11-

E 111--------11111. Set-up

112.11 7 ml water + 7 mg Ca

113.11 Volumetric gas generation

11...............14. bTest for hydrogen1

Preparing a calcium sample, adding water, gas generation, combustion of the gas

Due to its shape and the high surface tension of water the no-cost ampoule can be totally filled with water, carefully turned upside down (Photo 2) and brought into contact with a solid that reacts with the water. If gases are produced they replace water inside the ampoule (Photos 3). The volume of it is equivalent to the mass of the solid reactant. The gas can be tested (Photo 4). By weighing the solid (Photo 1) and measuring the gas volume a quantititative relation will be explored.

Material
Tray, container for waste, goggles, 2 hammers, digital pocket scale (Diamond Series A04 or High-Precision Pocket Scale PS-20), gloves, ampoule 5 ml (high), syringe (5ml), permanent marker, sticky tape, aluminium beaker of a tea light, candle, scissors, grain of calcium, film canister.
Procedure
1. Transform the ampoule into a measuring container: Add water from a syringe in 1-ml-samples. Mark each of the water surfaces. Protect the graduation by sticky tape.
2. Photo 1: After treating a grain of calcium by a hammer, cut the disk into quarters and weigh them. (Attention: Wear gloves and keep the calcium dry!).
3. Photo 2: Transfer one quarter of the calcium disk into a beaker. Totally fill the ampoule with water. Carefully turn it upside down.
4. Photo 3: Place the ampoule full of water with its mouth on the calcium piece. Wait until the reaction is over. Measure the gas volume.
5. Photo 4 : Test the gas for hydrogen.
Observations
a) The calcium piece reacts with water releasing gas bubbles that replace 4.6 ml of water in the ampoule. A white precipitate is formed (Photo 3).
b) The gas has a smaller density than air. It burns without a bang ("negative Knallgasprobe" = negative oxyhydrogen test) (Photo 4).
Explanation
a) During the reaction Ca + 2 H2O --> H2 + Ca(OH)2 1 mmol (40 mg) of Ca release 1 mmol (24 ml) H2 at room temperature. So the expected volume released by 7 mg of Calcium is 4.2 ml.
b) The loudless combustion of the gas proves that it is hydrogen.
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first publication: 10.10.2008 l..l...last modification: 03.11.2008 l..l..l. back

pipette eudiometer to explode oxyhydrogen gas. second period: pipette experiments with 20 mg samples of calcium and calcium carbide. ..... 

 

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