What three conversion factors and in what order would you use them to convert the mass of a compound into atoms of a articular element in that compound-- for e

Question

What three conversion factors and in what order would you use them to convert the mass of a compound into atoms of a articular element in that compound-- for example, from 1.00 g aspirin (C9H8O4) to number of hydrogen atoms in the 1.00-g sample?

Answer 1

The simplest way to approach this problem is by using dimensional analysis.  The three conversions in order would be

1. convert grams of aspirin to moles of aspirin
2. convert moles of aspirin to molecules of aspirin
3. convert molecules of aspirin to atoms of hydrogen

 

1. 1.00 g x 1 mol/180 g = 0.00556 moles aspirin
2. 0.00556 moles x 6.02x10²³ molecules/mole = 3.35x10^21 molecules
3. 3.35x10²¹ molecules x 8 H atoms/molecule = 2.68x10²² hydrogen atoms (to three significant figures)

 

Answer 2

How about this?

 

Adding up the atomic weights:

 

  9*12 + 8*1 + 4 * 16 = 108 + 8 + 64 = 180 grams per mole

 

 The hydrogen is 8/180 =   4.44....%

 

4.44% * 1 gram of aspirin x 1 mole of aspirin/180 grams per mole x 6.02 x 10^23

 

where 6.02 x 10^23 is Avogradro's number

 

you get something along the order of 20, like

 

1.4 x 10^20