chapter03 - 3.1 Molecular and Formula Masses Molecular mass...

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1 3.1 Molecular and Formula Masses • Molecular mass - (molecular weight) – The mass in amu’s of the individual molecule – Multiply the atomic mass for each element in a molecule by the number of atoms of that element and then total the masses • Formula mass (formula weight)- – The mass in amu’s of an ionic compound 2 Calculating Molar Mass • Calculate the molar mass for carbon dioxide, CO 2 • Write down each element; multiply by atomic mass – C = 1 x 12.01 = 12.01 amu – O = 2 x 16.00 = 32.00 amu Total : 12.01 + 32.00 = 44.01 amu 3 Your Turn! • Calculate the molar mass for each of the following: – Sulfur trioxide – Barium phosphate – Silver nitrate – Acetic acid 4 3.2 Percent Composition of Compounds • Calculate by dividing the total mass of each element in a compound by the molecular mass of the compound and multiplying by 100 • % composition allows verification of purity of a sample
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5 % Composition 6 % Composition • Calculate the percent composition of iron in a sample of iron (III) oxide • Formula: Fe 2 O 3 • Calculate formula mass – Fe = 2 x 55.85 = 111.70 amu – O = 3 x 16.00 = 48.00 amu Total mass : 111.70 + 48.00 = 159.70 amu 7 % Composition % by mass = 111.70 159.70 × 100 = 69.9% Fe What is the % oxygen in this sample? (hint :100%) Hint: you can subtract the percent iron from 100% 8 Your Turn! • Calculate the percent oxygen in a sample of potassium chlorate
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9 3.3 Chemical Equations • Chemical equations represent chemical “sentences” • Read the following equation as a sentence – NH 3 + HCl NH 4 Cl – “ammonia reacts with hydrochloric acid to produce ammonium chloride” 10 Chemical Equations Reactant : any species to the left of the arrow (consumed) Product : any species to the right of the arrow (formed) State symbols : – ( s ) solid ( l ) liquid ( g ) gas – ( aq ) water solution 11 Balancing Equations Balanced : same number and kind of atoms on each side of the equation 12 Balancing Equations Steps for successful balancing 1. Change coefficients for compounds before changing coefficients for elements.(never change subscripts!) 2. Treat polyatomic ions as units rather than individual elements. 3. Count carefully, being sure to recount after each coefficient change.
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13 Balancing Equations • Balance the equation representing the combustion of hexane __ C 6 H 14( l ) + __ O 2( g ) __ CO 2( g ) + __ H 2 O ( l ) (hint: make a list of all elements and count to keep track) 14 Balancing Equations • Balance the equation representing the combustion of hexane C 6 H 14( l ) + 19/2 O 2( g ) 6 CO 2( g ) + 7 H 2 O ( l ) So…multiply through the entire equation to eliminate fractions 2 C 6 H 14( l ) + 19 O 2( g ) 12 CO 2( g ) + 14 H 2 O ( l ) 15 Chemical Equations • Equations can represent physical changes KClO 3( s ) KClO 3( l ) Or chemical changes • Note the symbol for heat above the arrow 2 KClO 3( s ) 2 KCl ( s ) + 3 O 2( g ) Δ  → 16
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This note was uploaded on 03/03/2010 for the course CHEM CHEM400 taught by Professor Stewart during the Spring '10 term at American River.

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chapter03 - 3.1 Molecular and Formula Masses Molecular mass...

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