Lecture 0403 Displacement Reactions, Molarity, Stoichiometric Calcs.

Transcription

1 Chemistry, The Central Science, 11th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten Lecture 0403 Displacement, Molarity, Stoichiometric Calcs. John D. Bookstaver St. Charles Community College Cottleville, MO

2 Quick Quiz #11 (See your facilitator)

3 Displacement In displacement reactions, ions oxidize an element. The ions, then, are reduced.

4 Oxidizing and Reducing Agents The oxidizing reagent is reduced! The reducing agent is oxidized! The entire species, not just the atom. Example: Permanganate ion,mno 4-,is an oxidizing agent, not Mn +7

5 Displacement In this reaction, silver ions oxidize copper metal. Cu (s) + 2 Ag + (aq) Cu 2+ (aq) + 2 Ag (s)

6 Displacement The reverse reaction, however, does not occur. Cu 2+ (aq) + 2 Ag (s) x Cu (s) + 2 Ag + (aq)

7 Activity Series

8 Practice Exercise 4.8 Which of the following metals will be oxidized by Pb(NO 3 ) 2 : Zn, Cu, Fe?

9 Molarity Two solutions can contain the same compounds but be quite different because the proportions of those compounds are different. Molarity is one way to measure the concentration of a solution. Molarity (M) = moles of solute volume of solution in liters

10 Mixing a Solution To create a solution of a known molarity, one weighs out a known mass (and, therefore, number of moles) of the solute. The solute is added to a volumetric flask, and solvent is added to the line on the neck of the flask.

11 Practice Exercise 4.9 Calculate the molarity of a solution made by dissolving 5.00 g of glucose (C 6 H 12 O 6 ) in sufficient water to form exactly 100 ml of solution.

12 Practice Exercise 4.10 a) How many grams of Na 2 SO 4 are there in 15 ml of 0.50 M Na 2 SO 4? (b) How many milliliters of 0.50 M Na 2 SO 4 solution are needed to provide mol of this salt?

13 Dilution One can also dilute a more concentrated solution by Using a pipet to deliver a volume of the solution to a new volumetric flask, and Adding solvent to the line on the neck of the new flask.

14 Dilution The molarity of the new solution can be determined from the equation M c V c = M d V d, where M c and M d are the molarity of the concentrated and dilute solutions, respectively, and V c and V d are the volumes of the two solutions.

15 Practice Exercise 4.11 (a) What volume of 2.50 M lead(ii) nitrate solution contains mol of Pb 2+? (b) How many milliliters of 5.0 M K 2 Cr 2 O 7 solution must be diluted to prepare 250 ml of 0.10 M solution? (c) If 10.0 ml of a 10.0 M stock solution of NaOH is diluted to 250 ml, what is the concentration of the resulting stock solution?

16 Using Molarities in Stoichiometric Calculations

17 Titration Titration is an analytical technique in which one can calculate the concentration of a solute in a solution.

18 Practice Exercise 4.12 a) How many grams of NaOH are needed to neutralize 20.0 ml of M H 2 SO 4 solution? (b) How many liters of M HCl(aq) are needed to react completely with mol of Pb(NO 3 ) 2 (aq), forming a precipitate of PbCl 2 (s)?

19 Practice Exercise 4.13 A sample of an iron ore is dissolved in acid, and the iron is converted to Fe 2+. The sample is then titrated with ml of M MnO 4 solution. The oxidation-reduction reaction that occurs during titration is as follows: MnO 4 - (aq) + 5 Fe 2+ (aq) + 8 H + (aq) Mn 2+ (aq) + 5 Fe 3+ (aq) + 4 H 2 O(l) (a) How many moles of MnO 4 were added to the solution? (b) How many moles of Fe 2+ were in the sample? (c) How many grams of iron were in the sample? (d) If the sample had a mass of g, what is the percentage of iron in the sample?

20 Practice Exercise 4.14 What is the molarity of an NaOH solution if 48.0 ml is needed to neutralize 35.0 ml of M H 2 SO 4?