CHEMICAL COMPOUNDS AND THE MOLE Chapter 7

Formula Mass  Mass of H 2 O?  Formula Mass: mass of molecule, formula unit, or ion is sum of masses of all atoms represented (amu)  Ca(NO 3 ) 2

Molar Mass  Definition: mass of 1 mole of compound – use molar masses of elements (g/mol)  MgCl 2  (NH 4 ) 2 CrO 4  CuSO 4 * 5H 2 O

Molar Mass in Conversions  Remember flow chart from chapter 3?  What is mass (g) of 3.04 mol of ammonia vapor, NH 3 ?  How many moles of sodium chloride are present in grams?

PRACTICE MOLAR MASS Work as a group of 4.  1 st group member: 1,5,9,13,17,21 GroupII:1  2 nd group member: 2,6,10,14,18,22 Group II:2  3 rd group member: 3,7,11,15,19,23 Group II:3  4 th group member:4,8,12,16,20,24 Group II:4 Show work for each problem you complete. Explain your work to the other group members and write in their answers. HW: complete your set and

“Super Mole” Conversions  How many molecules are in 4.15 x g C 6 H 12 O 6 ?  How many H atoms are in 7.1 moles of C 6 H 12 O 6 ?  How many formula units are in 4.5 kg Ca(OH) 2 ?

More “Super Mole” Conversions  What is the mass of H 2 SO 4, if you have 1.53 x sulfate ions your compound?  How many water molecules are present in in a 5.00 g sample of copper (II) sulfate pentahydrate?

Percent Composition  The percent by mass of each element in a compound.  % = mass due to 1 element x 100 mass of whole compound

Percent Composition  What is the percent composition by mass of each element in (NH 4 ) 2 O?  What percentage by mass of Al 2 (SO 4 ) 3  6H 2 O is water?  Given a 25.0 gram sample of aluminum sulfate hexahydrate, how much water (g) could be driven off?

Empirical Formula  Definition: formula showing smallest whole-number mole ratio of atoms in a compound  Ex: B 2 H 6  Molecular Formula BH 3  Empirical Formula  Given (CH2O)x as the empirical, determine possible molecular formulas.

Empirical Formula Calculation  Given the molecular formula: reduce  Given % compostion data  Find grams of each element  Find moles of each element  Find mole ratio of atoms by dividing through by the smallest number of moles  If the ratio yields a 0.33, 0.50 multiply the entire formula through to clear fractional mole amounts.

Finding Empirical Formula  Determine the empirical formula of the compound with 17.15% C, 1.44% H, and 81.41% F.  (CHF 3 )x

Finding Empirical Formula  Find empirical formula of 26.56% K, 35.41% Cr, and rest O.  (K 2 Cr 2 O 7 )x

Finding Molecular Formula x(empirical formula) = molecular formula x(emp.form mass) = molec.form mass x = Molecular formula Mass Empirical formula Mass

Finding Molecular Formula  Determine molecular formula of compound with empirical formula CH and formula mass of amu.

Finding Molecular Formula  Sample has formula mass of amu has 0.44 g H and 6.92 g O. Find its molecular formula.

Combustion Analysis  A compound contains only carbon, hydrogen, and oxygen. Combustion of the compound yields grams of carbon dioxide and grams of water. The molar mass of the compound is g/ mol. The sample has a total mass of.0100 grams. What are the empirical and molecular formulas of the compound?