Question

1. In a small beaker mix together 5.0 mL of 0.10 M Co(NO3)2 . 6H2O with 5.0 mL of concentrated

HCl. Be sure to mix thoroughly with your glass stirring rod. This is your equilibrium mixture.
2. Place 1.0 mL of your equilibrium mixture in a small test tube add 1.0 mL of concentrated HCl.

Observe any color changes and state in which direction (if any) the equilibrium shifted.

3. Place a new 1.0 mL sample of your equilibrium mixture in a small test tube and add 1.0 mL of deionized water. Observe any color changes and state in which direction (if any) the equilibrium shifted.

4. Place a new 1.0 mL sample of your equilibrium mixture in a small test tube and add 1.0 mL of 0.10 M AgNO3. Observe any color changes and state in which direction (if any) the equilibrium shifted.

5. Place a new 1.0 mL sample of your equilibrium mixture in a small test tube and heat it in a boiling water bath for several minutes. Observe any color changes and state in which direction (if any) the equilibrium shifted.

6. Place a new 1.0 mL sample of your equilibrium mixture in a small test tube and place it in an ice bath for several minutes. Observe any color changes and state in which direction (if any) the equilibrium shifted.

7. When finished place all of your solutions in the waste container, you will be using fresh solutions for part II.

Part II: Solution preparation

1. Obtain a 10 mL graduated cylinder and three, 1 cm diameter spectrophotometer cells

   (cuvettes).

2. Fill one cuvette about 3⁄4 full with deionized water. This cuvette will be used as the blank, to zero

   the instrument.

3. Fill a second cuvette about 3⁄4 full with 0.10 M Co(NO3)2 .6H2O.

4. Prepare 100 mL of a 0.010 M Co(NO3)2 . 6H2O solution. Add exactly 10.0 mL of 0.10 M Co(NO3)2 .

   6H2O to a 100 mL volumetric flask and dilute with deionized water to the mark.

5. Use the 10.0 ml graduated cylinder to prepare a solution of [CoCl4]2-. To the 10 mL graduated

   cylinder add 1.0 mL of 0.010 M Co(NO3)2 * 6H2O (prepared in step 4). Carefully pipette 4.0 mL

   of 12 M HCl into the graduated cylinder so that the total volume is 5 mL. Mix well.

6. Fill the third cuvette about 3⁄4 full with the solution from step 5.

7. Obtain an equilibrium mixture from your instructor. This will be cuvette 4.

Summary Report

Solution	Observed Color	Shift in Equilibrium (right, left, no shift)	Explanation for shift
Equilibrium Mixture plus con. HCl	purple
Equilibrium Mixture plus water	pink
Equilibrium Mixture plus AgNO3	milky pink
Equilibrium Mixture after heating	blue
Equilibrium Mixture after cooling	light purple

Is this reaction endothermic or exothermic? (Hint: Use your results from heating and cooling)

Answer 1

  

Solution	Observed Color	Shift in Equilibrium (right, left, no shift)	Explanation for shift
Equilibrium Mixture plus con. HCl	purple	Right	The reaction taking place is: Co(NO3)2.6H2O + 2 HCl → CoCl2.6H2O + 2 HNO3 The reaction proceeds towards forward direction or towards product formation. With the adition of the Cl- the equilibrium shifts to the right and a purple solution is formed due to the higher concentration of the product, CoCl2.6H2O in the equilibrium solution.
Equilibrium Mixture plus water	pink	Left	When water is added, it shifts to the left (backward direction) and a pink solution is formed due to the higher concentration of Co(NO3)2.6H2O in the equilibrium solution. The shift is observed due to Le Chatelier's principle.
Equilibrium Mixture plus AgNO3	milky pink	Left	When AgNO3 reacts with a chloride salt, the product formed is AgCl as precipitate and the nitrate salt. Therefore, the reaction shifts towards backward direction and there is higher concentration of Co(NO3)2.6H2O along with AgCl precipitate. So, the colour of the solution turns milky pink.
Equilibrium Mixture after heating	blue	Right	When the equilibrium solution was placed into boiling water bath, the solution turned to blue color due to the higher concentration of CoCl2.6H2O as the equilibrium shifts towards forward direction with rise in temperature.
Equilibrium Mixture after cooling	light purple	Left	when placed into an ice bath it turned again to light purple color due to the higher concentration of Co(NO3)2.6H2O as the reaction shifts backwards. This means that reaction is reversible with respect to the temperature.