Consider the following reaction. K₂CO₃ plus 2HCl react to form 2KCl plus CO₂ plus H₂O. If 6.0 moles of HCl is available to the reaction with an unlimited supply of K₂CO₃, how many moles of CO₂ can be produced? A) 1.0 moles, B) 1.5 moles, C) 2.0 moles, D) 3.0 moles, or E) 6.0 moles.
What we’re looking at here is the reaction of potassium carbonate, K₂CO₃, with hydrochloric acid, HCl. The products are potassium chloride, carbon dioxide, and water. This is an example of the classic metal carbonate plus acid reaction. The question tells us we’re starting off with 6.0 moles of hydrogen chloride, HCl.
Just in case you’re wondering, I’m just gonna clear up something simple. When HCl is a gas on its own, we call it hydrogen chloride. When it’s dissolved in water, it’s called hydrochloric acid. There aren’t any state symbols in the equation, so we can’t be sure whether it’s hydrogen chloride or hydrochloric acid. But for the sake of this question, it doesn’t make a difference. So, I’m going to assume that we’re dealing with the reaction of solid potassium carbonate and hydrochloric acid solution.
The question tells us that we have an unlimited supply of potassium carbonate. So, our limiting reagent in this case is hydrochloric acid. Our job is to figure out how many moles of carbon dioxide can be produced when we react this much HCl with potassium carbonate. For that, we need the molar ratio between HCl in and carbon dioxide out. That ratio is two to one. For every two units of HCl we consume, we produce one molecule of carbon dioxide.
We can calculate the amount of CO₂ we might produce by taking the amount of HCl, 6.0 moles, and multiplying it by one mole of carbon dioxide per two moles of HCl, giving us 3.0 moles of carbon dioxide. The question asks us to find the amount of carbon dioxide that can be produced. From this, we take it to mean that we’re looking for the maximum amount of carbon dioxide we could produce if we put 6.0 moles of HCl in. And our answer is 3.0 moles of carbon dioxide.