Chemical Equilibrium Lab

Introduction:

Chemical equilibrium is when the concentrations of the reactants and products have reached a state where reactions occurring in one direction are at the same rate of reactions occurring in the opposite direction. This process, called dynamic equilibrium, is the main subject of Le Chatelier’s Principle.
Le Chatelier pointed out that if a system at equilibrium is subjected to a stress that momentarily causes the system to be not in equilibrium, a spontaneous change will occur to bring the system back to equilibrium. 1 The spontaneous change will always go against the direction of the original shift. The shift could be a change in number factors like:
Temperature, concentration, or pressure when the reactants or products are
gaseous substances.
The purpose of lab Q is to study the affect of temperature and concentrations on the shift of chemical equilibriums.
In the first and second parts of the lab, we will examine changes in the chemical equilibriums primarily due to shifts in the concentrations of products or reactants. In the third part of the experiment, we will examine both the effect of concentration and temperature on the making of a chemical equilibrium.
In Part A of the experiment, we experimented with two equilibrium reactions.
The first one is Chromate/Dichromate equilibrium: 2CrO42- +2 H+ ⇌ Cr2O72- + H2O
The color of the reactant CrO42- is neon yellow and the color of the product Cr2O72- is orange (the color of these ions could tell us if the reaction shift left or right depending on the equilibrium color). In one test tube containing the chemical equilibrium of chromate/ dichromate, we will add NaOH while in another we will add KCl.
The second part involves the equilibrium and forming of Ferric thiocyanate complex ion: Fe3+ + SCN- ⇌ FeSCN2+

The color of the reactants Fe3+and SCN- are neon yellow and colorless respectively. The color of the product FeSCN2+ however is blood red. In five test tubes, one will be the control and four will be the experiments. In the four experiment test tubes, we will put Fe(NO3)3, KSCN, KNO3 and water among the equilibrium of Ferric thiocyanate complex ion
respectively.
The general rule for calculating the rates and equilibrium constants (Kc) could be calculated using the equilibrium constant expression as long as the temperature stays the same: [C]c[D]d =Kc (1) [A]a[B]b

In part B of the experiment, we experimented with Sparingly Soluble Salts, Silver Chloride ( AgCl) in three different ways.
The general equilibrium reaction is: AgCl ⇌ Ag+ + Cl-
Because AgCl is a solid, it isn’t included in equation (1) for calculating K or Ksp. Ksp = [Ag+][Cl-]
Ksp is called the solubility product constant and it is different only in the sense that it regards solubility of the solutions when there is a solid as well.
The silver chloride equilibrium will be put into a test tube and centrifuged so that the denser solids will be on the bottom. In two other test tubes, we will put 1 ml of liquid from the first test tube. In these two test tubes we will introduce HCl and HNO3 respectively while in the one containing the precipitate we will introduce NH3.

Through the experimenting with this equilibrium we can find if the reaction was endothermic or exothermic since we have the colors of the equilibrium shifting right and equilibrium shifting left for this reaction.