Chemistry 1441 1st Edition Exam 2 Study Guide Chapters 3 4 Chapter 3 Stoichiometry of Formulas and Equations Mole and Molar Mass 1 Mole is a number word 6 022x1023 is called Avagadros Number Na mole is often abbreviated as mol These and equalities conversion factors for dimensional analysis Ex How many moles of atoms are present in 9 5x1015 atoms 1 mol atoms mol atoms 9 5x1015 atoms x 1 6x10 8mol atoms 6 022 10 23 atoms 2 Mole relates to mass Molar mass uses to convert moles to mass and mass back to moles Ex 1 mol C 12 01g C Ex 1 mol H2O 2 x 1 008 x 1 x 16 00 18 02g H2O Molar mass formula M mass n M Molar mass N number of moles Ex How many iron atoms are in 675g of iron 23 1 molFe 6 022 10 Fe atoms Fe atoms 675 g Fe 7 28 1024 Fe atoms 55 85 gFe 1 molFe Hint A simple way to work these problems out is to write down what you want to find and equal it to what you have and then go from there 3 Mol to Mol ratios can be found From the subscripts of chemical formulas magnesium nitrate Mg NO3 2 Coefficient of Balanced Formulas THAT S WHY KNOWING HOW TO BALANCE EQUATIONS IS VITAL BECAUSE YOU NEED TO KNOW THE CORRECT COEFFICIENT TO SOLVE PROBLEMS such as when we get to COMBUSTION REACTIONS Mole to Mole Ratios from Chemical Formulas Ex How many ions are in 15 0 g of aluminum carbonate NH 4 2 CO 3 NH 4 2 CO 3 NH 4 2 CO 3 1 mol 96 09 g 1 mol NH 4 2 CO3 ions 15 0 g Balancing Chemical Equations Ex 1 Fe3O4 4 H2 3 Fe 4 H2O Combustion Reactions When a hydrocarbon compound containing only C and H or a compouns containing only C H and O goes through a complete combustion in oxygen the products are CO2 and H2O Ex C Hor C H O O2 CO2 H2O Reaction Stoichiometry For stoichiometry problems we must balance the equation correctly and use the coefficients to determine the quantities in chemical reactions Ex complete combustion reaction What mass of oxygen gas is required for the complete combustion of 10 0 g of cyclopentanol C5H9OH 1 C5H9OH 7 O2 5 CO2 5 H2O 1 mol C 5 H 9 OH 7 mol O2 32 00 g O2 g O2 10 0 g C 5 H 9 OH 26 0 g O2 86 13 g C5 H 9 OH 1 mol C5 H 9 OH 1mol O2 Percent Yield Percent Yield actual yield 100 theoretical yield Limiting Reactant The limiting reactant is the reactant you run out of first Ex If you have 20 men and 30 women and you are pairing up couples with the 1 1 ration then you would run out of men and have 10 women left without partners The men would then be the limiting reagent and the women would be the excess reagent because you have an excess of 10 women Percent Composition of Compounds part whole x 100 Ex What is the percent of hydrogen in water H mass H mass H2O x 100 H 2 x 1 008 18 02 x 100 H 11 2 Empirical and Molecular Formulas Molecular formula the of atoms in each element in a molecule Empirical formula the smallest whole number mol to mol ratio of elements Ex The molecular formula of benzene is C6H6 The Empirical formula would be CH 6 6 is equivalent to 1 1 ratio Chapter 4 Three Major Classes of Chemical Reactions Molarity and Solution Stoichiometry Molarity M mol solute Vsolution L OR M n V Solution by dilution M1V1 M2V2 OR MconcVconcentration MdilVdilution Electrolytes 1 Review Names formulas charges of all ions Aqueous solutions solvents solutes solutions 2 Go back and review aqueous solutions and the conduction of electricity 3 When ionic compounds dissolve in water they dissociate into ions 4 Review what ionization means 5 Know what electrolyte means 6 Strong Electrolyte 7 Weak electrolytes 8 Nonelectrolytes 9 Strong Acids 10 Strong Bases 11 Define salts Precipitation Reactions Occurs when 2 soluble ionic compounds form an insoluble product Known as double replacement reqaction MUST KNOW SOLUBILITY RULES review notes Soluble Ionic Compounds Insoluble Ionic Compounds EX Cu OH 2 Insoluble Strong electrolyte strong base Acid Base Reactions Double displacement OR Metathesis Reactions Two types Precipitation and Acid Base Reactions Solution Stoichiometry 1 Write out the balanced equation 2 Write what your given of each compound 3 Write what you are looking for and equal it to the volume you are given 4 When conduct a dimensional analysis until the unit you don t need are canceled and you have to unit you need REFER toNOTES for MEMORIZATION RULES and Chapter 1 2 material