1. Solution Concentration Chapter 4 Reactions in Aqueous Solutions (part 2)

2. Copyright © Cengage Learning. All rights reserved. 4 | 2 Molar Concentration, Molarity, (M) Moles of solute per liter of solution

3. Copyright © Cengage Learning. All rights reserved. 4 | 3 To prepare a solution, add the measured amount of solute to a volumetric flask, then add water to bring the solution to the mark on the flask.

4. 4 Solution Stoichiometry The concentration of a solution is the amount of solute present in a given quantity of solvent or solution. M = molarity = moles of solute liters of solution What mass of KI is required to make 500. mL of a 2.80 M KI solution? volume of KI solutionmoles KIgrams KI M KI 500. mL= 232 g KI 166 g KI 1 mol KI x 2.80 mol KI 1 L soln x 1 L 1000 mL x

5. 5 Preparing a Solution of Known Concentration

6. 6 Dilution is the procedure for preparing a less concentrated solution from a more concentrated solution. Dilution Add Solvent Moles of solute before dilution (i) Moles of solute after dilution (f) = MiViMiVi MfVfMfVf =

7. Copyright © Cengage Learning. All rights reserved. 4 | 7

8. Copyright © Cengage Learning. All rights reserved. 4 | 8 You place a 1.52−g of potassium dichromate, K 2 Cr 2 O 7, into a 50.0−mL volumetric flask. You then add water to bring the solution up to the mark on the neck of the flask. What is the molarity of K 2 Cr 2 O 7 in the solution? Molar mass of K 2 Cr 2 O 7 is 294 g. 0.103 M

9. Copyright © Cengage Learning. All rights reserved. 4 | 9 A solution of sodium chloride used for intravenous transfusion (physiological saline solution) has a concentration of 0.154 M NaCl. How many moles of NaCl are contained in 500.−mL of physiological saline? How many grams of NaCl are in the 500.−mL of solution?

10. 10 How would you prepare 60.0 mL of 0.200 M HNO 3 from a stock solution of 4.00 M HNO 3 ? M i V i = M f V f M i = 4.00 M M f = 0.200 MV f = 0.0600 L V i = ? L V i = MfVfMfVf MiMi = 0.200 M x 0.0600 L 4.00 M = 0.00300 L = 3.00 mL Dilute 3.00 mL of acid with water to a total volume of 60.0 mL.

11. Copyright © Cengage Learning. All rights reserved. 4 | 11 A saturated stock solution of NaCl is 6.00 M. How much of this stock solution is needed to prepare 1.00−L of physiological saline soluiton (0.154 M)?

12. Copyright © Cengage Learning. All rights reserved. 4 | 12 Quantitative Analysis The determination of the amount of a substance or species present in a material.

13. Copyright © Cengage Learning. All rights reserved. 4 | 13 Gravimetric Analysis A type of quantitative analysis in which the amount of a species in a material is determined by converting the species to a product that can be isolated completely and weighed.

14. 14 Gravimetric Analysis 1.Dissolve unknown substance in water 2.React unknown with known substance to form a precipitate 3.Filter and dry precipitate 4.Weigh precipitate 5.Use chemical formula and mass of precipitate to determine amount of unknown ion

15. Copyright © Cengage Learning. All rights reserved. 4 | 15 The figure on the right shows the reaction of Ba(NO 3 ) 2 with K 2 CrO 4 forming the yellow BaCrO 4 precipitate.

16. Copyright © Cengage Learning. All rights reserved. 4 | 16 The BaCrO 4 precipitate is being filtered in the figure on the right. It can then be dried and weighed.

17. Copyright © Cengage Learning. All rights reserved. 4 | 17 A soluble silver compound was analyzed for the percentage of silver by adding sodium chloride solution to precipitate the silver ion as silver chloride. If 1.583 g of silver compound gave 1.788 g of silver chloride, what is the mass percent of silver in the compound?

18. Copyright © Cengage Learning. All rights reserved. 4 | 18 = 1.346 g Ag in the compound = 85.03% Ag Molar mass of silver chloride (AgCl) = 143.32 g

19. Copyright © Cengage Learning. All rights reserved. 4 | 19 Titration A procedure for determining the amount of substance A by adding a carefully measured volume with a known concentration of B until the reaction of A and B is just complete.

20. 20 Titrations In a titration a solution of accurately known concentration is added gradually added to another solution of unknown concentration until the chemical reaction between the two solutions is complete. Equivalence point – the point at which the reaction is complete Indicator – substance that changes color at (or near) the equivalence point Slowly add base to unknown acid UNTIL the indicator changes color

21. Copyright © Cengage Learning. All rights reserved. 4 | 21 In the titration above, the indicator changes color to indicate when the reaction is just complete.

22. Copyright © Cengage Learning. All rights reserved. 4 | 22 Volumetric Analysis A type of quantitative analysis based on titration.

23. 23 Titrations can be used in the analysis of Acid-base reactions Redox reactions H 2 SO 4 + 2NaOH 2H 2 O + Na 2 SO 4 5Fe 2+ + MnO 4 - + 8H + Mn 2+ + 5Fe 3+ + 4H 2 O

24. 24 What volume of a 1.420 M NaOH solution is required to titrate 25.00 mL of a 4.50 M H 2 SO 4 solution? WRITE THE CHEMICAL EQUATION! volume acidmoles redmoles basevolume base H 2 SO 4 + 2NaOH 2H 2 O + Na 2 SO 4 4.50 mol H 2 SO 4 1000 mL soln x 2 mol NaOH 1 mol H 2 SO 4 x 1000 ml soln 1.420 mol NaOH x 25.00 mL = 158 mL M acid rxn coef. M base

25. Copyright © Cengage Learning. All rights reserved. 4 | 25 Zinc sulfide reacts with hydrochloric acid to produce hydrogen sulfide gas: ZnS(s) + 2HCl(aq)  ZnCl 2 (aq) + H 2 S(g) How many milliliters of 0.0512 M HCl are required to react with 0.392 g ZnS?

26. Copyright © Cengage Learning. All rights reserved. 4 | 26 Molar mass of ZnS = 97.45 g = 0.157 L = 157 mL HCl solution

27. Copyright © Cengage Learning. All rights reserved. 4 | 27 A dilute solution of hydrogen peroxide is sold in drugstores as a mild antiseptic. A typical solution was analyzed for the percentage of hydrogen peroxide by titrating it with potassium permanganate: 5H 2 O 2 (aq) + 2KMnO 4 (aq) + 6H + (aq)  8H 2 O(l) + 5O 2 (g) + 2K + (aq) + 2Mn 2+ (aq) What is the mass percent of H 2 O 2 in a solution if 57.5 g of solution required 38.9 mL of 0.534 M KMnO 4 for its titration?

28. Copyright © Cengage Learning. All rights reserved. 4 | 28 Molar mass of H 2 O 2 = 34.01 g = 1.77 g H 2 O 2 = 3.07% H 2 O 2