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Solutions: Limiting Reagents (Worksheet)

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Work in groups on these problems. You should try to answer the questions without referring to your textbook. If you get stuck, try asking another group for help.

Q1.

Given the following reaction:                                        (hint: balance the equation first)

    \(Ca(OH)_2 + H_2SO_4 \rightarrow CaSO_4 + 2H_2O\)

If you start with 14.82 g of  \(Ca(OH)_2\) and 16.35 g of \(H_2SO_4\),

a)  determine the limiting reagent

b)  determine the number of moles of \(H_2O\) produced

c)  determine the number of grams of \(CaSO_4\) produced

d)  determine the number of grams of excess reagent left

1) make sure the equation is balanced.

This equation is already balanced.

2) then determine the moles of each compound that you have.

3) based on the moles that you have, calculate the moles that you need of the other reagent to react with each of those amounts.


4)  compare what you have to what you need.  If you have more than you need, this is the reagent in excess (xs).  If you have less than you need, this is the limiting reagent (LR).

You have 0.20 mol of \(Ca(OH)_2\) and you need 0.17 mol \(Ca(OH)_2\).  This reagent is in xs.
You have 0.17 mol of \(H_2SO_4\) and you need 0.20 mol \(H_2SO_4\).  This reagent is the LR

To determine the amounts of product (either grams or moles), you must start with the limiting reagent.  Use the amount that you have, not the amount you need.

To determine the grams of excess reagent, subtract the amount you need from the amount that you have, then using the molar mass, convert the moles left to grams.