Reaction

Metal + dilute hydrochloric acid ➡️ metal chloride + hydrogen

Metal + dilute sulphuric acid ➡️ metal sulphate + hydrogen

钾钠（explosive reaction）钙镁铝锌铁（react more slowly）铅（very slow reaction）铜汞银铂金（no reaction）

Reactivity

  Reactivities of elements decrease across a period and increase down a group.

Conserving and Protecting Metals

  Metals ores in the Earth's crust are limited in amount and non-renewable, so it's necessary to conserve metals. Below are 3 common ways (3 'R's):

1. Reusing metal articles

2. Reducing the use of metals

3. Recycling used metals

  All metals look shiny when they are freshly cut but become dull when exposed to air (since metals reacts with oxygen and water in the air), so it is essential to store metals with relative methods and take action to protect them from rusting.

铁生锈（被腐蚀）

  The appearance of acidic pollutants, the presence of soluble ionic compounds, the higher temperature and the attachment of less reactive metals can make metals corrode more quickly. Besides, scratched, bent or sharp areas of the metal object rust faster.

Insulating Metals

  To prevent reaction with air, very reactive metals (K, Na) are stored under paraffin oil, and quite reactive metals (Ca) are kept in airtight containers. Gold is the least reactive of all metals - it does not react with oxygen and water, so it needs no special method of storage.

  A protective layer is used to protect the using metals. The layer can be made by other materials that don't react with the air, such as paint and plastic. However, the moving parts of machines and woodworking tools are not painted or coated with plastic, because they would be scratched off easily, so aforementioned metal tools use oil or grease instead. Besides, coating a metal with another [[metal like zinc or tin also works. Electroplating can also coat a metal with another metal.

electroplating iron

Cathodic Protection

iron being protected by cathodic protection

  Cathodic protection can provide metal with electrons, what they lose when rusting.

Sacrificial Protection

  Since a metal give electron to be rusted, when making it contacting a metal that is more readily to give electrons, that is, more reactive, the original metal can be protected by sacrificing the other one.

Using Alloys

  Stainless steel is an alloy of iron, produced by mixing iron with carbon and other metals such as chromium. Chromium form a tough and protective chromium(III) oxide layer on the surface. Aluminum is protected in a similar way, as it reacts with oxygen easily and form a tough aluminum oxide layer.

Experiment set-up for thickening aluminum oxide layer

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Displacement Reactions of Metals