1. Lab
Le Chatelier's
Principle
Lesson 4

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

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

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

5. Part IV
Co(H2O) Cl- ⇌ Co(H2O)4Cl H2O(l)
pink blue

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

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

8. yellow orange
Energy ⇄ Cr2O H2O(l)
2CrO42-
2H+ +
Ba2+ +
BaCrO4(s) ⇌
OH- ⇌
HOH
HCl 5 drops 6 M (lots!)
shifts right- all CrO42- changes to Cr2O72-
Ba(NO3)2
no CrO42- -no reaction
NaOH
left- makes CrO42-
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
increases the [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
increases the [OH-]
,which reacts with Fe3+
, lowering the [Fe3+],
causing the equilibrium to shift left
, and turn yellow.