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of ferric hydroxide sol from the burette in four clean test tubes, add the neces-
sary volume of water. Then add the necessary volume of electrolyte to each tube
and mix it immediately. After 10 minutes, note which turbidity is observed in
the test tubes. Record the results of the observations in the table («+» or «-»).
Calculate the coagulation threshold of the sol and the coagulability for each
electrolyte, using the equation:
1000
el
el
Th
sol
el
С V
С
V V
⋅
=
⋅
+
where C
el
is the normality of electrolyte, mol/l; V
el
is the smallest volume of
the initial electrolyte solution, which causes coagulation of a given volume of
sol, l; V
sol
is the volume of the sol, l.
Record the results of calculations in the table. Indicate coagulating ions. Is
the Schulze-Gardi rule observed?
№ tube
Volumeof… Results of observations Results of calculations
sol water electrolyte
electrolytes
С
ct
(ммоль/л)
coagulability
(л/ммоль)
KCl
K
4
[Fe (CN)
6
]
1
0,5 4,5
0,5
2
1 4
1
3
2 3
2
4
4 1
4
Experiment 6. Investigation of the phenomenon of protection of sols
.
Add 0.0025 M solution of Na
2
SO
4
from the burette to 10 ml of iron hydroxide
sol until the turbidity in the solution appears. Add 1 ml of a 0.5% gelatin
solution to 10 ml of Fe (OH)
3
sol solutionin another flask. Stir and add as much
Na
2
SO
4
solution as required for coagulation in the first flask. What happens in
the flask? Add as much electrolyte as is added already. Did coagulation occur?
Explain the protective effect of gelatin.
LESSON 14.
FINAL CONTROL № 2
Final control № 2 contain the following topics:
1. Complex compounds
2. Chemistry of biogenic elements
3. Electrode and redox potentials.
4. Superficial phenomena. Adsorption.
5. Colloidal solutions and their properties. Theory of coagulation.