Chemical Relationships Stoichiometry: The proportional nature of chemical reactions by Robin Marks, M.A., Anthony Carpi, Ph.D. Reading Quiz Teach with this Given the equation for a s’more: 2 Graham crackers + 1 piece of chocolate + 4 mini-marshmallows --> 1 s’more Which of the following activities makes accurate use of stoichiometry to plan for 1 s’more per person at a bonfire with 20 guests? Purchasing at least twice as many pieces of chocolate as graham crackers . Buying 1 bag of mini-marshmallows and 2 boxes of graham crackers because there are more marshmallows per bag than there are graham crackers per box. Substituting marshmallow creme for the mini-marshmallows because that would produce a greater mass of s’mores overall. . Buying 40 graham crackers, 20 pieces of chocolate, and 80 mini-marshmallows Given the equation: Na3PO4 + 3 KOH --> 3 NaOH + K3PO4 What is the first step in determining how much sodium hydroxide (NaOH) is produced when starting with 5 grams of sodium phosphate and excess potassium hydroxide? Determine how many grams of potassium hydroxide will be used up in the reaction. Convert 5 grams of sodium phosphate to moles Determine the molecular weight of sodium hydroxide Use the mole ratio of potassium hydroxide and sodium hydroxide Given the equation: 2 Al + 6 HCl --> 3 H2 + 2 AlCl3 How many moles of HCl are required to produce four moles of AlCl¬3? 3 6 12 18 What is a mole ratio? The fraction a chemist uses to convert the amount of reactant from grams to moles A numerical relationship between the molar masses of the reactants involved in a particular reaction A proportional comparison of the number of moles of different substances that participate in a chemical reaction A comparison of moles of each reactant involved in a chemical reaction to determine which is limiting. In the following equation: 12 HClO4 + P4O10 → 4 H3PO4 + 6 Cl2O73PO4 to HClO4? 1:3 (or 4:12) 2:3 (or 4:6) 1:4 3:1 In the equation: 2 Na3P + 3 CaF2 -> 6 NaF + Ca3P2 How many moles of Na3P must react with 12 moles of CaF2 to use all the reactant up? 8 2 3 6 Another way of making ammonia, besides the Haber-Bosch process, is to combine barium nitride with water, according to the equation: Ba3N2 + 6 H2O → 3 Ba(OH>2 + 2 NH3 If you want to make 100 moles of ammonia, how many moles of barium nitride do you need? 25 50 100 300 Once you’ve obtained the ammonia, you could use it to manufacture nitrous oxide (otherwise known as laughing gas), according to the equation: 4 NH3 + 5 O2 → 4 NO + 6 H2O True or false: If you have 20 moles each of ammonia and oxygen, ammonia is the True False I'm not sure Why is stoichiometry important to a manufacturer who makes chemical products? It tells the manufacturer which reactant will be more expensive It allows the manufacturer to think of amounts of chemicals in moles rather than by weight It gives the manufacturer information about how to make the reaction proceed most efficiently It allows the manufacturer to predict the amount of product to expect from the amount of starting material Silver chloride is an antiseptic substance that is used in some bandages and deodorants. Let’s say you are planning to produce silver chloride for a bandage maker, according to the chemical equation: KCI + AgNO3 → AgCl + KNO3 If you want to be sure that all the AgNO3 is used up, so you will make ______ the limiting reactant by adding _________ of it than the other reactant (given that the mole ratio is 1:1). KCI, less KCI, more AgNO3, less AgNO3, more Score Quiz