Pure Substances Vs Mixtures

Classification of Matter: Pure Substance or Mixture?

Pure Substances • Substances which have unique, identifying properties are called pure substances. • There are two types of pure substances: – Elements – Compounds

Element • This is a platinum Gundam stature worth $250,000. • Platinum (Pt) is an element.

Compound • This is the structure of ascorbic acid (vitamin C) • Foods high in vitamin C include green peppers, broccoli, cabbage, lemons, oranges, grapefruit, tomatoes and potatoes.

What is the difference between an element and a compound? • An element is a pure substance which is composed of only one type of atom. All of the elements are listed on the periodic table. • A compound is a pure substance which is composed of more than one type of element.

What are some examples of elements and compounds? • Some examples of elements include oxygen (O), carbon (C), iron (Fe), gold (Au), and fluorine (F). • Some examples of compounds include water (H2O), sugar (C12H22O11), rust (Fe2O3), and salt (NaCl).

Carbon - an element

Copper Sulfate - a compound

More About Compounds • The properties of compounds are different from the properties of the elements which compose them. • Compounds can be decomposed into elements only by chemical reactions, they can not be physically separated.

Chlorine

Example • Sodium is an element that is a silvery gray metal and is also neutral. • Chlorine is an element is a neutral greenish-yellow, poisonous, diatomic gas (Cl2).

More About Compounds • Compounds have a definite chemical composition identified with a chemical formula. • For example, the ratio of the number of oxygen atoms to hydrogen atoms in any sample of water is always 1 to 2.

Mixtures • When two or more component substances which retain their own identifying properties, the matter is classified as a mixture. • Mixtures do not have a definite composition. The components of a mixture may be in any ratio. – You can have sweet tea that has a lot of sugar or sweet tea with less sugar.

More About Mixtures • A mixture can be separated physically because the components of the mixtures have different physical properties. • Procedures for separating mixtures include: dissolving, filtering, evaporating, decanting, magnetic separation, separating by particle size, or chromatography.

Decanting

What are the two groups that mixtures can be classified into? • Mixtures can be heterogeneous or homogeneous. • Heterogeneous mixtures do not have the components distributed evenly throughout. The different components are easy to see in a heterogeneous mixture.

Homogeneous Mixtures • Homogeneous mixtures have components distributed evenly throughout. • Solutions are homogeneous mixtures in which the components are close to the size of individual particles of the substance (atoms, molecules, or ions)

Homogeneous or Heterogeneous?

Mixtures can occur between and among all phases of matter. • Mixtures can be: – Gas/gas (air) – Gas/liquid (oxygen in water) – Liquid/liquid (alcohol in water) – Liquid/solid (sugar in water) – Solid/solid (alloy such as steel)

Steel

Molecules and Compounds

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Mixtures

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