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Which of the following reaction is used to prepare dihydrogen gas in the laboratory?

  • A.\(2Fe_{(s)} + 3H_{2}O_{(l)} \underline{\Delta} \to Fe_{2}O_{3(s)} + 3H_{2(g)}\)
  • B.\(2Na_{(s)} + 2H_{2}O_{(l)} \to 2NaOH_{(aq)} + H_{2(g)}\)
  • C.\(Fe_{(s)} + 2HCl_{(aq)} \to FeCl_{2(aq)} + H_{2(g)}\)
  • D.\(Mg_{(s)} + 2H_{2}O_{(l)} \underline{\Delta} \to Mg(OH)_{2(s)} + H_{2(g)}\)
  • E.\(Ca_{(s)} + 2H_{2}O_{(l)} \to Ca(OH)_{2(aq)} + H_{2(g)}\)

Answer: C

The keyed reaction is \(Fe + 2HCl \to FeCl_{2} + H_{2}\).

In the laboratory, dihydrogen is prepared by the action of a dilute mineral acid on a reactive metal; granulated zinc with dilute HCl is the textbook choice, and iron with dilute HCl is the same kind of reaction. It runs at room temperature in simple apparatus and gives a steady stream of gas.

The other reactions are not laboratory methods: iron with steam and magnesium with hot water need heating; sodium with water is violently exothermic and dangerous; and calcium with water is less convenient and controlled than a metal-acid reaction.

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