What it shows
Baking soda and vinegar react to make carbon dioxide gas, which inflates a balloon fitted over the bottle. Using more baking soda makes a bigger balloon, until the vinegar is used up and extra baking soda does nothing.
The science
Vinegar contains acetic acid and baking soda is sodium bicarbonate. When they meet, the acid and the bicarbonate swap partners and release carbon dioxide gas, water and sodium acetate. The gas has nowhere to go but into the balloon. Each spoon of baking soda can only react with a fixed amount of vinegar, so once the vinegar is finished, more baking soda cannot make more gas.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Baking soda, 4 teaspoons
- Vinegar, 1 cup
- Four small plastic bottles of the same size
- Four balloons
- A funnel made from paper
- A measuring tape or string to measure the balloon
- Teaspoon
Safety
For this project: Do the activity on a tray; vinegar stings eyes, so do not rub eyes until hands are washed. The balloon only inflates and will not burst.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Pour a quarter cup of vinegar into each of the four bottles.
Using the paper funnel, put half a teaspoon of baking soda into the first balloon, one into the second, two into the third and four into the fourth.
Stretch the mouth of each balloon over its bottle neck without letting the powder fall in yet.
Lift the first balloon so the powder drops into the vinegar and watch the fizzing and the balloon swelling.
When the fizzing stops, wrap the string around the fattest part of the balloon and measure the length against the tape.
Repeat for the other three bottles, measuring each balloon at its widest.
Draw a chart of balloon size against spoons of baking soda.
Notice that the fourth balloon is hardly bigger than the third, and look for undissolved powder left in that bottle.
What you should see
Balloon size grows with the amount of baking soda up to about two teaspoons, then stays the same, with leftover white powder in the bottle that had four spoons.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Which gas fills the balloon?
Carbon dioxide.
2Why did the biggest spoonful not give the biggest balloon?
All the vinegar was used up, so the extra baking soda had nothing to react with.
3Is this a chemical change?
Yes, new substances are formed: a gas, water and a salt.
4How can you tell a gas was made?
The balloon inflated without anyone blowing into it.
Take it further
Keep the baking soda fixed and change the amount of vinegar instead, and find the pair that gives the biggest balloon.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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