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Color Changes in Thiocyanate Iron Equilibrium System

This lesson discusses the color changes observed when Fe(NO3)3, KSCN, and NaOH are added to the thiocyanate iron equilibrium system. The equilibrium equation is Fe3+(aq) + SCN-(aq) ⇄ Fe(SCN)2+(aq), where Fe(SCN)2+ is yellow-brown. Adding Fe(NO3)3 and KSCN increases their respective concentrations and causes the reaction to shift right and turn brown. Adding NaOH increases [OH-], reacts with Fe3+ to lower its concentration, and turns the solution yellow, shifting the equilibrium left.

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Color Changes in Thiocyanate Iron Equilibrium System

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  1. Lab Le Chatelier's Principle Lesson 4

  2. Part I + Thymol Blue (blue) + H+ ⇌ Thymol Blue (yellow) OH- HOH  Na+ + OH- Add NaOH Add HCl  H+ + Cl- spectator stress stress spectator OH- lowers H+ Right yellow left blue

  3. Part II yellow orange Energy + 2CrO42- + 2H+ ⇌ Cr2O72- + H2O(l) + + Ba2+ OH- ⇌ ⇌ HOH BaCrO4(s)

  4. Part III yellowbrown Fe3+(aq) + SCN-(aq)⇌ FeSCN2+(aq) + 3OH- ⇌ Fe(OH)3(s)

  5. Part IV Co(H2O)62+ + 2Cl- ⇌Co(H2O)4Cl22- + 2H2O(l) pinkblue

  6. Part V light blue powder blue ppt Cu(H2O)42+ + 2NH3 ⇌ Cu(OH)2(s) + 2NH4+ + 2H2O + + 4NH3 H+ ⇌ ⇌ Cu(NH3)42+ violet NH4+ + 2OH-

  7. Energy + 2CrO42- + 2H+ ⇄ Cr2O72- + H2O(l) yellow orange AcidisH+ Base is OH- Acids react with bases H+ + OH-→ H2O(l) Stress Shift Add HCl right Add K2CrO4 right Add K2Cr2O7 left

  8. yelloworange 2CrO42- 2H+ Energy + + ⇄ Cr2O72- + H2O(l) + + Ba2+ OH- ⇌ ⇌ BaCrO4(s) HOH shifts right- all CrO42-changestoCr2O72- HCl 5 drops 6 M (lots!) Ba(NO3)2 noCrO42- -no reaction left- makes CrO42- NaOH yellow ppt

  9. 1. Explain the colour changes observed when Fe(NO3)3, KSCN, and NaOH were added to the thiocyanairon equilibrium system. Start by writing the equilibrium equation. Fe3+(aq) + SCN-(aq)⇄ Fe(SCN)2+(aq) yellow brown Adding Fe(NO3)3 increasesthe [Fe3+] and causes the reaction to shift right and turn brown. Adding KSCN increases the [SCN-] and causes the reaction to shift right and turn brown. Adding NaOH increasesthe [OH-] ,which reacts with Fe3+ , lowering the [Fe3+], , and turn yellow. causing the equilibrium to shift left

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