Confused What is the objective of the following The Effect o

Confused. What is the objective of the following...

The Effect of Concentration

To explore the effect of concentration on a system at equilibrium, the chromate (CrO₄^2-)/dichromate (Cr₂O₇^2-) equilibrium is a good example. Each solution has a distinctive color. The chromate is a bright yellow and the dichromate is orange.

2 CrO₄^2-(aq) + 2 H⁺(aq)‹-> Cr₂O₇^2- (aq) + H₂O (l)                                         

Yellow                                            orange

The color of the solution can be used to determine the dominant species present in the solution. An orange solution, for example, indicates that the solution contains predominately the products of the reaction.

An equilibrium can be established by dissolving a small amount of CrO₄^-2 (as Na₂CrO₄) in water with a few drops of acid. The system will reach equilibrium and the color will stabilize. Depending upon the amount of acid added and the temperature of the solution, the color may be yellow, orange, or something in between. LeChatlier’s principle says that the position of the equilibrium can be shifted by the addition of acid. The prediction is that the addition of the acid would shift the equilibrium to compensate for the acid and produce more Cr₂O₇^2-.

Whether or not this prediction holds true can be determined by looking for the color change. The chemical basis for this prediction relates to the kinetics of the reaction. Increasing the concentration of a substance causes a temporary increase in the reaction rate on that side of the equilibrium. Upon addition of acid, the hydrogen ion concentration increases, and as a result, the chromate and hydrogen ions are converted to products faster than the reverse process. The equilibrium constant for this reaction

                           2 CrO₄^2-(aq) + 2 H⁺(aq)‹-> Cr₂O₇^2- (aq) + H₂O (l)

can be expressed as

                                  [Cr₂O₇^2-]
                         K = ------------------
                                [CrO₄^2-]²[H⁺]²

When the [H⁺] is increased, the value of Q would decrease. In order to reestablish K, the reaction shifts to the right, eventually decreasing the [CrO₄^2-] & [H⁺] and increasing the [Cr₂O₇^2-] until the value of K is restored. The Effect of Temperature

The system used to test the effect of temperature in this experiment is

Co(H₂0)₆²⁺ (aq) + 4 Cl^-(aq) ‹-> 4 CoC1₄^2-(aq) + 6 H₂0 (/)                         

pink                                                  violet

Again, the color will be used to identify the predominant species present. The hexaquocobaltate (II) complex is pink and the tetrachlorocobaltate (II) complex is violet.

Solution

the objective of this to study which speicies is dominant at equlibrium and to verify the Le chatlier principal, that species is dominant, whose color u can see, and le chatlier principal can be verify by intensity of the color of the solution.