Chapter 9 Key Terms Mole Molar Mass Avogadro's Number Percent Composition Stoichiometry Limiting Reactant Excess Reactant Actual Yield Theoretical Yield Structural Formula Molecular Formula Empirical Formula Percent Yield Law of Definite Composition 1

Chemical Calculations Chapter 9 Chemical Calculations

The Mole Used to measure many small items quickly Defined: the amount of substance contained in 6.022 x 1023 units When used in equations, we will use 4 significant figures for the mole Perspective: If you had 1 mole of dollars, how long would it take you to spend all of your money if you spent it at a rate of $1 million per second?

The Mole $6.022 x 1023 1 sec 1 hr 1 day 1 year $1 x 106 3600 s 24 hrs 365 days Over 27 billion years

Molar Mass Describes the mass of 1 mole of any pure substance The mass of 1 mole of any element is shown on the periodic table 1 C atom weighs 12.011 amu’s 1 mole of C atoms weighs 12.011 g

Molar Mass What is the mass of 1 mole of carbon? 12.011 grams How many atoms in 1 mole? 6.022 x 1023 What is the mass of ½ mole of carbon 6.0055 grams 12.011 g of carbon contains the same number of atoms as 1 mole of carbon

Molar Mass What is the mass of 1 mole of gold? 196.96655 g How many atoms? 6.022 X 1023 What is the mass of ½ mole of gold? 98.483275 g 12.011 g of carbon contains the same number of atoms as 196.96655 g of gold

Molar Mass What is the mass of 1 mole of Mg? 24.3050 g What is the mass of 2 moles of Mg? 48.6100 g How many atoms in 2 moles? 1.204 x 1024 12.011 g of C contains the same number of atoms as 196.96655 g of Au and the same number of atoms as 24.3050 g of Mg

Molar Mass Molar mass: the mass of 1 mole of a pure substance in grams The substance can be a compound or an element Molar mass of water (H2O) 2 H = 2 mol x 1.00794 g/mol = 2.01588 g 1 O = 1 mol x 15.9994 g/mol = 15.9994 g 2.01588 g + 15.9994 g = 18.01528 g = molar mass of water

Molar Mass Calculate the molar masses of the following compounds: HCl Mg3(PO4)2 Mg(OH)2

Types of Formulas Structural formula Molecular Formula Shows the arrangement of atoms in the compound Molecular Formula Shows the types and numbers of atoms involved as they appear in the molecule Empirical formula Shows the elements present in the simplest whole-number ratio

Percent Composition Describes the mass composition of a compound by showing what percentage of its total mass comes from each element Percent composition = part/whole x 100% A 60.00 gram sample of water decomposes into 6.72 g H and 53.28 g O. What is the percent composition of water? H = 6.72 g / 60.00 g x 100% = 11.2% O = 53.28 g / 60.00 g x 100% = 88.80%

Percent Composition 30.00 g sample of Al2(SO4)3 contained 4.731 g Al, 8.433 g S, and 16.836 g O. What is the percent composition? 4.731 g Al / 30.00 g = 15.77 % Al 8.433 g S / 30.00 g = 28.11 % S 16.836 g O / 30.00 g = 56.12 % O

Calculations with Empirical Formulas 1 mole of H2O 2 H @ 1.00794 g/mol = 2.01588 g H 1 O @ 15.9994 g/mol = 15.9994 g O Total mass of 18.01528 g H2O Find percent composition H = 11.19% O = 88.81%

Percent Composition Calculations Caffeine is made up of 5.170% H, 16.49% O, 28.86% N, and 49.48% C by mass. What is the empirical formula for caffeine? C4H5N2O

Stoichiometry The relationships between the amounts of reactants and products in a chemical reaction Give mass of a substance and asked for mass of the other reactant for the reaction to fully occur Give mass of reactants and ask for mass of product Give mass of both reactants and asked which will run out first Limiting Reagent: reagent/reactant that runs out or limits the process from continuing Excess Reagent: reagent/reactant left over after reaction

Moles of substance Mass of substance Moles to Mass Molar mass of substance Moles of substance Mass of substance Calculate the number of moles in 26.00 g of NaOH 26.00 g NaOH 1 mole NaOH = 0.6500451 = 0.6500 mol NaOH 39.99704 g NaOH

Molar Mass Calculate the mass in g if 0.02 moles of NaOH are present Calculate how many moles of water are present in 10 g 0.02 mol NaOH 39.99704 g NaOH = 0.7999408 = 0.8 g NaOH 1 mole NaOH 10 g H2O 1 mole H2O = 0.55508 = 0.6 mol H2O 18.01528 g H2O

Moles to Number of Atoms Number of atoms or molecules Avogadro’s Number Moles of substance Calculate the number of Na atoms if you have 0.34 moles 0.34 mol Na 6.022 x 1023 atoms Na = 2.04748 x 1023 = 2.0 x 1023 atoms Na 1 mol Na

Number of atoms or molecules Stoichiometry Avogadro’s Number Molar mass of substance Number of atoms or molecules Moles of substance Mass of substance

Stoichiometry Now, we can find out how much of other substances are needed or produced using the chemical equation Mole ratios Shows the ratio between the moles of one substance and the moles of another substance in a chemical reaction 2 H2 + O2  2 H2O P4 + 5 O2  2 P2O5 If someone wanted to produce 25.0 moles of P2O5, how many moles of P4 are needed?

Moles of substance 1 Moles of substance 2 Coefficients Moles of substance 2

Stoichiometry Find the mole to mole ratio of the “ingredients” – shown by the coefficients 1 CH4 + 2 O2  1 CO2 + 2 H2O Convert based upon what you are given and what you need Mass to moles Moles to moles Moles to mass

Mass (grams) Mass (grams) Mole Mole Particles Particles Molar mass (periodic table) Molar mass (periodic table) Mass (grams) mole ratio Mole Mole Particles (atoms, molecules, formula units) Particles (atoms, molecules, formula units) 6.02 x 1023 6.02 x 1023

Problems What mass of water will react with 3550 grams of diphosphorus pentoxide? P2O5 + 3 H2O 2 H3PO4 Mole ratio = 1:3 Mass to mole, mole to mole, mole to mass

Problems How many grams of NaCl must be decomposed to yield 27 g of chlorine gas? First write out the balanced equation

Problems 2 Na + Cl2 2NaCl How many grams of sodium chloride are produced from 46 g of sodium and excess chlorine? How many moles of O2 are produced when 3.00 moles of Al2O3 decompose?

Problems If 56 g of Fe are added to a solution of copper (II) sulfate, how much solid copper will form? 2 Fe + CuSO4 Fe2(SO4)3 + 3 Cu How many moles of copper can be produced from 446 g Cu2SO4? Zn + Cu2SO4 ZnSO4 + 2 Cu