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E-9
3.
In which direction does the oxalic acid dissociation equilibrium (equation (7)) shift when H3O
+
(aq)
is
added to a 0.10 M solution of oxalic acid (H2C2O
4
)?   Why?
Answer:  Reaction shifts to the left, restoring K' by increasing  [H2C2O
4
] and decreasing [H3O
+
] and
[C2O
4
2-
] .
4.
Predict what happens to the position of equilibrium when OH
-
(aq)
is added to a solution containing a
Fe
3+
(aq),
NCS
-
(aq)
and
[Fe(NCS)]
2+
(aq)
at equlibrium (equation (8))?  Why?
Answer:  
The added OH
-
(aq)
will react with the Fe
3+
(aq)
causing the [Fe
3+
] to decrease. The
[Fe(NCS)]
2+
(aq)
equilibrium (equation 8) will shift to the left, restoring K by replacing the
[Fe
3+
] that reacted with the OH
-
(aq)
.  This shift will result in a decrease in the concentration of
[Fe(NCS)]
2+
(aq)
causing the colour intensity of the solution to lighten.
5.
An acidic solution, containing approximately equal concentrations of [CoCl
4
]²
-
(aq)
and 
[Co(H2O)
6
]
2+
(aq)
in equilibrium was studied (equation (11)).  This solution changed from violet to pink
when cooled.  Use Le Châtelier's Principle to determine if this reaction is endothermic or exothermic. 
6.
Calculate the initial concentrations of copper(II) nitrate and sodium hydroxide, if 2.0 mL of 
0.50 M Cu(NO3)2 was combined in a test tube with 5.0 mL of 6.0 M NaOH.  
Answer:  Cu(NO3)2 is 0.14 M and NaOH is 4.3 M
REAGENTS
0.050 M Fe(NO3)3 (iron(III) nitrate)
0.020 M KNCS  (potassium thiocyanate)
6.0 M NaOH  (sodium hydroxide)
0.20 M Na2C2O
4
  (sodium oxalate) 
0.20 M NaF  (sodium floride)
0.10 M K
4
[Fe(CN)
6
]  (potassium hexacyanoferrate(II))
1.0 M NH3  (ammonia) 
0.10 M AgNO3  (silver nitrate)
1.0 M Pb(NO3)2   (lead(II) nitrate)
1.0 M NaCl  (sodium chloride)
0.50 M Na2CrO
4
  (sodium chromate)
1.0 M Na2S  (sodium sulfide)
12.4 M HCl  (hydrochloric acid)
1.0 M HCl  (hydrochloric acid)
[CoCl
4
]²
-
/ [Co(H2O)
6
]
2+
equilibrium solution (cobalt(II) complex ions) 
ice
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