Pure Substances & Mixtures

What is a pure substance ?

Pure Substance  A substance in which there is only one type of particle.  The particles of a pure substance are alike no matter where they are found.  Ex: Particles of iron in a skillet are the same as the iron particles found in a meteorite

Element  Is a pure substance that cannot be separated into simpler substances by physical or chemical means.  It only has one type of atom.

Compounds  A pure substance composed of two or more elements that are chemically combined.  Salt- Sodium & Chlorine  Water- hydrogen & oxygen  Sugar- carbon, hydrogen & oxygen  Baking soda- sodium, hydrogen, carbon, and oxygen.

Compounds aren't Random  The elements that make up a compound join in a specific ratio according to their masses.  Water  2 atoms of hydrogen to 1 atom of oxygen (2:1 ratio)  1g hydrogen to 8g oxygen = 1:8 = 1/8  Each compound has its own set or identifying properties different from the elements that it is formed from.

What is a mixture ?

Mixture  Is a combination of two or more substance that are not chemically combined.  The substance in a mixture retain their identity.  Ex: pizza, salt water

Solutions  Are mixtures that appear to be a single substance.  They are still composed of two or more substance but they are distributed evenly amongst each other

Parts of a Solution  Solute- The substance that is dissolved  Ex: salt  Solvent- The substance in which the solute is dissolved in.  Ex: Water  Salt is soluble in water  When two liquids or gasses for a solution the substance of greater volume is the solvent.

 Aqueous Solution – a solution in which water is the solvent.  Electrolyte – a solution that conducts electricity.  Nonelectrolyte – a solution that does not conduct electricity.

 Saturated solution – when the solvent can not hold anymore solute. Three factors that speed up dissolving: - temperature - stirring - particle size - particle size

More on Mixtures:  Concentration: measures the amount of a solute dissolved in a solvent.  Solutions can be described as being concentrated or diluted.  Solubility: The amount of solute needed to make a saturated solution ( grams/ 100mL)  Saturated: A solution that contains all the solute is can hold at a given temperature.  Unsaturated: A solution that contains less solute then it can hold at a given temperature.

Types of Mixtures:  Suspensions: A mixture in which particles or a material are dispersed throughout a liquid or gas but are large enough that they settle out.  Colloids: A mixture in which particles are dispersed throughout but are not heavy enough to settle out. Ex: Milk, Jell-O, Fog They cannot be separated by filtration the particles are too small

Mixtures Vs. Compounds MixturesCompounds Components are elements, compounds, or both. Components are elements. Components keep their original properties. Components lose their original properties. Separated by physical means.Separated by chemical means. Formed using any ratio of components Formed using a set mass ratio of components.

Mixtures are Either:  Homogeneous: Have the same appearance and properties throughout the mixture  Ex: Solutions- milk, Kool-Aid  Heterogeneous : the different components are easily seen.  Ex: suspensions- salad dressing, muddy water.

Yet Another Way To Classify Matter

How do you separate a mixture?  By:  Physical separation (take topping off pizza)  Distillation (based on boiling points)  A magnet (certain metals)  A centrifuge (separates by density)  Filter (solid particles)  Evaporation (sodium chloride & water)