Living By Chemistry SECOND EDITION Unit 4 TOXINS
Living By Chemistry SECOND EDITION Unit 4: TOXINS Stoichiometry, Solution Chemistry, and Acids and Bases
Lesson 91: Mole to Mole Ratios
Chem. Catalyst One way to remove potentially toxic substances from a water source is to precipitate out the harmful ions. Consider the removal of copper ions by precipitation. 2 Na. OH(aq) + Cu(NO 3)2(aq) 2 Na. NO 3(aq) + Cu(OH)2(s) Suppose you add 100 m. L of 0. 10 M Na. OH(aq) to 100 m. L of 0. 10 M Cu(NO 3)2(aq). 1. Have you added equal numbers of moles of the two substances? Explain your thinking. 2. Have you added equal numbers of grams of the two substances? Explain your thinking. 3. Have you added enough Na. OH(aq) to remove all the copper from the solution? Explain your thinking.
Key Question How can you convert all the reactants to products?
You will be able to: • define a mole ratio • explain how to combine reactants in order to make the most product from a reaction • identify a limiting reactant
Prepare for the Lab Work in groups of four. Wear safety goggles at all times. Sodium hydroxide, Na. OH, is corrosive. Do not get any on skin or near eyes. In case of spills, rinse with large amounts of water.
Discussion Notes The coefficients in chemical equations indicate how many counting units (such as moles) of each reactant combine and how many counting units of each product formed in a single reaction. Coefficients in chemical equations always refer to the number of units (molecules, ions, moles) that are combining.
Discussion Notes (cont. ) The mole ratios are the proportions in which two substances (reactants, products, or both) combine or form. Mole ratio: The ratio represented by the coefficients in a chemical equation showing how many units of each substance must combine to make the maximum amount of product. When reactants are not combined in their exact mole ratios, one of the reactants runs out and the other is left over.
Wrap Up How can you convert all the reactants to products? • Coefficients in chemical equations represent the proportions in which reactants combine and products form. This proportion is also called the mole ratio. • If reactants are not combined in their mole ratio, one will run out and the other will be excess. The one that runs out is called the limiting reactant.
Check-In The reaction to form silver phosphate, Ag 3 PO 4(s), is given by this chemical equation: Ag. NO 3(aq) + Na 3 PO 4(aq) Ag 3 PO 4(s) + Na. NO 3(aq) 1. Balance the equation. 2. Which combination of reactants results in the maximum amount of product? a. 1. 0 g Ag. NO 3 to 1. 0 g Na 3 PO 4 b. 3. 0 g Ag. NO 3 to 1. 0 g Na 3 PO 4 c. 1. 0 mole Ag. NO 3 to 1. 0 mole Na 3 PO 4 d. 3. 0 moles Ag. NO 3 to 1. 0 mole Na 3 PO 4
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