How do I identify a material's physical and chemical properties? 🧑‍🔬

I'm thinking of an object you might have at home. Can you guess it?

I can hold it in one hand.

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It's yellow.

Photo by Alexey Lin on Unsplash

Its juice is acidic.

Did you guess it?

It's a lemon!

Photo by Auguste A on Unsplash

You might not realize it, but you used some of the lemon's physical and chemical properties to identify it.

Learn a little more about these key properties of materials to help you succeed in science class.

A physical property of an object can be seen or measured without changing the object's identity.

Some examples are:

• Length

• Density

• Mass

• Temperature

• Luster (shine)

Returning to our lemon example, we could measure the length of the lemon at 7.5 cm without changing anything about the lemon itself.

To get more specific, physical properties are divided into two groups: intensive and extensive.

Intensive Properties

• Don't depend on the size of the sample.

Examples:

• Temperature

• Density

• Color

• Odor/smell

Extensive Properties

• Do depend on the size of the sample.

Examples:

• Size

• Length

• Volume

• Mass (weight)

Whether we have a whole lemon or a small wedge, it will still smell like lemon. The smell is an intensive property because it's the same whether the piece of lemon is big or small.

A wedge of lemon weighs less than a whole lemon does. This extensive property changes when the samples are of different sizes.

When you observe or test an object's chemical properties, the molecules that make up the object change.

Some examples of chemical properties include:

• Being acidic or basic

• Flammability

• Reactivity at room temperature — whether it will react with water or air at typical temperatures

• Oxidation — the ability to react with oxygen

Our lemon can oxidize. If we leave it on the counter for days, it will react with oxygen and turn brown.

When you're trying to understand the chemical and physical properties of materials, discussing the changes to those properties can be helpful.

When you make a physical change to an object, its chemical composition stays the same, but something about its size or appearance changes.

Some physical changes we could make to our lemon are:

• Color — paint it blue 🎨

• Size — chop it in half 🔪

• Temperature — cool it in the refrigerator 🌡️

Photo by John Vid on Unsplash

The lemon is still a lemon after all these changes. It hasn't become something new. That's how we know the properties we changed are physical, not chemical.

Chemical changes result in new substances. Chemical properties of materials are affected by chemical changes. If you're trying to identify a chemical property of an object, it might be easier to think about how changing the property would affect the material.

Some chemical changes we could make to the lemon are:

• Burning — lighting it on fire produces ash, water, and carbon dioxide.

• Oxidation — letting the lemons react with air to become soft and brown.

• Fermenting — making preserved lemons, similar to pickling.

Photo by Jozsef Hocza on Unsplash

Chemical changes can't often be reversed. New substances have formed from the original lemon.

We've made a lot of changes to our lemon!

Let's review:

Physical Properties

• Observed without changing the material

• Can be intensive (don't depend on sample size) or extensive (depend on sample size)

• Include size, mass, density, temperature

Chemical Properties

• Testing them changes the chemical makeup of the object

• Aren't easily reversed

• Include flammability, oxidation, reaction with acid or base

Devon is trying to figure out the physical and chemical properties of a wooden log they found in their shed by doing different tests. Could you identify the chemical properties that Devon tested? How they tried each is noted in parentheses.

Now, that's a chemical change for ya!

Apply what you learned about physical and chemical properties of materials: