Exploring_Equilibria - gExploring Equilibria Chem 112 Name:...

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gExploring Equilibria Name: ANSWER KEY Chem 112 This experiment explores a variety of equilibrium systems. A reference Table of Reactions is attached to aid in your explanations. In this qualitative lab, your observations, predictions, and explanations should be recorded in the spaces provided. Using what you know about equilibria and the Table of Reactions included, you should be able to explain all your observations in terms of the relative sizes of equilibrium constants and LeChatelier’s principle. Because your investigation is qualitative, the exact amounts of the solutions you work with are not critical. You will be transferring around 1 mL of solution, which is about the same as 20 drops. Don’t use much more of any solution. Investigation 1: Chromate-Dichromate Solutions There are two forms of chromium in high oxidation states: chromate ion (CrO 4 2- ) and dichromate ion (Cr 2 O 7 2- ). This experiment explores the equilibrium between them. What to do : 1. Place about 0.5 mL of 1 M potassium chromate solution in a small test tube. Describe the solution. Write a balanced equation for the dissolution of K 2 CrO 4 . K 2 CrO 4 (s) --> 2 K + (aq) + CrO 4 2- (aq) 2. Add a few drops of 3 M sulfuric acid (H 2 SO 4 ). Write your observations. Solution turns from yellow to orange. 3. The chromate anion (CrO 4 2- ) is converted into dichromate ion (Cr 2 O 7 2- ) in the presence of acid. Write a net ionic equation for this reaction. 2 H + (a) + 2 CrO 4 2- (aq) -->  Cr 2 O 7 2- (aq) + H 2 O(l)
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4. Add several drops of 6 M sodium hydroxide (NaOH). Record your observations and write a net ionic equation for what occurs. Turns from yellow back to orange.  There are a couple ways to write this, but best is: 2 OH - (aq) + Cr 2 O 7 2- (aq) --> 2 CrO 4 2- (aq)  +  H 2 O(l) 5. Comment on the reversibility or lack thereof in the reactions converting chromate and dichromate. It is reversible. Investigation 2: Precipitation of Barium Chromate Many but not all barium salts are insoluble. This experiment explores the reactions between Ba 2+ ion and other anions. What to do
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This note was uploaded on 04/12/2011 for the course CHEM 1A taught by Professor Nitsche during the Spring '08 term at University of California, Berkeley.

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Exploring_Equilibria - gExploring Equilibria Chem 112 Name:...

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