Substances and Mixtures!

Substances:

Matter – everything that has mass and takes up space.

It can be classified by its physical properties.One way to classify matter is based on its chemical composition.

Matter that has the same composition and properties throughtout is called a substance.

There are two types of substances –elements and compounds.

Substances:

Remember that elements are substances made up of only one type of atom.

Different elements can combine to form new substances called compounds.

Compounds are two or more elements that are chemically bonded together.

Substances:

Compounds can be broken down only by chemical means in to the elements that combined to make them.

For example, boiling, freezing, stirring or filtering will not separate the hydrogen atoms from the oxygen atoms of water.

However, if electricity is added to water, it can be broken down into hydrogen gas and oxygen gas.

Mixtures:When two or more substances come together but don’t chemically combine or bond to make a new substance, a mixture results.

Unlike compounds, the proportions of the substances in a mixture can be changed without changing the identity of the mixture.

For example, if you put some sand into a bucket of water, the sand doesn’t chemically combine with the sand and water.

Mixtures:

Physical properties can be used to separate mixtures into simpler substances.

The solid sand can be filtered from the liquid water using a sieve.

Homogeneous Mixtures:

Homogeneous means ¨the same throughout.¨

Homogeneous mixtures contain more than one substance evenly mixed but not chemically bonded together.

You can’t see the different parts in a homogeneous mixture no matter how closely you look.

Homogeneous Mixtures:Homogeneous mixtures can be solid, liquid, or gas.

The brass in a trumpet is a solid mixture of zinc and copper –two elements.

Sugar water is a homogeneous liquid mixture of water and sugar –both compounds.

Air is a homogeneous mixture of elements: nitrogen, oxygen, argon, neon, and helium –and two compounds: carbon dioxide and water.

Homogeneous mixture is also known as a solution.

What is the difference between a substance and a homogeneous mixture?

The difference between a homogeneous mixture and a pure substance is that a pure substance has a fixed composition and cannot be separated because it is chemically bonded and a homogeneous mixture can be separated.

Heterogeneous Mixtures:A hererogeneous mixture is one of two or more substances that are not mixed evenly.

You can see the different parts of a heterogeneous mixture, such as a mixture of sand and water.

A pizza is a heterogeneous mixture.Other examples include salad, a bookshelf full of books, or a toolbox full of nuts, bolts, screws, nails, and tools (etc.).

Questions…

What is the difference between a homogeneous and a heterogeneous mixture?

How are substances different from homogeneous mixtures?

The end!