Question

Which reactant is the limiting reagent and which is in excess?
A.${{K}_{2}}[PtC{{l}_{4}}]$ and $N{{H}_{3}}$ respectively
B. $N{{H}_{3}}$ and ${{K}_{2}}[PtC{{l}_{4}}]$ respectively
C. Both A and B
D. None of the above

Answer 1

Hint: To solve this question, you first have to consider what a limiting reagent is. A limiting reagent is a reactant which is consumed completely to form a product during a reaction. The one that is in excess is the reactant that remains even after the reaction is completed and the other reactant is exhausted.

Complete answer:
Consider the reaction for these reagents,
\[{{K}_{2}}[PtC{{l}_{4}}]+2N{{H}_{3}}\xrightarrow{\Delta }Pt{{(N{{H}_{3}})}_{2}}C{{l}_{2}}+2KCl\]
The limiting reagent can only be determined when the values for the amount of reactants is taken. Any reactant can become the limiting reagent depending on the quantity in which it is available. Equations and theoretical reactions cannot have limiting reagents, only real world reactions have them. Any minor human error can contribute to one of the reactants becoming the limiting reagent.
Therefore, the answer is C. Both A and B

Additional Information:
You can find out the limiting reagent if the weights are given using a simple trick.
-Calculate the number of moles available of the given reactants.
-Balance the chemical reaction.
-Divide the number of moles calculated by the stoichiometric coefficients in the balanced reaction.
-The reactant that has the lowest ratio is the limiting reagent.
Another thing of note is that the compound $Pt{{(N{{H}_{3}})}_{2}}C{{l}_{2}}$ that is formed during this reaction is called ‘cisplatin’. It is a very well known anti-cancer drug and has extensive use in chemotherapy to either inhibit the growth of the tumour cells or to abolish them entirely.

Note: Do not mark answer ‘D. None of the above’ as the correct answer. If one of the reactants is the limiting reagent then the other is definitely going to be present in excess. A reaction in the real world is always going to have a limiting reagent and an excess reagent.