Iron(II) sulfide reacts with hydrochloric acid according to the reaction: FeS(s) + 2 HCl(aq) → FeCl₂(s) + H₂S(g) A reaction mixture initially contains 0.223 mol FeS and 0.652 mol HCl. Once the reaction has occurred as completely as possible, what amount (in moles) of the excess reactant remains?

Verified step by step guidance

1. Step 1: Identify the limiting reactant. The stoichiometry of the reaction tells us that 1 mole of FeS reacts with 2 moles of HCl. So, for every mole of FeS, we need twice as many moles of HCl.
2. Step 2: Compare the amount of HCl needed for the reaction to the amount available. Multiply the moles of FeS by 2 to find out how many moles of HCl are needed. If this number is less than or equal to the amount of HCl available, then FeS is the limiting reactant. If it's more, then HCl is the limiting reactant.
3. Step 3: Calculate the amount of the excess reactant that remains after the reaction. If FeS is the limiting reactant, subtract the amount of HCl used (which is twice the amount of FeS) from the initial amount of HCl. If HCl is the limiting reactant, subtract the amount of FeS used (which is half the amount of HCl) from the initial amount of FeS.
4. Step 4: The result from step 3 is the amount (in moles) of the excess reactant that remains after the reaction has occurred as completely as possible.
5. Step 5: Always remember to check your answer to make sure it makes sense. The amount of the excess reactant that remains should be less than the initial amount of that reactant.

Key Concepts

Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions based on the balanced chemical equation. It allows us to determine the proportions of substances consumed and produced. In this case, understanding the stoichiometric ratios from the reaction equation is essential to identify how much of each reactant is needed and how much will remain after the reaction.

Limiting Reactant

The limiting reactant is the substance that is completely consumed first in a chemical reaction, thus determining the maximum amount of product that can be formed. Identifying the limiting reactant is crucial for calculating the amount of excess reactant left over after the reaction has occurred. In this scenario, we need to determine which reactant, FeS or HCl, limits the reaction to find the excess.

Mole Concept

The mole concept is a fundamental principle in chemistry that relates the amount of substance to its mass and the number of particles it contains. One mole of any substance contains Avogadro's number of entities (approximately 6.022 x 10²³). In this question, we use the mole concept to quantify the initial amounts of FeS and HCl, and to calculate how many moles remain after the reaction.