Lesson 5: Pure Substances and Mixtures

Are colloids homogeneous or heterogeneous?

Colloids are heterogeneous because they are not uniform throughout.

Is distilled water a mixture or a pure substance?

Distilled water does not have salts or silt in it. It is a compound made from atoms of the elements oxygen and hydrogen. A compound is a pure substance.

What do you call separating water into its component elements, hydrogen and oxygen, and how is it done?

Electrolysis is the process of separating water into hydrogen and oxygen. It is done by passing an electric current through the water.

What are some examples of colloids that include a gas and a liquid?

Fog and mist are colloids composed of water vapor and air. Aerosols, such as hairspray and deodorant, are composed of chemicals and a gas propellant.

What are some examples of homogeneous mixtures?

Homogeneous mixtures look the same throughout. Some examples are iced tea, soda without bubbles, salt water, coffee, and vinegar.

Why is hydrogen a pure substance?

Hydrogen is a pure substance because it is an element.

What are some examples of heterogeneous mixtures?

In a heterogeneous mixture you can see the component parts, or they settle out after a short time. Some examples are salad dressing, vegetable soup, and pizza.

Why is salt a pure substance?

Salt is a pure substance because it is a chemical compound and its elements can only be separated by chemical means.

Why aren't powdered mix drinks or saltwater pure substances?

Powdered mix drinks and saltwater are mixtures. They are not made of a single element or compound.

What are some examples of colloids that include a gas and a solid?

Smoke, smog, and air pollution are composed of small particles suspended in the air.

What are some examples of chemical changes?

Some examples of chemical change include burning wood, rusting iron, and dissolving metal by using a strong acid.

Do two compounds form a mixture or a pure substance when you put them together mechanically, such as by stirring?

They form a mixture

Is rainwater a pure substance or a mixture?

Water vapor that rises to form clouds is a pure substance. But raindrops form around tiny particles of dust; when they are large enough they begin to fall. So rain is actually a mixture, not a pure substance.

How is a colloid different than a suspension?

While colloids and suspensions are both heterogeneous mixtures, colloids are different than suspensions because their particles will not settle out.

How could you separate a mixture of sand and water?

You could wait until the sand settles to the bottom of the container and then drain off the water. Or you could use a filter and pour the mixture through it. If you wanted to drink the water, you should probably do both.

What is a pure substance?

an element or compound that cannot be separated by physical changes.

What are some methods for physically separating a mixture?

can be separated by straining, filtering, magnetizing, and settling.

What is the definition of compound?

is a substance made up of atoms or ions of two or more different elements joined by chemical bonds.