Oxidation States of Vanadium

 

 

Hazards: 

Ammonium vanadate powder is extremely toxic (health hazard rating 4).  Work with dry vanadate powder in the hood.  Protect yourself from inhalation, contact and ingestion. 

The ammonium meta vanadate solution in 3M sulfuric acid is toxic and corrosive.

Chemicals and Solutions: 

0.1 M Ammonium meta-vanadate solution

sodium (meta) bisulfite solid

Granular zinc

0.5% Hydrogen peroxide (make fresh) - about 100 ml

Distilled water

Materials: 

Three 250 ml glass stoppered Erlenmeyer flasks

Short stem funnel with glass wool

Eyedropper

Procedure: 

Cover the bottom of one flask with zinc (excess!).  Add about 50 ml YELLOW NH4VO3 stock solution.  PATIENCE! Hold up and swirl so that students can see color change from YELLOW to BLUE to GREEN to PURPLE. Be sure that reaction is complete. Set aside for a few minutes before doing step 3. Meanwhile go to step 2.

Add 50 ml of YELLOW NH4VO3 stock solution to next flask. Reduce with solid sodium bisulfite until the color turns BLUE.

Pour a little of the PURPLE solution though glass wool (to avoid getting zinc granules in) into the next flask. Oxidize with dilute (0.5%) H2O2 to get GREEN. If color is too intense to see the color change, add water.

YELLOW 

VO3-     (+5)

BLUE 

VO2+ or VO(H2O)52+ (+4)

GREEN

V3+  or V(H2O)63+  (+3)

PURPLE

V2+  or V(H2O)62+  (+2)

Hint: 

Solutions Prep:

0.1M ammonium m-vanadate: dissolve 5.8 g NH4VO3 in 500 mL of 3M sulfuric acid.


Discussion: 

Reactions:

Step 1:  2VO3- (aq) + Zn (s) + 8H+(aq) ---> 2VO2+(aq) + Zn2+(aq) +4H2O

yellow                                        blue

2VO2+(aq) + Zn + 4H+(aq) ---> 2V3+(aq) + Zn2+(aq)+ 2H2O

             blue                                            green

2V3+(aq) + Zn  ----> 2V2+ (aq) +  Zn2+ (aq)

green                       purple

Step 2:  2VO3- (aq) + SO32-(aq) + 6H+(aq) ---> 2VO2+(aq)  +SO42-(aq) + 3H2O

yellow                                                       Blue

Step 3:  2V2+ (aq) + H2O2 (aq) + 2H+(aq) ---> 2V3+(aq) + 2H2O

purple                                               green                             

To schedule a demonstration, please send an email to the demonstration lab.

 

Contact:

Eric Camp

Lecture Demonstration Technician

Bagley Hall 171

(206) 543-1606

ericcamp@uw.edu

 

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