Nomenclature Chapter 9 24-September Suggested HW 9.1, 9.5, 9.7, 9.11, 9.15, 9.17, 9.25, 9.29, 9.35, 9.39, 9.43, 9.51, 9.55, 9.57, 9.67, 9.69, 9.71, 9.73, 9.75, 9.79, 9.89, 9.95, 9.99, 9.101, 9.105, 9.109, 9.113, 9.115, 9.117, 9.119, 9.123, 9.127, 9.137, 9.139a Lecture 6 1

Law of Definite Proportions 2 Compounds 1.Combinations of two or more elements connected through ionic or covalent bonds 2.Cannot be broken down by physical means, but the atoms can be separated by chemical processes 3.Definite and constant elemental composition Law of Definite Proportions In a pure compound, the elements are ALWAYS present in the same definite proportion by mass 2g blue 4g red How much Blue if we have a sample that is 8 g red? Mass of blue in compound Total mass of compound Mass Percent =

Law of Definite Proportions 3

4 Mass of Cu (g)Mass of Se (g) Mass of CuSe (g) Mass of Cu left over (g) Mass of Se left over (g) Product Ratio Cu:CuSe Product Ratio Se:CuSE

Formula Mass 5 Sum of atomic masses of all atoms present in one formula unit of a substance, expressed in atomic mass units Calculate the formula mass of: CH 4 NH 4 + NH 4 (OH) Riboflavin  C 17 H 20 N 4 O 6 cobalt 27 Co

The mole and Avogadro's Number 6 The mass of 1 atom is WAY too small to be useful on a regular basis Avogadro’s Number (N A ) 1 mol = x units How many atoms are present in 0.05 moles of CH 4 ? How many moles is 1 x 10 6 atoms of CH 4

The mole and Formula Mass 7 So why is this useful to chemists? Argon 18 Ar Formula mass = g mol -1 The mass of 1 Argon atom is amu 1 mole of Argon atoms = g Conversion factor! How many moles of Ar are present in 25 g? How many Ar atoms are present in 25 g?

Molar Mass 8 For a given molecule, the molar mass is the sum of atoms involved Molar Mass = Formula Mass CH 4 NH 4 + NH 4 (OH)Riboflavin  C 17 H 20 N 4 O 6

The Mole and Chemical Formulas 9 COCOCO2CO2 CO 3 2- Na 2 CO 3 How many moles of Oxygen in 1 mole of:

Summary of Mole Calculations 10 Number of molecules Moles of the molecule Avogadro’s Number Moles of Atoms In a Compound Molar Mass Mass of the molecule Molar Mass Mass of the atom Mass Percent Formula Subscript Number of atoms Formula Subscript Avogadro’s Number

Some Sample Problems 11 You measure 10 g of sodium in a sample of Na 2 CO 3. How many moles of oxygen are present?

Sample Problems 12 What is the mass of Silicon (in grams) in: x atoms of Si 1764 molecules of SiH 4

Sample Purity 13 If a 63 g sample of K 2 SO 4 is 72% pure: How much of the sample is not K 2 SO 4 ? How many moles of oxygen are present in the pure K 2 SO 4 ? For every 100 g of a sample, only 72 g is K 2 SO 4

Empirical Formulas 14 Chemical formulas that gives lowest whole number ratio of atoms Molecular FormulaEmpirical Formula C 2 H 6 C 2 H 6 O C 2 H 6 O 4 C 10 H 30 O 16 C 10 H 30 O 17 C 1.67 H 2 C 0.5 H 1 O 0.5 C 0.25 Cl 1 C 2.33 H 1.67 O

Determining Empirical Formulas 15 Freon is 9.933% carbon 58.63% chlorine 31.44% fluorine What is the Empirical Formula of Freon? 1.Assume 100g of freon 2.Determine the moles of each element 3.Divide all by the lowest number of moles 4.Multiply each number by an integer to get all to whole numbers

Determining Empirical Formulas 16 A compound is 26.85% potassium 35.35% chromium 38.06% oxygen What is the Empirical Formula

Determining Molecular Formulas 17 You determined the empirical formula of a compound to be C 2 HCl. This compound has a molecular formula amu. What is the molecular formula? You determined the empirical of a compound to be SNCl 2. This compound has a molecular formula amu. What is the molecular formula?

Empirical and Molecular Formulas 18 Empirical Formula Molecular Formula Molar Mass Mass Percentages or Actual Masses Moles of each Element Whole Number Ratio Combustion Analysis

Combustion Reactions 19 Combustion reactions occur when compounds react with O 2 to produce CO 2 and H 2 O (and sometimes another biproduct) CH 4 + O 2  CO 2 + H 2 O If g of methane is combusted, how much CO 2 is produced? How much H 2 O is produced?

Combustion Reactions 20 If a combustion reaction produces g of CO2 and g of H2O, what is the empirical formula of the hydrocarbon? C x H y + O 2  CO 2 + H 2 O