# 5.P: Le Chatelier's Principle (Pre-Lab)


1. Cadmium hydroxide, an important component of $$\ce{NiCd}$$ batteries, is only slightly soluble in water.
• Write a reaction for the dissolution of cadmium hydroxide in water.
• Write the $$K_{sp}$$ expression for cadmium hydroxide.
• You add a small amount of $$\ce{NaOH}$$ to a test tube containing cadmium nitrate solution. Initially nothing happens, but as you add more $$\ce{NaOH}$$ you begin to observe the formation of a white, powdery solid that resembles snowflakes. Eventually, all the precipitate settles to the bottom of your test tube. Explain why you do not see the precipitate initially as you first begin to add $$\ce{NaOH}$$ (aq).
• Explain why you eventually do see a precipitate.
• Which of the following two reagents: $$\ce{HNO3}$$ or $$\ce{KOH}$$, do you think will increase the solubility of cadmium hydroxide solution?Explain your answer.
1. The following complex ion formation equilibrium takes place in water:

$\ce{Cu(CN)4^{2-} (aq) + 4 NH3 (aq) <=> Cu(NH3)4^{2+} (aq) + 4 CN^{-} (aq)}$

• Write the $$K_{f}$$ expression for this complex ion reaction
• The color of $$\ce{Cu(CN)4^{2-}}$$ (aq) is light blue, while the color of $$\ce{Cu(NH3)4^{2+}}$$ is violet. Suppose you mix solutions of $$\ce{Cu(NO3)2}$$, $$\ce{NaCN}$$ and $$\ce{NH3}$$ in a test tube and allow the reaction to reach equilibrium. The color of the solution is light blue at this point. Given that the above reaction is endothermic, should you heat the solution, or cool the solution in order to change the color from light blue to violet? Explain your answer using Le Chatelier’s principle.
1. Congo Red ($$CR$$) is a pH indicator which has a blue color in its acidic form and red color in its basic form. When dissolved in water, $$CR$$ forms a red-colored solution.
• Write a reaction for the equilibrium between the two forms of congo red. Use $$HCR$$ for the acidic form and $$CR^{-}$$ for the basic form.
• You make a solution of $$CR$$ in water. Which of the following reagents, 6 M $$\ce{HCl}$$ or 6 M $$\ce{NaOH}$$, will cause the solution to change color? Explain your answer using the concept of coupled reaction.

5.P: Le Chatelier's Principle (Pre-Lab) is shared under a not declared license and was authored, remixed, and/or curated by Santa Monica College.