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3. A student is studying the equilibrium represented by the equation: 2 CrO42-(aq, yellow) + 2 H3O+(aq) Cr2O72-(aq, orange) + 3 H2O(l) The mixture obtained by the student is yellow.

(1) Describe the color change the student should observe after adding concentrated HCl to the equilibrium mixture. The color change the student should observe after adding concentrated HCl to the equilibrium mixture when Cr2O72- is formed a orange color is observed. When HCl is added to the mixture, HCl ionizes with water to form H3O+ ion so with the addition of HCl, the concentration of reactants increases.

(2) Briefly explain your answer to (1) in terms of Le Châtelier’s principle. According to Le-Châtelier’s principle, if external stress is applied to a system at equilibrium, the system adjusts in such a way that the stress is partially offset and the system reaches a new equilibrium position so, with the increase in concentration of reactants, the equilibrium begins to shift to the right for example towards products this causes an increase in formation of products which are orange in color so on addition of HCl, the student will observe a color change from yellow to orange.

(3) Describe the color change the student should observe after adding solid sodium chromate (Na2CrO4) to the mixture prepared in (1). Recall that Na2CrO4 dissolves in water and dissociates into Na+ and CrO42- ions.

(4) Briefly explain your answer to (3) in terms of Le Châtelier’s principle.

(5) Describe the color change the student should observe after adding excess NaOH solution to the equilibrium mixture in (3).

(6) write a net ionic equation to support your answer to (5).

(7) Briefly explain your answers to (5) in terms of Le Châtelier’s principle.

Chemical Equilibrium - Pre-lab quiz. Please help.

1. How will you be able to tell which way the equilibrium is shifting in the Cr₂O₇^2-/CrO₄^2- equilibrium system?

2. According to Le Chatelier’s Principle, which way will an equilibrium shift (left or right) when heat is added if the reaction in the forward direction is exothermic?

3. In an undisturbed equilibrium system, why do the concentrations of the products and reactants remain constant?

4. In an equilibrium system involving Co(H_2/O)₆²⁺ and NCS^-, how will you decrease the concentration of NCS^- in the mixture?

5. What should you do with the leftover reagents at the end of the experiment?

What can be safety concerns for investing chemical reaction? And what can we do to keep safe form them