• Universiti Teknologi Mara

• CHM 420

Experiment 5 : Chemical Equilibrium Purpose To observe the effects to equilibrium system when certain stresses are introduced Introduction Chemical equilibrium is a reaction in chemical equilibrium when the rate of the forward reaction is equals to the rate of the reverse reaction. In other words, there is no net change in concentrations of reactants and products. When the rate is zero, the net concentrations of A, B, C, and D are in equilibrium with each other. Thus, if there is a change in the system due to changes in concentration, temperature, or pressure, the equilibrium will shift to balance the change and re-establish equilibrium based on Le Chatelier's principle. Le Chatelier's principle states that if an outside influence upsets an equilibrium, the system undergoes a change in a direction that counteracts the disturbing influence and, if possible, returns the system to equilibrium. For example, A + B C + D ⇌ If the concentration of B is increased, the rate of the forward reaction will increase, the concentration of A decreases and the concentration of C and D will increase too. The two rates will become equal after a period of time and the system will be in equilibrium. Chemical Apparatus Concentrated ammonium hydroxide (NH40H) 6M ammonium hydroxide(NH4OH) 0.1M cobalt(II) chloride (CoCl2) Phenolphthalein 0.1M iron(III) chloride (FeCl3) 0.1M potassium thiocyanate (KSCN) 12 M hydrochloric acid (HCl) 3 M silver nitrate (AgNO3) 0.1 M copper(II) sulfate (CuSO4) 3m sulfuric acid (H2SO4) Procedure Part A : Iron (III) chloride plus potassium thiocyanate A stock solution was prepared by adding 1 mL 0.1 M iron (III) chloride and I mL o.1 M potassium thiocyanate solutions to 50 mL of distilled water. They were mixed thoroughly. 5 mL of this stock solution was poured into each of four test tubes. 1. Test tube 1 : As a control for colour comparison. 2. Test tube 2 : About 1 mL of 1.0 M iron(III) chloride solution was added and the colour change was observed. 3. Test tube 3 : About 1 mL of 1.0M potassium thiocyanate solution was poured and the colour change was observed. 4. Test tube 4 : 0.1 M silver nitrate solution were added dropwise (less than 1 mL) until almost all the colour was discharged. The white precipitate consists of AgCl and AgSCN were formed. About half of the contents (including the precipitate) was poured into another tube. 0.1 M potassium thiocyanate solution was added dropwise (1 to 2 mL) to one tube and 0.1 M iron (III) chloride solution (1 to 2 mL) was added to the other. Observation was recorded. Part B : Copper(II) sulfate solution with ammonia 2 mL of 0.1 M copeer(II) sulfate was placed into each of two test tubes. 1. Test tube 1 : For colour comparison. 2. Test Tube 2 : 6 M NH3(aq) or NH