CHE-122 Written Assignment 7 PDF

Preview

Summary

WA7...

Description

Name: College ID: Thomas Edison State University General Chemistry II with Labs (CHE-122) Section no.: OL009 Semester and year: JUN2018

Written Assignment 7: Lewis Acids and Bases Answer all assigned questions and problems, and show all work. 1. Oxalic acid (C2H2O4) has the following structure:

An oxalic acid solution contains the following species in varying concentrations: C2H2O4, C2HO4–, C2O42–, and H+. a. Draw Lewis structures of C2HO4– and C2O42–. (5 points) C2HO4–

1 Copyright © 2017 by Thomas Edison State University. All rights reserved.

C2O42–

b. Which of the above four species can act only as acids, which can act only as bases, and which can act as both acids and bases? (5 points) C2H2O4 and H+ can be acids. C2O42– Can be base C2HO42– Can be both acid and base (Reference: Chang 15.7)

2. Classify each of the following species as a Lewis acid or a Lewis base: (a) CO2, (b) H2O, (c) I–, (d) SO2 , (e) NH3, (f) OH–, (g) H+, (h) BCl3. (24 points) a. Lewis Acid b. Lewis Base c. Lewis Base d. Lewis Acid e. Lewis Base f. Lewis Base g. Lewis Acid h. Lewis Acid (Reference: Chang 15.93)

2 Copyright © 2017 by Thomas Edison State University. All rights reserved.

3. Describe the following reaction in terms of the Lewis theory of acids and bases: (4 points) AlCl3(s) + Cl–(aq) → AlCl4–(aq) AlCl3 is considered a Lewis acid since it as an acceptor of an electron pair. Cl- donates an electron pair to the AlCl3, hence making it a Lewis Base. (Reference: Chang 15.94)

4. Which would be considered a stronger Lewis acid: (a) BF3 or BCl3, (b) Fe+2 or Fe+3? Explain. (4 points) a. BF3 is the stronger Lewis acid. b. Fe+3 is the stronger Lewis acid. (Reference: Chang 15.95)

5. Complete the following statements for the complex ion [Co(en)2(H2O)CN]2+. (16 points)\ a. en is the abbreviation for: enthylendiamine b. The oxidation number of Co is: +3 c. The coordination number of Co is: 6 d. En is a bidentate ligand. (Reference: Chang 23.11)

6. Give the oxidation numbers of the metals in the following species: (12 points) a. K3[Fe(CN)6]: CN -1 Fe +3 K +1 b. K3[Cr(C2O4)3]: C2O4 -2 Cr +3 K +1 2– c. [Ni(CN)4] : CN -1 Ni +2 (Reference: Chang 23.13) 3 Copyright © 2017 by Thomas Edison State University. All rights reserved.

7. What are the systematic names for the following ions and compounds? (12 points) a. [Co(NH3)4Cl2]+ Tetraamminedichlorocobalt (III) chloride b. Cr(NH3)3Cl3 Triamminetrichlorochromium(III) chloride c. [Co(en)2Br2]+ Dibromideobisethylenediammine cobalt(III) ion d. [Co(NH3)6]Cl3 Hexaminecobalt(III) chloride

(Reference: Chang 23.15)

8. Write the formulas for each of the following ions and compounds: (12 points) a. tetrahydroxozincate(II) [Zn(OH)4]2b. pentaaquochlorochromium(III) [Cr(H2O)5Cl]3c. tetrabromocuprate(II) [Cu(Br)4]2d. ethylenediaminetetraacetatoferrate(II) [Fe(EDTA)]2(Reference: Chang 23.17)

9. Oxalic acid, H2C2O4, is sometimes used to clean rust stains from sinks and bathtubs. Explain the chemistry underlying this cleaning action. (3 points) The oxalic acid is reacting with the iron (rust) and is forming Fe2(C2O4)3 and becomes soluble in water, meaning it can be washed off. (Reference: Chang 23.41)

10. The label of a certain brand of mayonnaise lists EDTA as a food preservative. How does EDTA prevent the spoilage of mayonnaise? (3 points) EDTA, more commonly calcium EDTA is used as a food preservative that targets the oils and fats in that mayonnaise and stabilizes the mixtures. EDTA has a seemingly 4 Copyright © 2017 by Thomas Edison State University. All rights reserved.

benign impact in small amounts, but it’s long term affects are not fully known. It also appears the only real benefit of EDTA in mayonnaise is to limit the separation of the food while it sits on store shelves, which may make the product look less appealing to a customer. http://www.eatingrealfood.com/articles/edta-a-preservative-in-your-mayonnaise/ (Reference: Chang 23.66)

5 Copyright © 2017 by Thomas Edison State University. All rights reserved....