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Science project idea

How much salt makes an egg float?

An egg sinks in plain water but floats in salty water. Dissolving salt makes the water denser, so it pushes up harder on the egg. Measuring the salt needed turns a trick into a real experiment.

Make it yourself8 numbered steps, the materials and the science, all free.Go to the stepsGet a ready-made kitReady-made models, kits and spare parts in the store under Physics.Browse PhysicsAsk on WhatsAppAsk the head office whether a model or kit for this idea is available.Send a message

What it shows

An egg sinks in plain water but floats in salty water. Dissolving salt makes the water denser, so it pushes up harder on the egg. Measuring the salt needed turns a trick into a real experiment.

The science

Whether something floats depends on its density compared with the liquid around it. An egg is a little denser than plain water, so it sinks. When salt dissolves, it packs extra mass into the same volume of water, raising the water’s density. Once the salt water is denser than the egg, the upward push of the water is enough to lift the egg to the surface. This is why it is so easy to float in the sea.

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.

  • A fresh raw egg
  • A tall glass or a clear jar
  • Table salt and a teaspoon
  • Water
  • A spoon for stirring and a notebook

Safety

For this project: Wash hands after handling a raw egg, and do not eat the egg after the experiment.

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 rules

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.

  1. Fill the glass about three quarters full with plain tap water and gently lower the egg in with a spoon; it sinks.

  2. Take the egg out and stir in one level teaspoon of salt until it fully dissolves.

  3. Put the egg back and watch whether it floats, sinks or hovers.

  4. Keep adding one teaspoon at a time, stirring well and testing after each one, and write down the count.

  5. Note the number of teaspoons at which the egg first lifts off the bottom and the number at which it floats at the top.

  6. Once it floats, slowly pour plain water down the side of the glass and watch the egg sink to the middle, between the two layers.

  7. Repeat the whole test with sugar instead of salt and compare the number of spoons needed.

  8. Present the results as a table and a bar chart of spoons needed for salt and for sugar.

What you should see

The egg sinks in plain water, lifts off the bottom after a few teaspoons of salt and floats at the top after a few more. Plain water added on top makes the egg hover in the middle.

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 the egg sink in plain water?

The egg is slightly denser than plain water.

2What does salt do to the water?

It dissolves and makes the water denser, so the water can hold the egg up.

3Why does the egg hover in the middle when plain water is added on top?

The light plain water floats on the dense salt water, and the egg sits where the density matches its own.

4Where in nature is it very easy to float?

In very salty water like the sea, especially the Dead Sea.

Free ebook: Viva Questions for Science Projects

Take it further

Test an old egg and a fresh egg in plain water; an old egg has a bigger air pocket and may float, which is a simple freshness test.

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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