6-LeChatelier-Complete - LeChateliers Principle Disturbing...

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LeChatelier ʼ s Principle – Disturbing Chemical Equilibria Assignment & Report Guidelines READING Experiment – Lab Handout Download Chemistry , 5 th ed. by Silberberg: Section 17.6 PRE-LAB For each system, prepare a table like the one below in your lab notebook with your predictions about the effect of each addition in each test tube. Leave one full page in your notebook for each of the four systems. The table should take up about ¾ of the page. System #__ Data Table Equilibrium System: In this space, write the primary reaction studied for the system. Test Tube # Condition Change Predicted Outcome Experimental Observation Explanation * * Leave a lot of room to write in the explanation. This will be where you will discuss: Whether what the condition change has resulted in the addition or removal of a reactant or product. This may differ from your prediction. If so, briefly discuss. How competing equilibria interact (if applicable). Other factors affecting the equilibrium. MINI-REPORT For each system, your mini-report will be composed of the complete Data & Analysis Table and answers to any discussion questions included on the procedure page for the system. Include one row for each condition change in the procedure for a system.
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System 1: Acid / Base Equilibria and the pH indicator Methyl Violet Background Acid-Base indicators are chemical compounds that have one form under more acidic conditions, and a different form under more basic conditions. The two forms of the indicator have different colors. Consider the familiar acid-base indicator, phenolphthalein. In its “protonated” form – which is dominant in acidic or neutral solution, it is clear. However, in basic solution, its pink “deprotonated” form dominates. The reaction between the protonated and deprotonated forms is an equilibrium. In solution, the phenolphthalein is never fully protonated or deprotonated. Let’s consider the reaction as follows: clear (in more acidic solutions) pink (in more basic solutions) This equilibrium shifts to the right or the left, based on the concentration of H + in the solution it is in. If the system is at equilibrium under basic conditions and significant H + is added, the reaction will shift to the left to use up the extra H + that was added to the solution and establish a new equilibrium condition. If enough H + is added, then most of the phenolphthalein will be converted to its protonated form, and the pink color of the anion form will no longer be noticeable because it will be at such a low concentration. This shift is not permanent.
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6-LeChatelier-Complete - LeChateliers Principle Disturbing...

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