Number of atoms: How many `C` atoms are present in `342.3g` of table sugar or surose `(C_(12) H_(22) O_(11)` ?
Strategy : The molecule mass of surcrose is `342.3 u`. Thus, its molar mass is 342.3 g. First calculate the number of moles, then calculate the number of molecules, and finally use the information that there are `12 C` atoms in every molecule to find the number of `C` atoms.
grams `rarr` moles of sucrose `rarr` molecules of surcrose
`rarr` number of `C` atoms

Explanation

Step 1: Number of sucrose moles `= ("Mass of sucrose")/("Molar mass of sucrose")`
`= (34.23 g)/(342.3 "g mol"^(-1))`
`= 0.1 mol` sucrose
step 2: Number of sucrose molecules
(Number of sucrose moles)`xx` (Avogadro's constant)
`= (0.1 mol) (6.022xx10^(23)` molecules `mol^(-1)`)
`= (6.022xx10^(22)` sucrose molecules
step 3: Number of `C` atoms
`= ("Number of sucrose molecules") xx ("number of C atoms per sucrose molecule")`
`(6.022xx10^(22)xx10^(22)` molecules) (12 C atoms `"molecule"^(-1)`)
`= 7.266xx10^(3) C` atoms
One step calculation using conversion factors :
`34.23g "sucrose" xx ("1 mol sucrose")/("342.3g sucrose")`
`xx (6.022xx10^(23) "Source molecules")/("1 mol sucrose") xx ("12C atoms")/("1 sucrose molecule")`
`= 7.26xx10^(23) C` atoms