Objective of the experiment

We want to observe which ambient favours the fermentation of yeast

Instructions

Put in three test tubes the following substances (use the same amount of each substance):

test tube # 1 : water + yeast
test tube #. 2 : water + sugar
test tube #. 3 : water + yeast + sugar

Quickly fix a balloon on the mouth of every test tube.

Observations

test tube # 1 : nothing happens
testtube # 2 : nothing happens
test tube # 3 : the balloon swells

Conclusions

The balloon swells because of the formation of a gas produced by the yeast through the fermentation. In order to ferment the yeast needs sugar.
[The gas that swells the balloon is the carbon dioxide]

BICARBONATE, VINEGAR AND BALLOONS

Objective of the experiment

We want to observe what happens stirring sodium bicarbonate and vinegar.

What to make

• Half fill a beacker with vinegar
• Pour some sodium bicarbonate in a balloon
• Fix the balloon on the mouth of the test tube
• Put the bicarbonate in the vinegar, putting the balloon upside down

Observations

Foam is formed in the beacker and the balloon swells.

Conclusions

By stirring the two substances a gas is developed like in the case of the yeast with the sugar, but in this case the balloon has swollen more because the gas is much more abundant. In some recipes, bicarbonate mixed with an acid is used instead of yeast.
[ the gas that swells the balloon is the carbon dioxide ]