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Experiment 9. Chemical Equilibrium and Equilibrium Shift.docx

Experiment 9. Chemical Equilibrium and Equilibrium Shift

Student Name (Print):______________________________
I. Objectives (1) Identify the change applied to an existing equilibrium; (2) Observe and explain the equilibrium shift direction upon the change applied.
II. Materials and Equipment
(1) Saturated NaCl aqueous solution; (2) 12 M HCl (concentrated solution); (3) 0.1 M K2CrO4 aqueous solution; (4) 6 M HNO3 aqueous solution; (5) 10% NaOH aqueous solution; (6) 0.05 M NH3 aqueous solution (freshly prepared); (7) phenolphthalein indicator solution; (8) 0.1 M CoCl2 aqueous solution; (9) solid NH4Cl		(10) small test tubes; (11) small test tube rack; (12) 250-ml beaker (2 ea); (13) scoopula; (14) small test tube clamp; (15) hot plate; (16) ice.
III. Safety Information and Requirements
(1) Wear goggles or safety glasses; (2) Dump waste according to waste container; (3) Be careful of using hot plate and hot water, and avoid finger burnt; (4) Be careful of concentrated acid/base solutions used in this lab. Immediately wash with plenty of water if any skin contact occurs. (5) Avoid breathing any chemical vapors.
IV. Principles, Procedures, and Practices
IV.1 Information of equilibrium and Le Chateliers Principle Chemical equilibrium is a status at which bother forward and backward reactions are proceeding with the same reaction rate. Thus, at the equilibrium, concentrations of reactants and products are constant unless the equilibrium is interrupted. The interruption of an existing equilibrium may be caused by the following changes: (1) Addition/removal of a reactant or a product; (2) Pressure/volume change (affecting only gas-involved equilibrium); (3) Increase/decrease of temperature. Based on Le Chateliers Principle, upon the interruption the equilibrium system will respond in the direction that will offset the change applied to the system.
IV.2 NaCl solubility equilibrium Information: In NaCl saturated solution, a solubility equilibrium is established. NaCls<=>NaClaq->Na+(aq)+Cl-aq
Procedure: (1) Add about 3 ml (about 1/3 of the small test tube volume) saturated NaCl solution into a small test tube. (2) Counting drop-by-drop, slowly and gently add 12 M HCl solution into the test tube until solid appears in the solution.		Observation and record: Any NCl solid in the solution? yes; no. Drops of HCl added before solid shows up:______ drops. Immediately upon the addition of HCl into the solution, which species concentration was increased? Na+; Cl-; NaCl(s). This change caused the equilibrium to shift in a direction of, from the right to the left; from the left to the right; no shift at all.
IV.3 Equilibrium between chromate and dichromate Information: Chromate (CrO42-) and dichromate (Cr2O72-) in aqueous solution have the following equilibrium. 2CrO42-aq+2H+aq<=>Cr2O72-aq+H2O(l) (yellow) (orange)
Procedure: (1) Get a clean small test tube. Add about 2 ml (about 1/5 of the test tube volume) 0.1 M K2CrO4 solution into the test tube. (2) Add about 2 ml 6M HNO3 solution into this test tube. (3) Now continue with adding 10% NaOH solution into this test tube until color change.	Observation and record: The solution color of K2CrO4 is __________________. The solution color now is __________________. Immediately upon the addition of HNO3 into the solution, which species concentration was increased? H+; CrO42--; Cr2O72-; H2O. This change caused the equilibrium to shift in a direction of, from the right to the left; from the left to the right; no shift at all. After color change, the solution color now is ___________________. Immediately upon the addition of NaOH into the solution, which species concentration was increased? H+; CrO42--; Cr2O72-; H2O. This change caused the equilibrium to shift in a direction of, from the right to the left; from the left to the right; no shift at all.
IV.3 Equilibrium of a weak base ionization Information: NH3(aq) is a weak based. It has the following ionization equilibrium in aqueous solution. NH3aq+H2Ol<=>NH4+aq+OH-(aq) With the presence of phenolphthalein, the solution displays pink color due to the high concentration of OH-.
Procedure: (1) Get a clean small test tube. Add about 3 ml (about 1/3 of the test tube volume) NH3 solution into the test tube. (2) Add one drop of phenolphthalein indication solution into the test tube (3) Add a medium scoopula of NH4Cl into the test tube and then gently shake to dissolve.	Observation and record: The solution color displays:______________ The solution color now is ___________________. Immediately upon the addition of NH4Cl into the solution, which species concentration was increased? H+; OH-; NH4+; H2O. This change caused the equilibrium to shift in a direction of, from the right to the left; from the left to the right; no shift at all.
IV.3 Equilibrium between cobalt complex ions Information: Co2+ in aqueous solution has the following complex ion equilibrium. CoH2O62+aq+4Cl-aq+heat<=>CoCl42+aq+4H2O(l) (red) (blue) In the forward direction, the reaction is a endothermic process.
Procedure: (1) Add half volume of tap water into a 250-ml beaker and put on a hot plate to heat till nearly boiling. (2) Add some ice into another 250-ml beaker and then add about half volume of tap water. (3) Get a clean small test tube. Add about 3 ml (about 1/3 volume of the small test tube) 0.1 CoCl2 solution into the test tube. (4) Add a medium scoopula of solid NH4Cl into this test tube. Gentle shake to dissolve. (5) Use a small test tube clamp to hold the test tube and put it in hot water in the beaker until a color change. Observe any color change of the solution in the test tube. (6) Now move the test tube from the hot water to the cold water in the beaker until a color change.		Observation and record: Solution color is:_______________. After the addition of NH4Cl, solution color is: ____________. What is the dominating Co compound in the solution? Co(H2O)62+; CoCl42+. The new color of the solution in the test tube is: __________. What is the dominating Co compound in the solution? Co(H2O)62+; CoCl42+. In the high temperature the equilibrium shifts in a direction of, from the right to the left; from the left to the right; no shift at all. The new color of the solution in the test tube is: __________. What is the dominating Co compound in the solution? Co(H2O)62+; CoCl42+. Is this equilibrium affected by temperature? yes; no. If you intend to have more CoCl42+ more than Co(H2O)62+ in the solution, you need to keep the solution in high or low temperature? low temperature; high temperature.