Pure Substances and Mixtures

AZ State Standards

• Concept 1: Structure and Properties of Matter • Understand physical, chemical, and atomic

properties of matter. • PO 1. Describe substances based on their

physical properties. • • PO 2. Describe substances based on their

chemical properties. • PO 4. Separate mixtures of substances based on

their physical properties.

Content Objectives

• SWBAT differentiate between pure substances and mixtures by examining whether they can be separated by physical means.

• SWBAT determine the type of mixture by physical properties and whether they separate over time.

Pure Substances

• Substances that contain only one type of element or compound.

Quartz crystals made of pure silicon dioxide (SiO2)

Pure Substances

water salt (sodium chloride)

rust (iron oxide) sugar (glucose)

Mixtures • Containing two or more different substances

• Containing multiple types of compounds or elements

Types of Mixtures

• If it is distributed equally it is homogenous.

• If it is unevenly distributed, it is heterogeneous

Mixtures Can Be Separated by Physical Means

• Think about what kinds of physical ways you could separate two substances.

Heterogeneous Mixture • Particles are large enough to be seen, or not

mixed thoroughly enough so that textures and colors can be discerned.

Homogeneous Solution

• Small particles so evenly mixed that individual particles, textures, or colors can not be determined.

Solution • A homogeneous mixture involving an

electromagnetic interaction between molecules.

• Solutions are by definition transparent.

They can be colored, but if you can see through them they are a solution

Colloids • Particles are small enough that they remain

suspended indefinitely.

• But, they are large enough to deflect light making them opaque.

Fog is a colloid of water droplets mixed in air

Milk contains fat droplets in water

Suspension

• Substances separate out over time due to differing densities.

Mud will settle out of water

Oil is less dense than vinegar and rises to the top

Dust will settle out of the air

Can be homogeneous or heterogeneous depending on the particles involved

Precipitate • Precipitates are solids that form during a

chemical reaction between two solutions.

Mixtures • Iron and Sulfur powder in a the mixture

• So, it is hypothesis time:

How can we separate the iron from the sulfur?

Remember, Mixtures Can Be Separated by Physical Means

• Think about what kinds of physical ways you could separate two substances.

Mixtures

• How can we separate the iron from the sulfur?

• Use a magnet!

• Iron is magnetic, sulfur is not...

Mixtures • How can you separate the salt and water?

• So, it is hypothesis time:

Evaporating the Water Off

• Using a change in the state of matter of one, the water turns from liquid to gas, but the salt remains a solid.

But, What If You Want To Keep Both the Salt AND Water?

Chemical Compounds Are Not Mixtures; They Are Pure Substances

• When two substances combine chemically, they become a new pure substance that can not be separated by physical means.

Turning an iron-sulphur mixture into a Compound

Fe + S FeS Heat

Compounds form as a result of chemical reactions

When iron and sulfur react

+ sulfur (S) atoms iron (Fe) atoms

When iron and sulfur react

+ sulfur (S) atoms iron (Fe) atoms

iron sulfide (FeS) molecules

Iron Sulfide is Not Magnetic

• They can not be separated into iron and sulfur through any physical means.

Differences between compounds and mixtures

MIXTURES COMPOUNDS

1. Mixtures can be separated easily

1. Compounds can not be separated

Differences between compounds and mixtures

MIXTURES COMPOUNDS

1. Mixtures can be separated easily

2. Mixture have the properties of the substances present in it

1. Compounds can not be separated

2. Compounds do not have the properties of the elements

Differences between compounds and mixtures

MIXTURES COMPOUNDS

1. Mixtures can be separated easily

2. Mixture have the properties of the substances present in it

3. No chemical change takes place when a mixture is made

1. Compounds can not be separated

2. Compounds do not have the properties of the elements

3. A compound is always formed due to a chemical reaction

Differences between compounds and mixtures

MIXTURES COMPOUNDS

1. Mixtures can be separated easily

2. Mixture have the properties of the substances present in it

3. No chemical change takes place when a mixture is made

4. There is no heat taken in or given out when a mixture is made

1. Compounds can not be separated

2. Compounds do not have the properties of the elements

3. A compound is always formed due to a chemical reaction

4. Heat is either taken in or given out when a compound is made

Differences between compounds and mixtures

MIXTURES COMPOUNDS

1. Mixtures can be separated easily

2. Mixture have the properties of the substances present in it

3. No chemical change takes place when a mixture is made

4. There is no heat taken in or given out when a mixture is made

5. A mixture can contain elements in any proportion

1. Compounds can not be separated

2. Compounds do not have the properties of the elements

3. A compound is always formed due to a chemical reaction

4. Heat is either taken in or given out when a compound is made

5. A compound always contains the elements in fixed proportions, e.g. FeS contains 7g of iron to 4g of sulphur

Content Objectives

• SWBAT differentiate between pure substances and mixtures by examining whether they can be separated by physical means.

• SWBAT determine the type of mixture by physical properties and whether they separate over time.