Stoichiometry Presentation Chapter 3 Notes

3.5 Determining the Formula of a Compound 1. Determine the % composition of each of the elements 2. Treat the % as grams and convert from grams to moles for each element in the compound 3. Find the smallest whole number ratio of moles 4. If the ratio is not a whole number, find an integer to multiply the whole equation by to get the lowest WHOLE number ratio. Usually 2, or 3.

Determining the Molecular Formula Find the empirical formula mass of the compound Divide the known molecular mass by the empirical formula mass to determine a whole number Multiply the empirical formula by the whole number integer to get the correct molecular formula

3.8 Stoichiometric Calculations 1. Balance the chemical equation to get the correct stoichiometric ratio for all reactants and products 2. Convert grams of reactant or product into mole amounts 3. Use the stoichiometric ratio along with the calculated mole amounts to solve for moles or grams of desired substance 4. Check and ask yourself if the answer makes sense based on give values

3.9 How to solve a problem with a limiting reagent 1. Balance the equation to obtain stoichiometric ratios 2. Convert grams of reactants to moles of reactants 3. Use the stoichiometric ratios along with the moles of reactants to determine how much product can be obtained using each reactant 4. The reactant that produces the least amount of product based on given ratios is the LIMITING REAGENT 5. Once LR is known, we can determine maximum amount of product formed

Calculating Percent Yield 1. Actual Yield is what you make during an experiment 2. Theoretical Yield is what you should have made based on given masses and stoichiometry No process is 100% efficient, so we always make less than we predict To calculate divide actual yield by theoretical yield and multiply by 100 to convert to a %.

3.10 Combustion Analysis Process where a sample is burned (Usually a hydrocarbon) in a large excess sample of oxygen gas Each product is isolated and the weight of each combustion product is determined Used to calculate the efficiency of a combustion based procedure

How to Calculate 1. All elements will be given to you and typically are C, H, O, and N 2. Moles of C will come from amount of CO2 in liters (22.4L = 1 mol) 3. Moles of H will come from amount of H2O in grams 4. Oxygen can be figured out once we know the amount of C, and H, and Nitrogen is usually given to us if its part of the compound 5. Once all mole amounts are known this becomes an empirical formula problem