1. Thursday February 7, 2013 (Discussion and WS – Limiting Reactant)

2. Bell Ringer Thursday, 2-7-13 A baker has a recipe for a cake that calls for the following ingredients: 4 cups of flour 2 cups of sugar 1 tsp of baking soda 1 tsp of baking powder 1 cup of milk The baker finds she has the following supplies in her store room: 17 cups of flour 9 cups of sugar 6 tsp of baking soda 5 tsp of baking powder 3 cups of milk Without going to the grocery store, how many cakes can she make? 3

3. Announcements National Wave All Your Fingers At Your Neighbor's Day!

4. Announcements I will be available after school today until 5:00.

5. Assignment Currently Open Summative or Formative? Date Issued Date Due Date Into GradeSpeed Final Day QUIZ 16S11/18 1/24 TODAY WS – Mole to Mass Stoichiometry F111/302/1 TOMORROW WS – Mass to Mole Stoichiometry F121/312/5 TOMORROW QUIZ 17S22/1 2/15 WS – Mass to Mass Stoichiometry F132/42/8 TOMORROW Activity - Using Stoichiometry to Prove the Law of Conservation of Mass F142/5 TOMORROW

6. In the laboratory, a reaction is rarely carried out with exactly the required amounts of each of the reactants. In most cases, one or more reactants is present in excess; that is, there is more than the exact amount required to react. Once one of the reactants is used up, no more product can be formed. Limiting Reactant

7. The substance that is completely used up first in a reaction is called the limiting reactant. The limiting reactant is the reactant that limits the amounts of the other reactants that can combine and the amount of product that can form in a chemical reaction. The substance that is not used up completely in a reaction is sometimes called the excess reactant. Limiting Reactant

8. Consider the reaction between carbon and oxygen to form carbon dioxide. C + O 2 → CO 2 According to the equation, one mole of carbon reacts with one mole of oxygen to form one mole of carbon dioxide. Suppose you could mix 5 mol of C with 10 mol of O 2 and allow the reaction to take place. Limiting Reactant

9. The figure below shows that there is more oxygen than is needed to react with the carbon. Carbon is the limiting reactant in this situation, and limits the amount of CO 2 that is formed. Oxygen is the excess reactant, and 5 mol of O 2 will be left over at the end of the reaction.

10. Sample Problem Silicon dioxide (quartz) is usually quite unreactive, but reacts readily with hydrogen fluoride according to the following equation: SiO 2 + 4HF → SiF 4 + 2H 2 O If 2.0 mol of HF are exposed to 4.5 mol of SiO 2, which is the limiting reactant? Answer - The given amount of either reactant is used to calculate the required amount of the other reactant. The calculated amount is then compared with the amount actually available, and the limiting reactant can be identified. We will choose to calculate the moles of SiO 2 required by the given amount of HF. Limiting Reactant

11. Sample Problem SiO 2 + 4HF → SiF 4 + 2H 2 O Under ideal conditions, the 2.0 mol of HF will require 0.50 mol of SiO 2 for complete reaction. Because the amount of SiO 2 available (4.5 mol) is more than the amount required (0.50 mol), the limiting reactant is HF.

12. Worksheet Limiting Reactant