What it shows
Labels list sodium, not salt. Converting sodium in milligrams to salt in grams shows how quickly everyday snacks add up. This helps students read the label as a piece of data.
The science
Common salt is sodium chloride, and sodium makes up about 40 per cent of its mass. So salt in grams equals sodium in grams multiplied by 2.5. Sodium is needed by the body in small amounts for nerves and fluid balance, but large amounts regularly taken can raise blood pressure in many people.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Five empty snack packets or photos of labels
- A calculator
- Graph paper
- A kitchen scale and a spoon
- A teaspoon and salt
- A table for results
Safety
For this project: Use empty packets or photos only. Do not taste test salt amounts as a challenge. This is a data exercise, not dietary advice; follow your doctor’s guidance for any condition.
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.
Step 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.
Collect labels from five snack types, such as chips, namkeen, instant noodles, biscuits and papad.
Copy the sodium per 100 g and the pack weight from each label.
Convert sodium per 100 g in milligrams to grams of salt by multiplying by 2.5 and dividing by 1,000.
Calculate the salt in the whole pack using the pack weight.
Measure out a teaspoon of salt on the kitchen scale to learn that one level teaspoon is about 5 g.
Express each pack’s salt as a fraction of a teaspoon.
Draw a bar chart of salt per 100 g and another for the whole pack.
Write two sentences on what the charts show and how the pack size changes the story.
What you should see
Two bar charts that show the salt in each snack by weight and by pack, which usually reveals that some small packs have more salt than expected.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01What is the chemical name for table salt?
Sodium chloride.
02How do you convert sodium to salt?
Multiply by 2.5.
03Why look at the whole pack?
People eat the whole pack, not 100 g.
04Does this project say what you should eat?
No, it only reads labels; dietary advice comes from a doctor.
Take it further
Compare a ready snack with a homemade one made with a measured amount of salt.
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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