Science Week @ Glenbrae School

This week we have been focusing on Science. Room 7 students have been moving around all the senior classrooms learning with the different teachers about chemical changes. 

Also each class has come to Room 7 to learn about the chemical change that happens when you bake bread using yeast or baking soda. 

We followed the scientific process and practiced asking questions and hypothesising. 

We asked How does yeast make bread rise?

We hypothesised that Heat and time make the yeast rise/produce gas. 

We observed a lot of things with the bread making process. We observed the yeast foaming, it looked like oatmeal/porridge and smelled yuck - like beer! 

When we added the flour, we all got to help knead the dough and feel the elastic-ness of it. It turns out that some of us have the potential to be master bakers and were very good at this step. 

Once we had kneaded the dough, we decided to test our hypothesis and split the dough in two. One part of dough was set aside to rise (time) as per the recipe, and the other dough was put straight in the oven (heat) to rise and cook. 

Meanwhile we did another experiment using two plastic bottles and balloons.

In one bottle we put a mixture similar to the bread (1tbsp yeast, 1/2 tsp sugar and 1 tbsp warm water), and put it aside for an hour on the sunny windowsill

In another bottle we put a vinegar and baking soda. 

What we observed was that both balloons blew up, filled up with air. But how could the air get into the balloon, while it was sealing the top of the bottle? It was a chemical change. 

The vinegar and the sodium bicarbonate mixed and the elements changed their chemical bonds to create different chemicals. 

CH3COOH + NaHCO3  → CH3COONa + H2CO3

vinegar + baking-soda (sodium bicarbonate) → sodium acetate + carbonic acid

We created sodium acetate and carbonic acid. But the carbonic acid isn't very stable on its own and breaks down into carbon dioxide and water, we could see the bubbles of the carbon dioxide.

H2CO3  → H2O + CO2

carbonic acid → water + carbon dioxide

 We discovered that is a living organism that needs sugar to react. Together they change into water, H2O, and alcohol (just a little bit - which burns off in the baking process).

We also observed that the two breads we baked were very different.

The bread that went straight into the oven was smaller, denser (more tightly packed) and had a slightly sweet/sour taste - probably from the under-developed yeast.

The bread that was allowed to rest before baking was lighter, less dense and had little air holes throughout from where the carbon dioxide had formed. It also didn't have the sweet/sour taste like the other one. This was our favourite.

To enjoy our bread we also made fresh butter from shaking cream and a pinch of salt in jars. We were left with lovely soft delicious butter and a milky liquid called 'buttermilk'.

Stay tuned to our personal blogs for actual photo's of the experiments that we conducted throughout the week.