Question

ASAP FOR ALL QUESTIONS ABOUT THE Le Chatelier’s Principle LAB

Procedure :

I ) NaCl (s)   ßà   Na+ (aq)   + Cl- (aq)

         *Add few drops of conc. HCl to 2 to 3 mL of saturated NaCl solution.

II ) NH4Cl(s) ßà NH4+ (aq) + Cl-(aq)

         *Add few drops of conc. HCl to 2 to 3 mL of saturated NH4Cl solution.

III ) Fe+3(aq) + SCN-(aq) ßà Fe(SCN)+2(aq)

         Prepare a stock solution by mixing 2mL each of 0.1M FeCl3 and 0.1M KSCN in 100mL graduated cylinder. Add enough water to make 100mL solution. Note the color. If you are the first one to use this station, make this solution and save it for the rest of the class. If you are using someone else’s stock solution, make sure to make observations of each reactant.

(4) *Add about 1mL of 0.1M FeCl3 to about 5mL of stock solution.

(5) *Add about 1mL of 0.1M KSCN to about 5mL of stock solution.

(6) *Add 0.1M AgNO3 DROPWISE (less than 1mL) to about 5mL of stock solution until almost all the color is discharges. (The white ppt is a mixture of AgCl and AgSCN.) Split the solution into two test tubes including the precipitate.

(6a) Add 0.1M KSCN dropwise (about 2mL) to one tube

(6b) Add 0.1M FeCl3 dropwise (about 2mL) to the other tube.

IV) 2CrO4 –2(aq)    +   2H+ (aq)   ßà Cr2O7 –2(aq)    +    H2O(l)

         *Add 2 drops of 6M HNO3 to about 3mL of 0.1M K2CrO4.

Add 10% NaOH to (7) dropwise until the original color of K2CrO4 is restored.

(9) *Add 2 drops of 6M H2SO4 to about 3mL of 0.1M K2CrO4.

(10) Add 10% NaOH to (9) dropwise until the original color of K2CrO4 is restored.

V) Co(H2O)6 +2(aq)   + 4Cl-(aq)   ßà CoCl4 –2(aq) + 6 H2O

         *Add about 3mL of Conc. HCl solution dropwise to about 2mL (no more than) of 0.1M CoCl2.

         Add water to (11) until the reverse reaction is evident.

VI) NH3(g)   + H2O(l) ßà NH4+ (aq)   + OH-(aq)

         Prepare a stock solution by mixing 4 drops of conc. NH4OH and 3 drops of phenolphthalein in 100mL graduated cylinder. Add enough water to make 100mL solution. Note the color. If you are the first one to use this station, make this solution and save it for the rest of the class. If you are using someone else’s stock solution, make sure to make observations of each reactant.

(14) *Dissolve a very small amount of solid NH4Cl in about 5mL of stock solution.

(15) *Add a few drops of 6M HCl to about 5mL stock solution.

Questions :

(Q1) In step (1), which direction DID the equilibrium shift? What was the visual indication of the shift?

(Q2) In step (5), which direction DID the equilibrium shift? What was the visual indication of the shift?

(Q3) In step (7), which direction DID the equilibrium shift? What was the visual indication of the shift?

(Q4) Write a balanced net ionic equation showing what happened in step (6).  

(Q5) In step (6a), what is the stress and which direction DID the equilibrium shift? What was the visual indication of the shift? Use the equation from Q4.

(Q6) In step (10) , which direction DID the equilibrium shift? Using balanced equations, explain the direction of this shift.

Answer 1

Q1: Adding HCl promotes the movility of the Cl ions, so equilibrium will shift to the products.

Q2: Adding more KSCN, raises concentration of KSCN so, equilibrium will shift to the reactants.

Q3: Adding more base, will cause that the concentration of CrO4 increases and the H+ decreases, so the equilibrium will shift to the products. the dissapearence of the original color is the evidence of the shift.

Q4: Original equation:

FeCl_3(aq)+ KSCN_(aq) ----------> FeSCNCl_2(aq)

Adding AgNO₃:

Fe³⁺_(aq) + 3Cl^-_(aq) + K⁺_(aq) + SCN^-_(aq) + 2Ag⁺_(aq) + 2NO₃^-_(aq) -----------> Fe³⁺_(aq) + SCN^-_(aq) + K⁺ + 2Cl^- + AgCl_(s) + AgSCN_(s) + 2NO₃^-

The net equation would be:

Cl^-_(aq)+ SCN^-_(aq) + 2Ag⁺_(aq) -----------> AgCl_(s) + AgSCN_(s)

Q5. Adding KSCN will increase concentration of SCN so reaction will shitf to the left (reactants)

Hope this helps