Some Basic Concepts of Chemistry Part 3

Concept:In a chemical reaction, the limiting reagent is the reactant that gets completely consumed first and limits the amount of product formed.Explanation:The balanced reaction is $A + 2B \rightarrow AB_2$.First, calculate the moles of each reactant.Moles of $A$: $n_A = \frac{36.0}{60} = 0.60$ mol.Moles of $B$: $n_B = \frac{56.0}{80} = 0.70$ mol.To find the limiting reagent, compare the required moles of $B$ for the given moles of $A$.For $0.60$ mol of $A$, the required moles of $B$ are $2 \times 0.60 = 1.20$ mol.But only $0.70$ mol of $B$ is available, which is less than required.Thus, $B$ is the limiting reagent.So statement A is false.Now, calculate the amount of product formed.From the reaction, $2$ mol of $B$ produce $1$ mol of $AB_2$.Moles of $AB_2$ formed: $n_{AB_2} = \frac{0.70}{2} = 0.35$ mol.Molar mass of $AB_2$: $M_{AB_2} = 60 + 2(80) = 220$ g mol$^{-1}$.So statement C is false.Mass of $AB_2$ formed: $0.35 \times 220 = 77.0$ g.So statement B is true.Now, find the amount of $A$ left unreacted.The mole ratio of $A$ consumed to $AB_2$ formed is $1:1$, so moles of $A$ consumed = $0.35$ mol.Mass of $A$ consumed: $0.35 \times 60 = 21.0$ g.Unreacted $A$ = initial mass - consumed mass = $36.0 - 21.0 = 15.0$ g.So statement D is true.Thus, only statements B and D are correct.The correct option is D.Answer:D. B and D Only