Dimensional Analysis

STOICHIOMETRYUNIT 2Video 2.1Moles and Molar MassStoichiometryThe Mole represents a specific amount of any substance.Specifically it represents 6.02x1023 particles such as atoms and molecules.

The Mole = 6.02x1023The mole is based on the fact that 12 grams of Carbon-12 has a mole of atoms. A mole means you have 6.02x1023 particles.

Molar MassMolar Mass (aka gram formula mass or molecular mass) is the mass of one mole of a substance. Elements molar masses are reported on the periodic table.

Molar Mass Examples: ElementsWhat is the molar mass of iron?

What is the molar mass of copper?

55.8 g/mol63.5 g/molMolar Mass Examples: CompoundsWhat is the molar mass of water?

H2O = 2(1.0) + 16.0 = 18.0g/mol

What is the gram-formula-mass of calcium chloride? CaCl2 = 40.1 + 2(35.5) = 111.1 g/mol

Video 2.2Calculating MolesWhat if you have more than one mole of a substance?Use the formula on table T:

number of moles = given mass (g) _ gram-formula mass

(Given mass will be your answer.)Lets try these togetherCalculate the mass of 6.70 moles of carbon.

Calculate the mass of 0.023moles of lithium.

Calculate the mass of 25.02 moles of calcium phosphate.The gfm formulaUse the same formula to calculate the moles, placing the number in the question on the numerator:number of moles = given mass (g) gram-formula massLets try these together4. Determine the number of moles in 8.0 grams of Boron.

Determine the number of moles in 0.567 grams of Helium.

Find the number of moles in 1230 grams of magnesium sulfate.

Video 2.3Moles to CoefficientsCoefficients4Al + 3O2 2Al2O3 reactants products

Coefficients: How many moles of the substance are needed in a reaction.Relating MolesTo relate moles of one substance to another, simply create a proportion:

4Al + 3O2 2Al2O3

If 3 moles of oxygen react, how many moles of Aluminum oxide form?If 4 moles of aluminum react, how many moles of oxygen are needed?If 4 moles of aluminum oxide are formed, how many moles of oxygen were used?If 8 moles of aluminum react, how many moles of oxygen are needed?Relating Moles16 Al + 3S8 8Al2S3

If 2.50 moles of sulfur react, how many moles of aluminum sulfide form?

If 3.75 moles of aluminum react, how many moles of sulfur are needed?THINKWhy do chemists use moles to measure substances? Why arent grams, liters and molecules enough?

Video 2.4BalancingConservation of MassIn a reaction, atoms and molecules cannot appear or disappear. Mass must stay constant from the beginning to the end of the reaction.H2 + O2 H2O___H2 + ___O2 ___ H2OBalancing Reactions___ N2 + ____H2 ____ NH3

___Li + ____O2 ___Li2OBalancing __Pb(NO3)2 +__K2CrO4___PbCr2O4 + ___KNO3

___C4H8 + ___O2 ___CO2 + ___H2OTypes of ReactionsSynthesis: A + 2B AB2Decomposition: AB2 A + 2BCombustion: CH4 + O2 CO2 + H2OSingle Replacement:AB + C CB +ADouble Replacement:AB + CD AD + CB

* Notice synthesis and decomposition are opposites. Also, combustion can have any carbon compound as a reactant.Video 2.5Empirical and Molecular FormulasEmpirical FormulasDetermine the mass of each element in water.What is the ratio of mass of hydrogen to mass of oxygen in water?Is the ratio of mass related to the formula of water?Find the moles of H and O in water.Is the ratio of moles related to the formula of water?

Empirical FormulasEmpirical formula refers to any molecular formula in its reduced form.

Are these empirical? If not, reduce them:C2H2C6H12O6NO2Na2(OH)2

CHCH2ONO2NaOHMolecular FormulasMolecular Formulas are some multiple of the empirical formula.Example: If the empirical formula is CH4 a molecular formula could be CH4, C2H8, C3H12 etc.

A compound whose empirical formula is NH3 has a mass of 34 g/mol. What is the empirical formula?Steps:Find the mass of the empirical formula.Divide the mass given by the empirical mass.Distribute your answer through the empirical formula.

If a compound has a mass of 45 g/mol and an empirical formula of CH3, what is the molecular formula?Video 2.6Percent CompositionPercent CompositionNutrition Facts on foods can tell you just how much of a substance you are consuming and how that relates to how much you should eat in a day.It is equally important to know how much of a element or compound is in a mixture.

Percent CompositionBy mass: mass part x 100 total mass

Find the % by mass of phosphoric acid.

Find the percent by mass of Ca in Ca(OH)2.Find the percent by mass of Na:NaClONaClNaOH23.0/74.5 *100 = 30.9%23.0/58.5 *100 = 39.3.%23.0/40.0 *100 = 57.5%Percent Composition Examples1. A sample of a substance containing only magnesium and chlorine was tested in the laboratory and found to be composed of 74.5% chlorine by mass. If the total mass of the sample was 190.2 grams, what is the mass of the magnesium?