Which ion would magnesium make

Institute Dr. Flad
Vocational college for chemistry, pharmacy, biotechnology and the environment

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Reaction of magnesium with dilute hydrochloric acid

Kristian Helmis, Thomas Bäuml and Markus Zehender (LG47)


1. Aim of the experiment:

This experiment is intended to demonstrate the reaction of base metals with dilute, non-oxidizing acids as an example. On the one hand, it can be shown that a base metal (here: magnesium) is able to release hydrogen from an acid; on the other hand, the oxyhydrogen sample is shown as qualitative evidence for hydrogen (more precisely: for a mixture of hydrogen and air or oxygen) .


2. Theoretical principles / reaction equations:

The standard potential E0 of the redox system Mg Mg2+ + 2 e- is -2.363 V. Magnesium is therefore to the left of the redox system H in the voltage series2 + 2 H.2O 2 H3O+ + 2 e-. As a base metal, it can release elemental hydrogen from an aqueous system. The equation for this is (as a gross equation):

Mg + 2H3O+ Mg2+ + H2 + 2 H.2O

The hydrogen can be collected in different ways. If you mix it with air (or pure oxygen) to form an oxyhydrogen gas mixture, this mixture can be ignited and the characteristic bang of an explosive hydrogen combustion can be heard. The combustion takes place according to the following equation:

2 H2 + O2 2 H2O


3. Chemicals:

1 piece of magnesium tape (blank), approx. 3 cm long
1-2 ml dil. Hydrochloric acid (c = 2 mol / l)
20-30 ml soap solution (not too diluted)


4. Construction:


5. Implementation:

The piece of magnesium tape that has been scuffed with sandpaper is placed in the test tube, the test tube is screwed on and attached to the plate with the pins. Make sure that the side of the test tube, which is bent downwards, is immersed in the beaker with the soap solution. The soap solution can be obtained by filling the beaker approximately 2/3 with water and adding the amount of soap that is obtained by pulling the soap dispenser once (on toilets). The soap must be evenly distributed in the solution. It is important to ensure that the beaker stands securely on the test tube stand. A lifting platform can also be used instead of the RG stand. 1-2 ml of dilute HCl are drawn into the syringe and the cannula is pierced through the septum. Approx. 1 ml of HCl is now injected into the RG. You will immediately observe a gas evolution in the RG, which lasts for a very long time. When it gets weaker, add more HCl. The resulting gas will soon reach the soap solution and form bubbles there. The first bubbles come from the displaced air, but after about half a minute enough hydrogen has formed to be able to carry out the detonating gas test. The use of a match is recommended. If you approach the bubbles with the flame, you will, depending on the amount of gas produced, observe a more or less violent bang combined with a short, violent flash. Since the gas development i.a. If done very quickly, you can possibly carry out 3 oxyhydrogen gas samples in quick succession.