Determining the concentration of a mixture - 20 points

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There are a number of ways to state the concentration of a mixture.  A percentage and a ratio.  These are NOT the same thing.

1.    As a percentage of the whole.                   

Usually mixtures are expressed as a percentage by weight or sometimes by volume.  Sometimes you need to determine this percentage when dissolving a substance in water.  Keep in mind that water has a mass of 1g/cm³.  Therefore, 1000mL of water has a mass of 1000 grams.  Knowing the mass of the dissolved substance allows you to compute the percentage by weight.

Express your percentage in the form of mass of substance/mass of total mixture.

Example:    You mix 5 pounds of broccoli and 3 pounds of cauliflower in your restaurant.  What is the percentage by weight of the broccoli?

Mass of broccoli/Mass of mixture = 3/8 = .375 or 38%

Example:     What is the percentage by weight of Oxygen in water?

Water is H₂O.  The atomic mass of water is (2H x 1 amu) + (1O x 16 amu) = 18 amu.

Mass of Oxygen/Mass of Water = 16/18 = .888 or 89%.

2.   In the form of a ratio.

Sometimes mixtures are expressed as a ratio.  The smaller number is placed first.

Example:    You mix 5 pounds of broccoli and 3 pounds of cauliflower in your restaurant.  What is the ratio by weight of the mixture?

Mass of cauliflower : Mass of broccoli = 3:5

Example:     What is the ratio by weight of Oxygen and Hydrogen in water?

Water is H₂O.  The atomic mass of water is (2H x 1 amu) + (1O x 16 amu) = 18 amu.

Mass of Hydrogen : Mass of Oxygen = 2:16