2. 1 Zinc reacts with acids to produce H 2 gas.Zinc reacts with acids to produce H 2 gas. Have 10.0 g of ZnHave 10.0 g of Zn What volume of 2.50 M HCl is needed to convert the Zn completely? What volume of 2.50 M HCl is needed to convert the Zn completely? SOLUTION STOICHIOMETRY Section 5.10

3. 2 GENERAL PLAN FOR STOICHIOMETRY CALCULATIONS Mass zinc Stoichiometric factor Moles zinc Moles HCl Mass HCl Volume HCl

4. 3 Step 1: Write the balanced equation Zn(s) + 2 HCl(aq) --> ZnCl 2 (aq) + H 2 (g) Step 2: Calculate amount of Zn Zinc reacts with acids to produce H 2 gas. If you have 10.0 g of Zn, what volume of 2.50 M HCl is needed to convert the Zn completely? Step 3: Use the stoichiometric factor

5. 4 Zinc reacts with acids to produce H 2 gas. If you have 10.0 g of Zn, what volume of 2.50 M HCl is needed to convert the Zn completely? Step 4: Calculate volume of HCl req’d

6. 5 ACID-BASE REACTIONS Titrations H 2 C 2 O 4 (aq) + 2 NaOH(aq) ---> acid base acid base Na 2 C 2 O 4 (aq) + 2 H 2 O(liq) Carry out this reaction using a TITRATION. Oxalic acid, H 2 C 2 O 4

7. 6 Setup for titrating an acid with a base CCR, page 186

8. 7 TitrationTitration 1. Add solution from the buret. 2. Reagent (base) reacts with compound (acid) in solution in the flask. 3. Indicator shows when exact stoichiometric reaction has occurred. 4. Net ionic equation H + + OH - --> H 2 O H + + OH - --> H 2 O 5. At equivalence point moles H + = moles OH - moles H + = moles OH -

9. 8 1.065 g of H 2 C 2 O 4 (oxalic acid) requires 35.62 mL of NaOH for titration to an equivalence point. What is the concentra- tion of the NaOH? 1.065 g of H 2 C 2 O 4 (oxalic acid) requires 35.62 mL of NaOH for titration to an equivalence point. What is the concentra- tion of the NaOH? LAB PROBLEM #1: Standardize a solution of NaOH — i.e., accurately determine its concentration.

10. 9 1.065 g of H 2 C 2 O 4 (oxalic acid) requires 35.62 mL of NaOH for titration to an equivalence point. What is the concentration of the NaOH? Step 1: Calculate amount of H 2 C 2 O 4 Step 2: Calculate amount of NaOH req’d

11. 10 1.065 g of H 2 C 2 O 4 (oxalic acid) requires 35.62 mL of NaOH for titration to an equivalence point. What is the concentration of the NaOH? Step 1: Calculate amount of H 2 C 2 O 4 = 0.0118 mol acid = 0.0118 mol acid Step 2: Calculate amount of NaOH req’d = 0.0236 mol NaOH = 0.0236 mol NaOH Step 3: Calculate concentration of NaOH [NaOH] = 0.663 M

12. 11 LAB PROBLEM #2: Use standardized NaOH to determine the amount of an acid in an unknown. Apples contain malic acid, C 4 H 6 O 5. C 4 H 6 O 5 (aq) + 2 NaOH(aq) ---> Na 2 C 4 H 4 O 5 (aq) + 2 H 2 O(liq) Na 2 C 4 H 4 O 5 (aq) + 2 H 2 O(liq) 76.80 g of apple requires 34.56 mL of 0.663 M NaOH for titration. What is weight % of malic acid?

13. 12 76.80 g of apple requires 34.56 mL of 0.663 M NaOH for titration. What is weight % of malic acid? Step 1: Calculate amount of NaOH used. C V = (0.663 M)(0.03456 L) = 0.0229 mol NaOH = 0.0229 mol NaOH Step 2: Calculate amount of acid titrated. = 0.0115 mol acid

14. 13 76.80 g of apple requires 34.56 mL of 0.663 M NaOH for titration. What is weight % of malic acid? Step 3: Calculate mass of acid titrated. Step 1: Calculate amount of NaOH used. = 0.0229 mol NaOH = 0.0229 mol NaOH Step 2: Calculate amount of acid titrated = 0.0115 mol acid = 0.0115 mol acid

15. 14 76.80 g of apple requires 34.56 mL of 0.663 M NaOH for titration. What is weight % of malic acid? Step 1: Calculate amount of NaOH used. = 0.0229 mol NaOH = 0.0229 mol NaOH Step 2: Calculate amount of acid titrated = 0.0115 mol acid = 0.0115 mol acid Step 3: Calculate mass of acid titrated. = 1.54 g acid = 1.54 g acid Step 4: Calculate % malic acid.