Hydrogen

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Symbol: H Formula: H2 Valency: 1 Atomic number: 1 Atomic mass: 1.00794 amu Hydrogen is the lightest element and exists as diatomic molecules.

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Hydrogen is placed in the reactivity series because many of its chemical reactions are similar to those of metals. Reactivity series order: K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Hg, Ag, Au, Pt.

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Robert Boyle first prepared hydrogen gas in 1672. Henry Cavendish studied it in 1776 and called it inflammable gas because it burns easily. Lavoisier named it hydrogen in 1783, meaning water producer.

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Balanced equation: 2 H2O --Electric--> 2 H2 + O2 Hydrogen is collected at the cathode and oxygen at the anode. The gases are formed in a 2:1 ratio by volume.

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Addition of acid to water makes it a good conductor of electricity. This helps electric current pass through the solution and causes decomposition of water into hydrogen and oxygen.

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General equation: Metal + Dilute acid → Salt + Hydrogen This is a common method of preparing hydrogen in the laboratory.

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Zn + 2HCl → ZnCl2 + H2(g) Granulated zinc is used in the lab preparation of hydrogen.

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Zn + H2SO4 → ZnSO4 + H2(g) This reaction liberates hydrogen gas in the laboratory.