In the reaction $MgCl _2+2 KOH \rightarrow Mg ( OH )_2+2 KCl$, if 3 moles $MgCl _2$ are added to 4 moles KOH, what determines how much $Mg ( OH )_2$ is made?
A. The amount of KOH
B. The amount of KCl
C. The amount of $MgCl _2+ KOH$
D. The amount of $MgCl _2$
Answer (1)
The balanced chemical equation is M g C l 2 + 2 K O H → M g ( O H ) 2 + 2 K Cl .
The stoichiometric ratio between M g C l 2 and K O H is 1:2.
3 moles of M g C l 2 require 6 moles of K O H for complete reaction, but only 4 moles of K O H are available.
Therefore, K O H is the limiting reactant, and the amount of M g ( O H ) 2 produced is determined by the amount of K O H . The answer is A .
Explanation
Understanding the Problem We are given the balanced chemical reaction: M g C l 2 + 2 K O H → M g ( O H ) 2 + 2 K Cl . We have 3 moles of M g C l 2 and 4 moles of K O H . We need to determine which reactant is the limiting reactant, as this will determine the amount of M g ( O H ) 2 produced.
Stoichiometric Ratio From the balanced equation, we see that 1 mole of M g C l 2 reacts with 2 moles of K O H . This gives us a stoichiometric ratio of 1:2 between M g C l 2 and K O H .
KOH Required for Complete Reaction of MgCl2 To react completely with 3 moles of M g C l 2 , we would need 3 m o l es M g C l 2 × 1 m o l e M g C l 2 2 m o l es K O H = 6 m o l es K O H . However, we only have 4 moles of K O H .
MgCl2 Required for Complete Reaction of KOH To react completely with 4 moles of K O H , we would need 4 m o l es K O H × 2 m o l es K O H 1 m o l e M g C l 2 = 2 m o l es M g C l 2 . We have 3 moles of M g C l 2 , which is more than enough to react with all the K O H .
Determining the Limiting Reactant Since we have less K O H than required to react with all the M g C l 2 , K O H is the limiting reactant. Therefore, the amount of M g ( O H ) 2 produced is determined by the amount of K O H available.
Final Answer The amount of M g ( O H ) 2 produced is determined by the limiting reactant, which is K O H . Therefore, the correct answer is A.
Examples
In a recipe, if you need 2 cups of flour for every 1 cup of sugar, and you have 4 cups of flour but only 1 cup of sugar, the amount of sugar will limit how much of the recipe you can make. Similarly, in chemical reactions, the limiting reactant determines the maximum amount of product that can be formed. This concept is crucial in industrial chemistry for optimizing production and minimizing waste.
