Chapter 10 Final Review

Chapter 10: Chem Review

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The Mole

The Mole can refer to # of atoms, # of molecules, OR # of particles.   1 mole = 6.02x10^23  Ex) 2 mol of Na is 1.204x10^24 Molar Mass: the # of grams in 1 mol of a material Ex) 1 mol of C is 12.01 grams

Percent Composition

Definition: % of Mass of each element in a compound Steps: 1: find the molar mass of each compound 2: Add those all up 3: Divide the mass of each element by the total mass 4: Multiply by 100  

Mass %

Definition: % of polyatomic ion or only one part of the compound Steps:  1: Follow the same steps as % composition 2: Add percentages of whatever part of the compound you need  

Backward

Definition: using % composition to find the mass of an element present in a sample Steps: 1: Change % to decimal  2: Multiply by mass of sample

Practice Problems

Percent Composition:  Find the % composition of NaNO3 Mass %: FInd the mass % of CO3 in MgCO3 Backward: If CaCl2 is 64% Cl, how many grams of Cl are in a 270 gram sample of CaCl2?

Empirical Formula

Def: compound formula with subscripts in lowest WHOLE NUMBERS From % Composition Steps: 1: Make % the # of grams ad convert to moles 2:  Divide through the smallest mole value.  Answers are subscripts 3: Put elements together and use subscripts (If 1 or more subscripts are 1/2 double ALL subscripts)

Emperical Formula (Cont.)

From actual masses: 1: Subtract to find the mass of the other element 2: Convert grams to moles 3: Divide through smallest mole value 4: Put elements together and use subscripts

Molecular Formula

Def: A multiple of an empirical formula where subscripts are not in lowest whole numbers Steps 1: Find the empirical formula if not already given 2: Calculate the molar mass 3: Divide the mass of the larger compound by empirical formula mass 4: Multiply empirical formula by your step three answer

Practice Problems

Empirical formula:  A compound was analyzed and found to contain 32.4% Sodium, 22.65% Sulfur, and 45% Oxygen.  What was the empirical formula? A 170 g sample contains 29.84 g Sodium, 67.49 g Chromium, and Oxygen.  What was the empirical formula? Molecular Formula: A compound with an empirical formula P205 has a molar mass of 284 grams/mol.  Find the molecular formula

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