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# %Composition

## by ZB Chemistry on Feb 10, 2011

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## %CompositionPresentation Transcript

• % composition
• Moles & Formulas
• A chemical formula really tells us how many moles of each element make one mol of the compound.
• Examples:
• H 2 O means 1 mol of water is made of 2 moles of H and 1 mol O.
• Na 2 SO 4 = 2 mol Na, 1 mol S, 4 mol O
• Now that we have studied the mole we can use this information to find % composition.
• % Composition
• A ratio
• Helps to identify a substance.
• Compares masses of elements in a compound.
• How to Calculate % Composition
• Write the formula (if it isn’t given).
• Find the molar mass of the compound.
• Divide the molar mass of each element by the molar mass of the compound.
• Multiply by 100. (this gives a %)
• Check your work! If you did it right all the percents will add up to 100.
• Example: Find the % composition of Potassium Chlorate.
• KClO 3
• K = 1 x 39.10 = 39.10
• Cl = 1 x 35.45 = 35.45
• O = 3 x 16.00 = 48.00
• 122.55g/mol
• (39.10/122.55) x 100 = 31.91% K
• (35.45/122.55) x 100 = 28.93% Cl
• (48.00/122.55) x 100 = 39.17% O
• 31.91 + 28.93 + 39.17 = 100.01… remember we rounded
• Example: Find the % composition of Ammonium Phosphate.
• (NH 4 ) 3 PO 4
• N = 3 x 14.01 = 42.03
• H = 12 x 1.01 = 12.12
• P = 1 x 30.97 = 30.97
• O = 4 x 16.00 = 64.00
• 149.12g/mol
• (42.03 /149.12) x 100 = 28.19% N
• (12.12 /149.12) x 100 = 8.13% H
• (30.97 /149.12) x 100 = 20.77% P
• (64.00/149.12) x 100 = 42.92% O
• 28.19 + 8.13 + 20.77 + 42.92 = 100.01… remember we rounded
• Homework
• Page 248
• “ practice” at the top of the page do #s 1,2,3,4abcd,5a
• Page 248 Section Review #6abcd