What it shows
Baking soda needs an acid to give carbon dioxide, while baking powder already has its own acid and only needs water. Testing both with vinegar, curd water and plain water shows why recipes pick one or the other.
The science
Baking soda is sodium bicarbonate, a base. When it meets an acid it makes carbon dioxide, water and a salt. Baking powder is baking soda mixed with a dry acid and starch, so adding plain water is enough to start the reaction. The gas is what makes a cake soft and light.
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.
- 1 spoon of baking soda
- 1 spoon of baking powder
- Small clear glasses, 6
- Plain water, vinegar, and diluted curd water
- A measuring teaspoon and a ruler
- Small balloons, 6, to catch the gas
- A marker pen
Safety
For this project: Do not taste the test glasses. An adult must supervise the balloons so no fizz goes near the eyes, and wash hands after the test.
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
7 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.
Label six glasses with the combination to test: soda in water, soda in vinegar, soda in curd water, powder in water, powder in vinegar and powder in curd water.
Put one level spoon of baking soda or powder in each glass as labelled.
Pour three spoons of the right liquid into each glass at the same moment, starting with the glass you want to watch.
Quickly place a balloon over each glass mouth and watch it inflate.
Measure the foam height or the balloon size across the middle in centimetres after one minute.
Record all six readings in a table.
Rank the combinations from most gas to least gas.
What you should see
Baking soda gives strong fizz only with vinegar and a little with curd water, giving almost none with water. Baking powder fizzes with all three liquids, showing that it carries its own acid.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why does soda need an acid?
The reaction that gives carbon dioxide takes place between a base and an acid.
2Why does powder fizz in plain water?
It has a dry acid mixed in that dissolves in water and starts the reaction.
3Which gas is made?
Carbon dioxide.
4Why do some recipes use curd or buttermilk with soda?
Curd is acidic, so it gives the soda something to react with.
Take it further
Bake two small idlis or cakes, one with each, and measure which one rises more.
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.
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