Reaction of Metals with Sulfuric Acid

Problem Diluted acids can dissolve base metals and produce hydrogen and a salt solution. In the case of the reaction of magnesium with dilute sulfuric acid, hydrogen and magnesium sulfate solution are produced. Concentrated acids dissolve a metal too however no hydrogen is formed. In the reaction of concentrated sulfuric acid with zinc, the gas hydrogen sulfide is produced which has a rotten-egg smell. It is therefore important, in the case of sulfuric acid to differentiate between the pure acid from the diluted acidic solution and should be labeled carefully. Both reactions are not acid-base reactions - they are redox reactions (see Chap. 8). 

Material Test tubes, burner magnesium ribbon, zinc powder, concentrated sulfuric acid, about 2 M sulfuric acid solution. 

Procedure (a) Fill a test tube to one-third with sulfuric acid solution, add a 5-cm length of magnesium ribbon, and place an empty test tube of the same size 

Observation (a) A lively bubbling development of gas begins, the solution in the test tube gets hot, the piece of magnesium decreases in size and is completely dissolved. The gas in the second test tube reacts near the flame with a special pop sound hydrogen. Crystals of white salt crystallize from the solution after the evaporation of the water magnesium sulfate, (b) A small amount of gas can be observed, the gas has a peculiar smell hydrogen sulfide. 

Tip Because both reactions are classic redox reactions, they should not be interpreted within the chapter acids and bases - the phenomena should merely be demonstrated. The theme redox reactions picks up on both reactions again (see Chap. 8). 

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