Consider the reaction. 4 k(s) + o2(g) s 2 k2o(s) the molar mass of k is 39.09 g> mol and that of o 32.00 g> mol. without doing any calculations, pick the condi- tions under which potassium is the limiting reactant and explain your reasoning. a. 170 g k, 31 g o2 b. 16 g k, 2.5 g o2 c. 165 kg k, 28 kg o2 d. 1.5 g k, 0.38 g o2

Answer : The correct option is (d) 1.5 g K, 0.38 g O₂

Explanation :

The molar masses of potassium and oxygen are very close to each other. Therefore we can assume them to be equal. If we assume that, then according to reaction stoichiometry, 4 moles of K are needed to react with 1 mol of O₂. Since the molar masses are assumed to be equal , we can say that the mass of potassium needed to react with that of oxygen should be 4 times the mass of oxygen.

From the given options, the only option that has less amount of K is option d.

Here, 0.38 g of oxygen needs 0.38 x 4 = 1.52 g of K. But the given mass of potassium is 1.5 g which is less. This indicates that potassium is the limiting reactant as we do not have enough potassium to completely react with all of the oxygen.

Therefore option d is the correct option

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