CHE 169 Le Chatelier\'s Principle and Chemical Equilibrium Exp. #4 Run each of t
ID: 1026626 • Letter: C
Question
CHE 169 Le Chatelier's Principle and Chemical Equilibrium Exp. #4 Run each of the following reactions in test tubes. 1·Label a test tube #1, and add a few mL of NaOH to it. mi cape Add CaCl2 drop wise until a noticeable precipitate of Ca(OH)2 is present. "3.Now add a few drops of the pheno phth le indicator to the test tube #1 with the CaQH)2 in it. %,Add 6M HCl (NOT 12MI!!) drop wise to the first test tube (#1) with the Ca(OH)2 until a change is observed. Record your results. 5. Prepare a stock solution by mixing 2mL of 0.1M FeCls and 0.1M KSCN in a 4ee-mL graduated yinder adding H20 to bring the volume to 100 mL. Save this stock solution for the rest of the class. on wa Irnl 6-Take 5mL of the stock solution and note the color. Add about 1mL of 0.1M Fe tion and observe the result. Take 5mL of the stock solution and note the color. Add about 1mL of 0.1M KSCN solution and observe the result. 8. Take 5mL of the stock solution and note the color. Add 0.1M AgNOs solution drop wise until almost all the color is gone. ' Add 2 drops of 6M HNOs to roughly 3mL of 0.1M K2CrO4 solution and observe the result "AdAdd 10% NaOH solution dropwise to the solution from step 9 until the original color is tored d 3 mL of conc. HCI dropwise to 2mL (no more) of 0.1M CoCl2 and observe the e Result 12:Add water dropwise to the solution from step 1 1 until the reverse reaction is evident. 13Take the test tube from step 12 and place it in a water bath on a Bunsen burner and hea 14. Label a test tube #3, and then add afew mL of the Cua solution to it. 5 Add 6 M NaOH drop wise until a precipitate of Cu(OH)2 is observed. 16 Add 6M NH3 drop wise (Use Caution!! Are those goggles still on!) until a change is observed. You will probably need to stir or shake your test tube. Record your observations. 17. Add 6M HCl dropwise until a change is observed. Stir or shake as you add the HCl. Record all observations.Explanation / Answer
test tube #1)
1) changes taking place-
2NaOH(aq)+CaCl2(aq)---->Ca(OH)2 (s)+2NaCl(aq)
ionic eqn:
2OH- (aq)+ Ca2+(aq) <--->Ca(OH)2(s) The equilibrium shifted to right ,so that more product precipitate
(white )forms, as an excess of reactant Ca2+ or CaCl2 is added, to compensate for excess reactant Ca2+(Le chatlier's principle)
Add phenolpthalein to it, it is an indicator that is colorless in acidic medium ,but pink in basic medium.
With base Ca(OH)2,the color of solution appears pink,On adding HCl ,Ca(OH)2 neutralizes and at the end point ,(on adding little extra HCl(than that required for neutralization) ,the medium turns acidic as Ca(OH)2 is no longer present,the pink color fades away.
2HCl(aq) +Ca(OH)2 (s)<---->CaCl2(aq)+2H2O(l)
The product Ca(OH)2 concentration decreases ,so the equilibrium of the rxn ,shifts to the right again,to produce more product and compensate for the loss.(Le Chatlier's principle)
2OH- (aq)+ Ca2+(aq) <--->Ca(OH)2(s)