Question

The molecular weight of a compound is 329 g/mol and contains 1 mole of Na per mole of molecules. If the compound contain 12.8% nitrogen and 9.8% sulphur how many nitrogen and sulphur atoms are present per atom of sodium:
A. 2 and 1
B. 1 and 3
C. 1 and 2
D. 3 and 1

Answer 1

It is a numerically based question involving the mole concept. Here, first find out the mass of nitrogen, and sulphur present in the 329 g of the compound. Then, with the help of molar mass, and calculated mass, the atoms would be known.

Complete step by step answer:
-First, we are given the molecular weight of the compound, and the percentage of nitrogen, and sulphur present in the 329 g of the compound.
-Now, we know that the compound having a molecular weight 329 g/ mol contains 1 mole of Na.
-Here, we can say that 329 g of the compound contains $\dfrac{{12.8}}{{100}} \times 329$ of nitrogen, and $\dfrac{{9.8}}{{100}} \times 329$ of sulphur.
-By solving this we get,
-329 g of the compound contains 42 g of nitrogen and 32.2 g of sulphur.
-As we know that the molar mass or atomic mass of nitrogen, and sulphur are 14 g/mol, and 32 g/ mol respectively.
-Now, we will calculate the number of moles of nitrogen, and sulphur present in the compound having 329 g as the molecular weight.
-First, we will calculate the moles of nitrogen and that can be written as:
42/14 = 3 moles;
-Here, 42 g is the calculated mass, and 14 is the atomic mass
-Second, we have to calculate the moles of sulphur. It can be written as:
32.2/32 = 1 mole;
-Here, 32.2 is the calculated mass, and 32 is the atomic mass.
-In the last, we can say that the 3 nitrogen atoms are present per atom of sodium. 1 sulphur atom is present per atom of sodium.
Hence, the correct option is D.

Note: There is no need for confusion, just move step by step according to the values provided in the question. Sometimes, in the question, the percentage is not mentioned, and the direct values are being provided. The method to calculate the atoms will be the same. Calculate the number of moles from the data, and the answer would be known.