What happens when calcium is treated with cold water?

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Detailed Solution

Calcium reacts moderately with cold water to form calcium hydroxide and hydrogen gas: Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g). The reaction is less vigorous than alkali metals but faster than magnesium. Bubbles of H₂ adhere to the metal, and the solution becomes alkaline due to slightly soluble Ca(OH)₂ (“lime water”). The heat evolved is insufficient to ignite hydrogen in cold water.

As temperature increases, solubility of Ca(OH)₂ rises and the reaction appears faster. This pattern fits the Group 2 trend: reactivity increases from Mg < Ca < Sr < Ba. Indicators like phenolphthalein turn pink, confirming alkali formation. Net effects: effervescence, formation of a milky alkaline solution, and gradual consumption of the metal.

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