Fizzing and improvised test tubes

We have got through a lot of tubes of bubble mix this summer as I was tempted to buy a big multipack because it was the same price as a four-pack. Aside from both boys having lots of fun popping bubbles, and using some of the mix for our bubble snakes and different shaped bubble wands, we've accumulated lots of empty bubble tubes.  I thought they might make appealing test tubes for some garden chemical reactions, so I made a quick rack for five from a cardboard box that was heading to the recycling.  

Improvised test tubes

You'd get greater stability from a deeper box than the one I used, but it's what we had to hand.  I just cut a cross shape with a Stanley knife on one side of the box for each tube, and pressed the four corners in.  This worked remarkably well, and although it got pretty soggy whilst being used, on a hot summer day it dried out and we used it a second time (and it's still fine to use again before it eventually gets recycled).

Carbon dioxide bubbles

I went for a simple setup for my son as he's enjoyed making things fizz recently, and just put out some diluted vinegar (about one part in four parts water) in an empty yoghurt tub and a little pot of bicarbonate of soda with a strip of cardboard to use as a spatula.  I would have used a spoon but I feared his little brother (19 months) would be tempted to eat the bicarb as it would look too much like food!  We have some children's pipettes so I gave him one of those to transfer the vinegar to the test tubes - he likes using these as it makes him feel like a real scientist!  He also wore goggles as we have them, but if you don't then you probably want to put this setup on a table where the child doesn't lean right over the top of it - the reaction can go pretty fast and shoots up and out of the tube even with diluted vinegar.

I put all of this in a plastic box in the garden, and suggested he try mixing the vinegar and bicarb in the tubes.  The reaction between the acetic acid (vinegar) and sodium bicarbonate produces carbon dioxide, and the bubbles are easily visible in the coloured tubes.  He found it fun to try and get the quantities right so the bubbles came out of the top, but didn't spill over the side - he had fun experimenting with putting in more or less vinegar and more or less bicarb.  I enjoyed watching and listening to him figuring out for himself when either the vinegar or bicarb was rate-limiting (i.e. if he added more then he saw more bubbles) and that if he added more of both then he made more bubbles.

Using the cardboard spatula

The smaller one was very interested in what was going on, although he doesn't really have the fine motor skills yet to do this activity.  The big one helped him squirt a bit of vinegar in a tube, and after a bit of a dispute about whether the tube was going to stay in the cardboard rack, I found him another tube to play with whilst the original filled with vinegar stayed in place for further experimentation!  

I think I'll be asked to get this out again sometime soon as my son liked his garden lab, and doesn't seem to tire of making things fizz!