Substances, Mixtures, Solubility

Chapter 21

Section 1: Substances

•A substance is matter that has the same fixed composition and properties.

•Identity can be changed by chemical processes but not by physical processes.

Elements

•An element is an example of a pure substance, it can NOT be broken down into simpler substances.

Compounds

•A pure substance composed of two or more elements that chemically combine.

Compounds

•Compounds also have fixed compositions.

•The ratio in a compound is always the same.

•Example: Water

Join in definite ratio

•Ratio is according to the mass sizes.

•Water is hydrogen and oxygen

•1 gram of hydrogen for every 8 grams if oxygen

•1:8 mass ratio of hydrogen to oxygen

To Form a Compound

•The atoms must chemically combine through a Chemical Change!

•Two or more elements react with one another.

Unique Set of Properties

•Boiling Point

•Melting Point

•Density

•Color

•Reactivity with acid

•Reacts when exposed to light

Breaking Down a Compound

•Heat

•Electric Current

•Chemical Reaction

•COMPOUNDS CANNOT BE BROKEN DOWN BY PHYSICAL CHANGE.

Common Compounds•In NATURE

•Carbon Dioxide

•Sugar

•Proteins

•Water

•Sea Shells- Calcium

•Quartz

In Industry- Ammonia-Medicines-Food Preservatives-Synthetic Fibers

Mixtures

•Mixtures are combinations of substanes that are not bonded together and can be separated by physical processes.

Mixtures

•Unlike compounds, mixtures do not always contain the same proportions of the substances that they are composed of. Example: Lemonade

Mixtures

•A heterogenous mixture is a type of mixture where the substances are not mixed evenly.

•Example: Seeds in a watermelon

Mixtures

•A homogenous mixture contains two or more substances that are evenly mixed on a molecular level but still are not bonded together.

•Kool-aid

Mixtures

•Another name for a homegenous mixture is a solution.

How does a solid solution form?

•The substance that dissolves-or seems to disappear- is called the solute.

•The substance that does the dissolving (or there is more of it) is called the solvent.

Precipitate

•A precipitate is the solid that forms as a result of a chemical change.

•Soap Scum

Liquid Solutions

•In liquid, the solvent is a liquid.

•Carbonated drinks are liquid-gas solutions. Carbon Dioxide is the gaseous solute and water is the solvent.

•In liquid-liquid solutions, both solvent and solute are liquids.

Gaseous Solutions

•In gaseous solutions, a smaller amout of one gas is dissolved in a larger amount of another gas.

•The air you breathe is a gaseous solutions.

Solid Solutions

•In solid solutions, the solvent is a solid. The solute can be a solid, liquid, or gas.

•Brass and Steel are common solid solutions.

Solubility

•Water is the universal solvent.

•A solution in which water is the solvent is called an aqueous solution.