Lab 19-A
INVESTIGATING CHEMICAL EQUILIBRIUM
CHEM 12
Name:______________
OBJECTIVES:
1. To recognize the macroscopic properties of five chemical systems at equilibrium.
2. To observe shifts in equilibrium concentrations as stresses are applied to the systems.
3. To observe a shift in equilibrium concentrations associated with changes in temperature.
4. To explain the observations obtained by applying Le Chatelier’s principle.
Part 1 EQUILIBRIUM INVOLVING THYMOL BLUE
Thymol blue + H +  Thymol blue+
(blue)
(yellow)
Reagent added
Stress (ion added)
HCl (step 3)
HCl (step 4)
NaOH (step 5)
NaOH (step 6)
Color observation
Direction of eq. shift
Part 2 EQUILIBRIUM INVOLVING THIOCYANATOIRON (III) ION
Fe3+ + SCN−  FeSCN 2+
(light yellow)
(red)
Reagent added
KCl
Fe(NO3 )3
KSCN
NaOH
Stress (ion added)
Color observation
Direction of eq. shift
Part 3 EQUILIBRIUM INVOLVING COBALT (II) COMPLEXES
Co(H2 O)6 3+ (aq) + 2Cl− (aq)  Co(H2 O)4 Cl2 (aq) + 2H2 O(l)
(light red)
(dark red/purple)
Stress
Step 3
Step 4
Step 5
Step 6
Observation
Direction of eq. Shift
Part 4 EQIULIBRIUM INVOLVING CHROMATE AND DICHROMATE
2CrO4 2− (aq) + 2H + (aq)  Cr2 O7 2− (aq) + H2 O(l)
(yellow)
(orange)
Ba2+ (aq) + CrO4 2− (aq)  BaCrO4 (s)
Steps
2
And
3
Step
4
0.1M K 2 CrO4
0.1M K 2 Cr2 O7
0.1M K 2 CrO4
0.1M K 2 Cr2 O7
Initial color
1M NaOH added
1M HCl added
Initial color
1M HCl added
1M NaOH added
Steps 5
And 6
Steps 7
and 8
Initial color
+1M NaOH
+0.1M Ba(NO3 )2
+1M HCl
Initial color
+1M HCl
0.1M Ba(NO3 )2
+1M NaOH
0.1M K 2 CrO4
0.1M K 2 Cr2 O7
0.1M K 2 CrO4
Step 9
0.1M K 2 Cr2 O7
0.1M Ba(NO3 )2
Part 5 EQUILIBRIUM INVOLVING COPPER (II) COMPLEXES
NH3 (aq) + H2 O(l)  NH4 + (aq) + OH − (aq)
Cu2+ (aq) + 2OH−  Cu(OH)2 (s)
(blue)
Cu(H2 O)4 2+ (aq) + 4NH3  Cu(NH3 )4 2+ (aq) + 4H2 O(l)
(light blue)
(dark blue)
CuSO4
Appearance
3 drops NH3
More NH3
HCl added