Which of the following equations correctly represents the reaction between aluminum and dilute hydrochloric acid to produce aluminum chloride and hydrogen gas?
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Correct answer
A. 2Al + 6HCl → 2AlCl3 + 3H2
Principle or equation
Balanced chemical equations must have equal numbers of each type of atom on both sides. Aluminum reacts with hydrochloric acid to form aluminum chloride (AlCl3) and hydrogen gas (H2).
Why this answer is correct
Aluminum has a +3 oxidation state, so it forms AlCl3. The unbalanced equation is Al + HCl → AlCl3 + H2. To balance: place coefficient 2 before Al and AlCl3, coefficient 6 before HCl, and coefficient 3 before H2. Check: 2 Al, 6 H, 6 Cl on both sides.
Example
For the reaction of sodium with water: 2Na + 2H2O → 2NaOH + H2. Balancing ensures atom conservation.
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