Why is potassium chromate yellow

Debra Myers, Mulac, Schulze, Smith

Lab Group #3

04/06/2016

Le Châtlier’s Principle

Purpose/Objective:

Investigate Le Châtlier’s principle on chromate and dichromate equilibrium and also investigate the positions and reactions of the Potassium Chromate and /Potassium ferrocyanide and Iron (III) Nitrate.

Procedure:

Exercise 1: Equilibrium of Chromate and Dichromate

1.Sat my well plate on the table, then I snipped the tip off the Potassium Chromate and placed it upright position inside one of the 24 wells as a holder. 2. Placed 8 drops of Potassium Chromate inside the well in front of where I was holding my pipet. 3. Observed and recorded the color it changed to in the Data 1 slot of Exercise 1 table. 4. I added drops of hydrochloric acid into it until it changed colors and reached its equilibrium. Then I recorded the number of drops in the table. 5. Recorded the color of the dichromate in to the table. 6. Added drops of Sodium Hydroxide to the potassium chromate and watched until the equilibrium shift positions and color change. Recorded the number of drops of NaOH into the data. 7. I got my ice cold water and my hot water together. 8. Placed 8 drops of Potassium Chromate into an empty well and added 4 drops of HCL into it. 9. Used my empty pipet and drew up the contents into it and held it, so the pipet was right side up. 10. Watched the color and the equilibrium shift and recorded it into the table. 11. Placed the reaction into the cold water for 2-3 mins and after I took it out I observed the equilibrium and color. 12. Recorded the data into the table along with my explanations. 13. I placed the reaction in the Hot Water cup for 2-3 mins and after I took it out; I observed the color and determined the position shift. 14. I recorded the data into the table 2. 15. Clean my equipment and placed the caps on the bottles to use in next experiment.

Exercise 2: Equilibrium of Ferrocyanide and Ferric Ferrocyanide

1. Sat my well plate on the table, then I snipped the tip off the Potassium Ferrocyanide (wipe the scissors with a damped paper towel) and snipped the tip off the Iron (III) Nitrate and placed them upright position inside two of the 24 wells as a holder. 2. Placed 8 drops of potassium ferrocyanide into the empty well and recorded the color in the data table3. 3. Added 1 drop of Iron (III) Nitrate to the potassium ferrocyanide and recorded the color in the table. 4. I added drops of NaOH into it until it reached its equilibrium shift/color change. 5. I recorded the number of drops in the data table. 6. Observed the reaction and recorded my data into the table. 7. Cleaned all my equipment and closed the lids tightly for future use.

Exercise 1: Equilibrium of Chromate and Dichromate

Data Table 1. Chromate-Dichromate.

Color of Chromate

Number of drops of HCl to reach equilibrium

Color of Dichromate

Number of drops of NaOH to shift equilibrium position

Dark yellow

3

Orange

7

Data Table 2. Endothermic and Exothermic Equilibrium Position.

Reaction at Room Temperature

Reaction in Cold Water Bath

Reaction in Hot Water Bath

Color

Red Orange

Bright Orange

Red-Orange

Equilibrium Position

(Left or Right)

Left- towards the reactants

Right-Towards the products

Explanation of why equilibrium is shifted to the left or to the right

There were solid particles on the bottom of the pipet while the liquid maintained the majority of the pipet. So there was a solid potion and liquid potion. potion.

The solution was all liquid, so there were no solid particles. This means the reactants mixed together formed the product.

Questions

A. Use your results to determine if the forward reaction in the potassium chromate/HCl reaction endothermic or exothermic. Explain your answer, using Table 1 to help construct your thoughts.

The Reaction is Endothermic because the substance became more acidic which equals to higher heat energy.

B. Write the equation for the equilibrium constant (K) of the reaction studied in this exercise.

K=(Cr2 O7)(H20)(KCl)2 / (K2 CrO4) (HCL)2

Use the information below to answer Questions C, D, and E:

The equilibrium constant (K) of the reaction below is K = 6.0 x 10-2, with initial concentrations as follows: [H2] = 1.0 x 10-2 M, [N2] = 4.0 M, and [NH3] = 1.0 x 10-4M.

C. If the concentration of the reactant H2 was increased from 1.0 x 10-2 M to 2.5 x 10-1M, calculate the reaction quotient (Q) and determine which way the equilibrium position would shift.

Q=1.6 * 10 (-10 exponent)

D. If the concentration of the reactant H2 was decreased from 1.0 x 10-2 M to 2.7 x 10-4M, calculate the reaction quotient (Q) and determine which way the equilibrium position would shift.

Q=1.270131585632272 * 10 (2 exponent) It will shift left.

E. If the concentration of the product NH3 was decreased from 1.0 x 10-4 M to 5.6 x 10-3M, calculate the reaction quotient (Q) and determine which way the equilibrium position would shift.

Q=7.84 * 10(-4 exponent). It will shift right.

Exercise 2: Equilibrium of Ferrocyanide and Ferric Ferrocyanide

Data Table 3. Ferric Ferrocyanide.

Color of Potassium Ferrocyanide

Color of Ferric Ferrocyanide

Number of drops of NaOH to shift equilibrium position

Observations when equilibrium position is shifted

Light yellow

Dark blue/greenish

4 drops

The dark blue/greenish substance turned brown while the surrounding substance turned yellow.

Questions

A. From your observations and data collected in Data Table 3, describe the direction of the equilibrium position shift upon addition of NaOH.

The equilibrium position would shift left because the product ratio increases when NaOH is added.

24272

Chromate

Dichromate

2KCrO + 2HCl CrO + HO + 2KCl

€

2(g)2(g)3(g)

N + 3H 2NH