The simplest formula of a substance is found to be CH₂O, and its approximate molecular weight is found by experiment to be 93. What is the exact molecular weight of this substance in grams/mole?

Question

Quizplus · Accepted Answer

The molecular weight can be calculated by adding up the atomic weights of each element in the formula. Using the periodic table, we find that:

- C (carbon) has an atomic weight of 12.011
- H (hydrogen) has an atomic weight of 1.008
- S (sulfur) has an atomic weight of 32.06
- U (uranium) has an atomic weight of 238.03
- B (boron) has an atomic weight of 10.81
- O (oxygen) has an atomic weight of 15.999

So the molecular weight is:

(1 x 12.011) + (1 x 1.008) + (1 x 32.06) + (1 x 238.03) + (12 x 10.81) + (1 x 15.999) = 696.1 g/mol.

However, the question asks for the exact molecular weight in grams/mole, and the answer choices are all given to one decimal place. The closest choice is C) 90.1 g/mol, which is the same as rounding 696.1 to one decimal place.

The Simplest Formula of a Substance Is Found to Be