Task 3. Chemical properties of metals

A) Reaction of metals with hydrochloric acid

The teacher prepares a pair of rubber gloves, a pair of protective glasses, and a lab coat for each student. For each working group, the teacher prepares a test tube stand, 8 test tubes, emery paper, a dropper, 10% solution of hydrochloric acid, metals – zinc, iron, copper and aluminium, copper covered by patina and iron covered by rust.

Pupils put on the coats, protective glasses and rubber gloves. They prepare 4 test tubes in the stand and number them 1 to 4. Pupils work with metals, which are covered by a layer of their oxides. Pupils put a piece of zinc into the first test tube, a piece of iron into the second, a piece of copper into the third and a piece of aluminium into the fourth.

Pupils add 10% solution of hydrochloric acid to each sample of metals by a dropper. Pupils first make a presumption about the process of the chemical reaction. Consequently, they carry out the experiment and write down their observation in the prepared table.

Pupils prepare another four test tubes in the stand and number them 5 to 8. They thoroughly clean the pieces of metals by emery paper – copper covered by the patina must have red-brown colouring. Aluminium, which is covered by aluminium oxide, must be cleaned until it gets a metallic sheen. Rusty corrosion must be removed from iron, it will then have a metallic sheen colour and so will zinc after the cleaning.

Pupils put a piece of cleaned zinc in the test tube number 5, a piece of iron in the test tube number 6, a piece of copper in the test tube number 7 and a piece of aluminium in the test tube number 8. Pupils add 10% solution of hydrochloric acid to each sample of metals by a dropper. Pupils first make a presumption about the process of the chemical reaction and consequently they carry out the experiment and write down their observation in the prepared table.

B) Effects of long-range interaction of aqueous solutions on metals

The teacher, at least one week before the planned laboratory practical, prepares samples of metals in various environments into 8 test tubes. He/she thoroughly cleans the metals with the emery paper. The teacher places first 4 test tubes in the first laboratory stand and fills them with tap water. He/she puts zinc in the first test tube, iron into the second one, copper into the third one and aluminium into the fourth one.

The teacher places another 4 test tubes in the second laboratory stand, fills them with vinegar and puts in the same four metals. He/she puts zinc in the fifth test tube with vinegar, iron into the sixth one, copper into the seventh one and aluminium into the eighth one.

The samples of metals must be immersed in the water and vinegar at least by two thirds. The teacher labels the test tubes and closes them by a ball of cotton wool so that the gas that is being released can freely leak. After that, the teacher leaves the test tubes to stand on the same place until the laboratory practical.

The teacher encourages pupils to predict, based on the carried out experiments and their own experience, what will happen to the metals, which have been placed in the water and vinegar for a week. After pupils have written down their expectations in the worksheet, the teacher will show them the test tubes with the metals, which were exposed to long-term effects of water and vinegar.