Problem Solving Sample Problem Note: Always balance the equation: FezO3 (s) + 2 Al (s) - 2Fe (1) + AlzO3 (s) 1. How many grams of Al (MM=27 g/mol) will react with 80g of FezOz (159.7g/mol) ? 2. How many grams of a) Fe (MM = 55.86g/mol) and b) AlzO (MM = 102g/mol) is produced from 80g of Fe203 with 45g of Al? use FezO; Solution: Find the molecular mass of your compound/ element. 1. m of Al = 2 mol AL 27g Al 80g Fez03 X 1mol Fe203 159.7g Fez 03 1mol Fe203 1mol Al = 27.05g Al 2. a) m of Fe = 1mol Fe203 2 mol Fe 55.86g Fe 80g Fe203 X = 55.969 Fe 159.7g Fe203 1mol Fe203 1mol ke b) m of Al203= 80g Fez03 X - 1mol Fez0s 1 mol Al203 X 1029 Al203 = 51.10 Al203 159.79 Fe203 1 mol Fe203 imol Al203 Practice Problem NaOH (aq) + H2SO4 (aq) - H20 + NazSOA a) How many grams of H2SO, will react with 120g NaOH b) How many grams of H2O and NazSO4 is produced by 1 15g of NaOH with 100g H2SOA? Use NaOHSteps in balancing chemical equations 1. Write the chemical equation. Example combustion reaction of propane (CsHs) that produces water (H2O) and carbon dioxide (CO2) CHs (9) +Oz (9) -> H2O (9) + CO2 (g) 2. Write down the number of atoms per element 3 C 8 H N 2 O 3 3. Trial and error make sure that each side will have the same number of atoms. Ex. To balance carbon the product side containing carbon should also be 3. Add a coefficient 3 to the compound that contains carbon. CaHa (g) +02 (g) - H20 (g) + 3 CO2(g) 3 C 8 H 2 2 O 3-7 Since three was added to carbon dioxide, the number of oxygen atoms will also change. 4. Do the same thing to all other elements CaHs (g) +5 02 (g) -> 4 H20 (g) + 3 CO2(g) 3 C 1 3 8 H 2 8 10 2 O 3 7 10 Problem Solving A. Write the state of matter each element or compound and the equation, if needed. Then balance the equation. 1. CaCh + NasPO. yield Ca3(PO4)2 + NaCI 2. Mg + HCI yield MgCk2 + H2 3. C.H&N2 + NO. yield N2 + CO, + water 26Problem Solving Sample Problem Using the stoichiometry sample problem 2.a. Find the percent yield of iron (Fe) if the reaction was able to produce 45.82g Actual Yield(g) Formula: Percent Yield =; Theoretical Yield (g) x 100 Percent Yield of Fe = 45.82g x 100 55.969 Percent Yield of Fe = 81.88% Practice Problem Use your answer in practice problem for stoichiometry. Find the percent yield of NazSO, if the actual yield is 62.42g. Is the reaction successful or not