1 Chapter 7 Solutions 7.6 Solution Stoichiometry Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

2 Molarity in Chemical Reactions In a chemical reaction, the volume and molarity of a solution are used to determine the moles of a reactant or product. molarity ( mole ) x volume (L) = moles 1 L if molarity (mole/L) and moles are given, the volume (L) can be determined moles x 1 L = volume (L) moles

3 Using Molarity of Reactants How many mL of 3.00 M HCl are needed to completely react with 4.85 g CaCO 3 ? 2 HCl(aq) + CaCO 3 (s) CaCl 2 (aq) + CO 2 (g) + H 2 O(l) STEP 1 Given 3.00 M HCl; 4.85 g CaCO 3 Need volume in mL STEP 2 Plan g CaCO 3 mole CaCO 3 mole HCl mL HCl

4 Using Molarity of Reactants (cont.) 2 HCl(aq) + CaCO 3 (s) CaCl 2 (aq) + CO 2 (g) + H 2 O(l) STEP 3 Equalitites 1 mole CaCO 3 = g; 1 mole CaCO 3 = 2 mole HCl 1000 mL HCl = 3.00 mole HCl STEP 4 Set Up 4.85 g CaCO 3 x 1 mole CaCO 3 x 2 mole HCl x 1000 mL HCl g CaCO 3 1 mole CaCO mole HCl = 32.3 mL HCl required

5 Learning Check How many mL of a M Na 2 S solution are needed to completely react 18.5 mL of M NiCl 2 solution? NiCl 2 (aq) + Na 2 S(aq) NiS(s) + 2 NaCl(aq) 1) 4.16 mL 2) 6.24 mL 3) 27.0 mL

6 Solution 3) 27.8 mL L x mole NiCl 2 x 1 mole Na 2 S x 1000 mL 1 L 1 mole NiCl mole = 27.0 mL Na 2 S solution

7 Learning Check If 22.8 mL of M MgCl 2 is needed to completely react 15.0 mL of AgNO 3 solution, what is the molarity of the AgNO 3 solution? MgCl 2 (aq) + 2 AgNO 3 (aq) 2 AgCl(s) + Mg(NO 3 ) 2 (aq) 1) M 2) M 3) M

8 Solution 3) M AgNO L x mole MgCl 2 x 2 mole AgNO 3 x 1 P 1 L 1 mole MgCl L = mole/L = M AgNO 3

9 Learning Check How many liters of H 2 gas at STP are produced when Zn react with 125 mL of 6.00 M HCl? Zn(s) + 2 HCl(aq) ZnCl 2 (aq) + H 2 (g) 1) 4.20 L H 2 2) 8.40 L H 2 3) 16.8 L H 2

10 2) 8.40 L H 2 gas L x 6.00 mole HCl Solution 2) 8.40 L H 2 gas L x 6.00 mole HCl x 1 mole H 2 x 22.4 L 1 L 2 mole HCl 1 mole = 8.40 L H 2 gas