When scientists are looking for life on other planets, like Mars, there is one chemical they always look for — water. This week we will look at one reason that water is so important to life.
For this activity you will need:
Baking soda (not Baking Powder)
Cream of tartar or tartaric acid (They're the same thing. It's actually a powder)
Teaspoons
Plastic cups or glasses
Plastic food wrap (glad-wrap, cling-wrap, etc)
You probably know that if you mix baking soda with an acid, like vinegar or lemon juice, it fizzes and makes a gas called carbon dioxide. If you haven't, try it now. Mix a teaspoon of baking soda with a tablespoon or so of vinegar and watch how it fizzes.
Cream of tartar is an acid. In this activity, we are going to look at the reaction between baking soda and cream of tartar. When we mix them together, we will cover the container with the food wrap to see if there is any carbon dioxide released.
The bulge in the plastic wrap shows gas is being produced in the glass on the left.
First, lets try it without water:
In one cup, put a teaspoon of cream of tartar and a teaspoon of baking soda.
Seal the cup with the plastic wrap and give it a bit of a shake to mix the chemicals.
Watch the top of the plastic wrap. Does it bulge out at all?
Now, try it with water:
In the other cup, put a teaspoon of cream of tartar and a teaspoon of baking soda.
Pour in half a cup of water.
Seal the cup with the plastic wrap and swirl it around a bit, to mix the chemicals.
Watch the top of the plastic wrap. Does it bulge out now?
What's happening?
You should find that in the container without water, not much happens. In the container with water, there is bubbling and fizzing and the plastic wrap bulges up because of the gas being produced in the cup. To be sure that it is a chemical reaction between the baking soda and the cream of tartar, try doing the same thing with baking soda or cream of tartar separately. You should find they don't fizz at all, but just dissolve.
So why does water make the difference? The water isn't taking part in the reaction, but it is providing somewhere for the reaction to take place.
In each cup, you have two different chemicals, baking soda and cream of tartar. Each of the chemicals is made up of atoms joined together to make molecules. For them to react with each other, their molecules have to be broken apart and the atoms rearranged into different molecules.
In the dry cup, there are two things that stop the chemicals reacting:
The atoms are joined together into molecules and it is difficult to break the molecules up so they can be rearranged.
The chemicals are in tiny grains. This means that only the molecules on the outside of the grains could be involved in the reaction and only in the spots where the grains are touching. Most of the molecules of baking soda aren't touching molecules of cream of tartar, so they can't react.
When grains of powder are mixed (red and blue lumps), only a small amount of each grain actually touches its neighbour. The places where the grains touch are marked in purple. This means there are few places where the chemical reactions can occur.
When water is added to the chemicals, they dissolve. When things dissolve, two things happen:
The molecules are broken up into pieces. This makes it much easier to rearrange the molecules into other chemicals.
The broken bits of molecules are able to float around within the water, so they contact each other and react.
Even though the water doesn't take part in the reaction, without the water, the chemical reaction wouldn't happen. The same thing happens inside the cells of living things. Every living thing, plant or animal, is made up of cells. Inside the cells, there are chemical reactions, which go on all the time. Like the reaction, we have looked at today, many of the chemical reactions necessary for the cells to work couldn't occur without the water in the cells. That is one reason why scientists who are looking for life on other planets, like Mars, always try to find signs of water.
Incidentally, baking powder often contains baking soda and cream of tartar. When baking powder is used in cooking, it is mixed in with wet ingredients. This makes the chemicals in the baking powder dissolve and they produce carbon dioxide bubbles, which makes the mixture rise.
