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| Properties of Hydrogen |
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 Hydrogen is a colourless, odourless and tasteless gas. Impure hydrogen has a fishy smell due to its impurities ,arsine and phosphine. |
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Hydrogen is the lightest element. It is by far the most abundant element in the universe and makes up about 90% of the universe by weight. Hydrogen as water (H2O) is absolutely essential to life and it is present in all organic compounds. |
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Hydrogen gas was used in lighter-than-air balloons for transport. |
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It is insoluble in water and a difficult gas to liquefy. |
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Hydrogen is a combustible gas, but does not support combustion. In presence of air or oxygen it burns with a blue flame to form water. If hydrogen is mixed with oxygen, it explodes with a pop sound. |
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| A Jet of Hydrogen Burns in Air with a Pale-blue Flame. |
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| The Steam is Condensed to Water on a Cold Surface |
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It is neutral towards litmus. |
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Hydrogen reacts with many non-metals. It combines with nitrogen in the presence of a catalyst to form ammonia, with sulphur to form hydrogen sulphide, with chlorine to form hydrogen chloride, and with oxygen to form water. |
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Hydrogen also combines with some metals, such as potassium and calcium, to form hydrides. |
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It acts as a reducing agent on metallic oxides, such as copper oxide, removing the oxygen and leaving the metal in a free state. |
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Hydrogen reacts with unsaturated organic compounds sparked by carbon electrodes to form corresponding saturated compounds. |
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