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Most metals when placed in cold water undergo no observable changes and show no signs of a chemical reaction. However, some metals including lithium, potassium, sodium, and calcium do react with cold water to form hydrogen and a metal hydroxide.
For example, the reaction of sodium with water is very vigorous.
The formation of hydrogen in this reaction can be confirmed by collecting a sample of the gas produced and introducing a lighted splint. A small explosion or ‘pop’ confirms the presence of hydrogen gas. An acid-base indicator such as phenolphthalein or litmus can be used to confirm the production of hydroxide ions. Another group of somewhat less reactive metals including aluminum, zinc, and iron do not react with cold water but will react with steam to produce hydrogen and metal oxide.
Less reactive metals such as gold, silver, copper, platinum, and lead do not react with water or steam.

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