Transcript Document

Lab
Le Chatelier's
Principle
Lesson 4
Part I
Thymol Blue (blue)
+
H+
⇌
Thymol Blue (yellow)
+
OH-
HOH
Add HCl
Right
 H+ + Clstress spectator
yellow
 Na+ + OHspectator stress
lowers H+
left
blue
Add NaOH
OH-
Part II
yellow
Energy
+ 2CrO42-
orange
+ 2H+
+
+
Ba2+
OH-
⇌
⇌
BaCrO4(s)
HOH
⇌ Cr2O72-
+
H2O(l)
Part III
yellow
Fe3+(aq)
+
3OH-
⇌
Fe(OH)3(s)
brown
+ SCN-(aq)
⇌
FeSCN2+(aq)
Part IV
Co(H2O)62+ + 2Cl- ⇌ Co(H2O)4Cl22- +
pink
blue
2H2O(l)
Part V
light blue
powder blue ppt
Cu(H2O)42+ + 2NH3 ⇌
+
H+
Cu(OH)2(s) +
2NH4+
+
4NH3
⇌
⇌
NH4+
Cu(NH3)42+ violet
+
2OH-
+ 2H2O
Energy
+
2CrO42- + 2H+
yellow
⇄
Cr2O72- +
orange
Acid is H+
Base is OHAcids react with bases
H+ + OH- → H2O(l)
Stress
Shift
Add HCl
right
Add K2CrO4
right
Add K2Cr2O7
left
H2O(l)
yellow
Energy
2CrO42-
+
2H+
+
+
Ba2+
OH-
⇌
⇌
HCl
+
orange
BaCrO4(s)
HOH
5 drops 6 M (lots!)
⇄
Cr2O72- + H2O(l)
shifts right- all CrO42- changes to Cr2O72-
Ba(NO3)2
no CrO42- -no reaction
NaOH
left- makes CrO42yellow ppt
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.