Video Transcript
Which of the following statements is correct? (A) Iron can be dissolved in diluted hydrochloric acid, producing iron(III) chloride and hydrogen gas. (B) Iron can be dissolved in diluted hydrochloric acid, producing iron(III) chloride and water. (C) Iron can be dissolved in diluted hydrochloric acid, producing iron(II) chloride and water. Or (D) iron can be dissolved in diluted hydrochloric acid, producing iron(II) chloride and hydrogen gas.
This question is asking about a specific reaction between iron and diluted hydrochloric acid. A more general description of this reaction is that it involves a metal and a dilute acid. The second half of each answer choice lists the possible product of this reaction. The reaction will produce either iron(III) chloride or iron(II) chloride and either hydrogen gas or water. Thankfully, there is a pattern to this kind of reaction that we can use to narrow down our answers. When a metal reacts with a dilute acid, the products are a salt and hydrogen gas. While we don’t yet know whether the salt in this case is iron(II) chloride or iron(III) chloride, we can say that the second product is hydrogen gas and not water.
Since choice (B) and choice (C) are incorrect, let’s erase them to give ourselves more room to work with. The chemical equation is beginning to take shape. Iron plus hydrochloric acid produces some form of salt and hydrogen gas. Is the unknown salt iron(II) chloride or iron(III) chloride? To fill in this missing piece of information, we can remember a rule. Dilute acids produce Fe2+ ions in the presence of iron. It takes a more concentrated acid to remove an extra electron from iron to produce a three plus ion. An Fe2+ ion, or in other words an iron(II) ion, combines with two chloride ions to make the compound iron(II) chloride.
To balance this equation, we will show that two moles of hydrochloric acid will react with each one mole of iron in the reactants. So we can say that the products of this reaction are iron(II) chloride and hydrogen gas, the products indicated by answer choice (D). So which of the following statements is correct? That’s choice (D): Iron can be dissolved in diluted hydrochloric acid, producing iron(II) chloride and hydrogen gas.
