test3c98

CH3410, Test 3 (20 points), C98

1. (10 points) The Pourbaix Diagram for a hypothetical element, E, is shown below. Various regions are labelled with letters. Below the diagram are listed species formed by E under various conditions of pH and potential in aqueous solut ion. Below the formula for each species, write the letter of the region in which it should occur in the diagram.

E H₂E HEO₄^- H₂EO₃ EO₄^2- HE^- EO EO₃^2- HEO₃^- E^2-

g h a c b i f e d j

2. (5 points) Write a balanced half reaction for reduction of H₂EO₃ at pH 2, and estimate the standard reduction potential.

H₂EO₃ + 2H⁺ + 2e ---> EO + 2H₂O

e ^o = 0.35 V (value of potential at pH = 0).

3. (5 points) Develop Lewis structures for EO₃^2- and EO₄^2-, and determine stereochemistry at E.

Structures:

In EO₃^2-, stereochemistry at E is trigonal pyramidal (4 electron groups, one lone pair and three attaching atoms). In EO₄^2-, it is tetrahedral (4 electron groups, all attaching atoms)

E	H₂E	HEO₄^-	H₂EO₃	EO₄^2-	HE^-	EO	EO₃^2-	HEO₃^-	E^2-
g	h	a	c	b	i	f	e	d	j