endo and exo reactions

[pkij]

Does anyone have a list of endo and exo reactions suitable for junior science?
Thanks

Probably should add reactions that work and do produce a temp change that is reasonably obvious!!

[lada]

We just did some with yr9.
Dilute HCl and Mg ribbon and

dissolution of following substances in water:
anhydrous CaCl2
KCl, NaCl,NaOH and KNO3
Let them do it in styroform cups with lids on them and insert thermometer throught the lid.
make sure they take initial temp then completely dissolve the substance and take temp.
Lada

[smiley]

Can't beat Thodium THiosulphate for a really good endo experiment. Mind you a drop of meths on the back of the hand is a good place to start, for embracing the concept of endothermicity! (I made that word up - good eh?)

Cheers, K

[lada]

Our teachers are sticklers for safety and sodium thiosulfate with HCL gives off supfur smell, so they will only do it in fumecupboard, so I only give it to senior students now. But you are right, it is an excelent example.

[Ross]

One of the best endothermic reactions is the barium hydroxide (solid) added to ammonium thiocyanate (solid). A liquid is formed, ammonia given off and any water on the outside of the reaction vessel freezes. Its a shame that it uses some nasty chemicals.

A far safer endothermic reaction is using citric acid and sodium bicarbonate. I have achieved a drop in temperate of about 5 degrees in a beaker with the method below. (all done in a few minutes)
1. add a teaspoonful of citric acid to 100mL of water
2. record the inial temperature
3. add a teaspoon of sodium bicarbonate
4. note the temperature drop - the reaction is finished when the fizzing stops

Cheers

[lada]

Hi Ross, that is cool. Our chem teacher did it and beaker froze to the mat.
Also the safe one is very distinctive, about 5-6oC drop in temp.
Just for that, karma is coming your way

[smiley]

Ha! Cool! How apt.

Cheers, K

[estelle]

Does anyone know the exact amounts of barium nitrate and ammonium thiocyanate to get the freezing result? For endothermic reaction for Year 10 demo.
Estelle

[rae]

Hi,

8g ammonium thiocyanate (NH4SCN) in to a 250ml conical flask stoppered
16g barium hydroxide(Ba(OH)2.8H2O into another container
Add Ba(OH)2 to NH4SCN stopper and shake vigourously until crystals start to liquify.
Place flask on a block of wood in a small pool of water Leave about 10 mins(should freeze the water).
Test liberated gas with red litmus (NH3 gas)
Hope this helps
Lorrae

[Ian]

You learn so much here!!!

I always thought it was a "largish scoop of Ammonium Thyocyanate and a decent shake of Barium Hydroxide"

I think we determined last year that Potassium Permanganate and Glycerine was still OK for Exothermics, didn't we? Again my measurements have always been "a medium size pile of KMnO₄ and a decent slurp of glycerine" Anybody got a more precise measurement than that?

regards
Ian

[lita*]

Hi!
Where are you sourcing your Sodium (Thodium) Thiosulphate from? Its not available fom Q stores.
It took 6 months to get an order from Silform for it and by then my senior had cancelled the order.

[labman]

Hi Lita,
I get mine from Omega Scientific, our main school supplier in S.A. It's about $12.00 for 500g container. Contact is James Willmore, Ph (08)82894311.
Cheers,
Lisa