that was filled with 0.1M HCl and universal indicator. Its to show density and diffusion.

We use 250mL 0.1M sodium thiosulfate and 5mL 2M hydrochloric acid and sit it on an overhead projector. As the solution heats up the reaction goes from clear through to black as the sulfur precipitates out. Called the Sunset Reaction because of the colours. We use it to demonstrate colloids.

Thanks!!!

We got it working!, the etxt book didn't say molarity of anything, so we fiddled around and got it.
At first we were using a ray box, but i believe it worked on the overhead better!

Na₂S₂O₃ (aq) + 2 HCl (dil aq) → 2 NaCl (aq) + S (coloid) + H₂O (l) + SO₂ (g)

It's known as a "clock reaction", because it leads to an abrupt colour change after a period of time has elapsed, based on crossing a concentration threashold.

Use for classic rate of reaction experiments, to show/measure how temperature and concentration effect the rate. Use 2M HCl and 0.25M sodium thiosulphate.
The two chemicals react to form a sulphur colloid makingthe solution cloudy. The time taken for the precipitate to obscure a cross marked on a piece of paper placed under the reaction flask is used as a measure of reaction rate.

Our yr 12 use this for planning investigations. Science World 9 gives instructions for temperature.
It is one of my favourites because it can be guaranteed to "behave".

Rosalie (another one)