Chemistry Reference
In-Depth Information
a 1-M sodium hydroxide-standard solution is to be presented with pH-value 14. This
solution is to be dilutedwith the factors 1:10, 1:100, and 1:1,000. The pH-values 13, 12
and 11 will be measured. Now it is clear that the pH-value changes by one, when the
concentration of the solution varies by factor 10. The concentration of OH
(aq) ions,
which matches the metered pH-value of E5.14, can be estimated by this test series.
Material: pH-meter, 3 measuring cylinders (100 mL), transferring pipette (10 mL);
special indicator paper (for the estimation of pH-values in the range of 11-14),
sodium hydroxide solution (
c
1 mol/L).
Procedure: The sodium hydroxide-standard solution is to be tested with the indica-
tor paper. 10 mL of the standard solution are to be poured into the first measuring
cylinder, diluted to exactly 100 mL and well mixed by shaking. This solution is to
be diluted again by 1:10 and the new solution is to be diluted once more by 1:10. All
solutions are to be tested with pH-meter and indicator paper, pH-values and
concentrations are to be compared.
Observations: The pH-values are 14, 13, 12, and 11. The pH-values change by one
unit, when the solution is diluted by 1:10.
ΒΌ
E5.16: Model Experiment Demonstrating the Mercury Electrode Process
Problem: The mercury electrode process is used industrially to obtain pure chlo-
ride-free sodium hydroxide solution through the electrolysis of cheap rock salt
solution. Sodium amalgam is formed during the electrolysis and decomposed again
by adding water. Formation and decomposition of sodium amalgam can be
simulated in a model experiment - in this case an experiment functions as a model.
Material: Transformer, iron and graphite electrode, cables and alligator clips, U-tube,
glass tube, spill tray; mercury (T), sodium chloride, phenolphthalein solution.
10 V
iron
electrode
graphite
electrode
glass tube
CI
2
(g)
phenol-
phthalein
solution
NaCI (aq)
Hg (l)
Procedure: Mercury is to be poured into the U-tube (fixed above the spill tray). The
iron electrode in the glass tube is to be installed in one leg as a minus pole, water
laced with phenolphthalein is to be added. The other leg is to be filled with
