Question

A compound possesses 8% sulfur by mass. The least molecular mass is:
A. 200
B. 400
C. 155
D. 355

Answer 1

Hint: As the question is asking for the least molecular mass, you have to consider just one atom of sulfur in the compound. Now, use the given values and calculate the value for the least molecular mass of the atom.

Complete step by step answer:

We are given a compound that possesses 8% sulfur by mass. So, if we assume we have 100 g of the compound then it will be having 8 g of sulfur.
Now, we know that the molecular weight of sulfur is 32 g.
A compound must contain at least one atom of sulfur because partial atom is not possible. So, we can say one atom of sulfur will be present in the compound.
Hence,
8 g of sulfur is present in 100 g of the compound
1 g of sulfur would be present in $\dfrac { 100 }{ 8 }$ g of the compound
Then, 32 g of sulfur will be present in, $\dfrac { 100 }{ 8 }$ x 32 = 400 g of the compound.

Therefore, we can conclude that the correct answer to this question is option B.

Additional information:
Sulfur is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent, and nonmetallic.
Elemental sulfur is a bright yellow, crystalline solid at room temperature.

Note: We should know the difference between molecular mass and molar mass -
The molecular mass of one molecule is its mass expressed in unified atomic mass units (1/12 the mass of one atom of the isotope carbon-12).
The molar mass is defined as the mass of a sample of that compound divided by the amount of substance in that sample, measured in moles.