Chemistry Reference
In-Depth Information
Material: 3 gas syringes with tap, test tubes, fitting rubber stoppers with fitting hole;
sodium hydroxide pearls (C), oxygen, nitrogen, carbon dioxide.
Procedure: The gas syringes are to be filled with one of the stated gases to the
100 mL-mark, closed and connected to the rubber stopper. The three test tubes are
to be filled with 10 sodium hydroxide pellets each. One after the other is to be
overlayed with one of the mentioned gases: therefore first the gas syringe is to be
put loosely on the test tube, the air is to be pushed out of the test tube by the gas until
50 mL remain in the syringe (see figure in E5.13). Then the syringe is to be locked
gas-tight to the test tube. The gas volume is to be observed on all three gas syringes
for a couple of minutes.
Observation: Neither the oxygen volume nor the nitrogen volume changes, but the
carbon dioxide volume decreases: in this case small white crystals form on the
sodium hydroxide pellets.
E5.13: Reaction of Sodium Hydroxide Solution with Carbon Dioxide
Problem: From E5.12 the observer concludes that sodium hydroxide reacts with
carbon dioxide. They know that water dissolves the gas carbon dioxide - for
example in mineral water. The solution of sodium hydroxide should also dissolve
the stated gas. The hypothesis may be: sodium hydroxide solution reacts with the
gaseous carbon dioxide.
The hypothesis should also include the concentrations of sodium hydroxide
solutions: concentrated sodium hydroxide solution dissolves carbon dioxide better
than a diluted solution. Again, the students can independently construct an appara-
tus that verifies the hypothesis. The test series described in E5.12 is one possibility.
Material: 3 gas syringes with tap, test tubes, rubber stoppers with fitting hole; conc.
sodium hydroxide solution (approx. 10-M), carbon dioxide.
