Question

calculate the number of atom and molecules in 10g of O2

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Answer 1

Answer:

10.0g O2 x (1 mol O2 / 32.0g O2) x (6.022x10^23 molecules O2 / 1 mol O2) = 1.88x10^23 molecules O2

We assumed a mass of 10.0g which is expressed to three significant digits, rather than the one significant digit in 10g, which would limit your answer to one significant digit.

Since 1 mol is equivalent to the molar mass, and 1 mol is equivalent to Avogadro’s number, the 1 molar mass is equivalent to Avogadro’s number, and we can use just one conversion factor:

10.0g O2 x (6.022x10^23 molecules O2 / 32.0g O2) = 1.88x10^23 molecules O2

The point in this answer is to illustrate the use of the unit-factor method and to review significant digits.