Determine Limiting Reagent

In this video we want to discuss how to determine the limiting reagent for mole concept questions, and use the limiting reagent to determine the amount of products formed.

Let's take a look at an example:

determine limiting reagent question

It is important for students not to assume that all the Na2CO3 will completely react with all the HCl.

We have to determine if one of the reactants is limiting, and therefore the amount of CO2 formed is based on the limiting reagent.

First let's calculate the amount of both reactants.

determine limiting reagent determine moles of reactants

Next, to determine the limiting reagent, we calculate the amount of reactant B required to completely react with all of reactant A.

In this case if we react 100% of Na2CO3 which is 0.05000 mol, how much of HCl is required?

determine limiting reagent determine which reactant is limiting

Based on the calculation, we need 0.1000 mol of HCl to react with 100% of Na2CO3, but we only have 0.08000 mol of HCl.

This means that HCl is limiting and Na2CO3 is in excess.

Sidenote:

If based on the calculation we have enough HCl to react with 100% of Na2CO3, this means after all the Na2CO3 is used up, we will still have excess HCl left.

In this case then Na2CO3 is limiting and HCl is in excess.

Finally we can use the limiting reagent to determine the amount and volume of CO2 produced.

determine limiting reagent determine amount of product based on limiting reagent

For the detailed step-by-step discussion on how to determine limiting reagent, check out this video!

Topic: Mole Concept, Physical Chemistry, A Level Chemistry, Singapore

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