[Tex]

Hi,
I would like to do the elephant toothpaste experiment with pretty big quantities.
If I have 1l of  37,5% H2O2, how many grams of yeast do I need to turn all the H2O2 in foam?
When I add 250ml H2O to 750 ml of 50% H2O2 I have 1 l of 37,5% H2O2 right?
Can I use an empty plastic water bottle for the reaction? It doesn't get to warm when I do it in big quantities?
The foam and yeast are harmless so I'll do it in my garden so I don't have to clean all the foam.

[Arkcon]

Hi,
I would like to do the elephant toothpaste experiment

Well, that sounds OK ...

with pretty big quantities.

Annnnd, you lost me.  Why "in pretty big" quantities?  Its a pretty simple demonstration, what do you gain by making it bigger.  I mean, you can make its small, video tape it, and make the display bigger, right?  Same thing, right?  Oh, not the same thing, because its less hazardous.  Right?  OK, just so long as my objections are noted, I can keep playing along.

If I have 1l of  37,5% H2O2, how many grams of yeast do I need to turn all the H2O2 in foam?

The catalase in yeast or other living things is only needed in trace amounts.  Because its a catalyst.  Still for large amounts, it may not be in contact will all of the peroxide.  This will depend on vessel size and shape and mixing.  You'll have to think about it.

When I add 250ml H2O to 750 ml of 50% H2O2 I have 1 l of 37,5% H2O2 right?

50% H2O2 is a little dangerous for the home user.

Can I use an empty plastic water bottle for the reaction? It doesn't get to warm when I do it in big quantities?

Maybe, it really depends on how hot the reaction gets.  The more you make, the more heat you'll get.  You only notice the heat after a delay, so that can be a surprise you really don't need.

The foam and yeast are harmless so I'll do it in my garden so I don't have to clean all the foam.

I suppose so.  Reaction also produces heat and oxygen, which humans need in to keep from dying.  However, we need them in metered amounts -- that is a small amount, a little at a time.  You'll be getting lots all at once.   There's a risk of disaster, or at least, some problems.

[Tex]

I've done this experiment several times with blood, blended leaves, liver and yeast.
I want to do a big one....

The heat appears when H2O2 splits in H2O and O2 so shouldn't the heat be spread out over the foam?

One catalase molecule can convert approximately 5 million molecules of H2O2 to H2O and O2 each minute. And I suppose much of the yeast is spread out in the foam.
So I suppose the more yeast I add, the more foam I get.
There is a limit of course.

When dealing with the high % H2O2 I use goggles and gloves.