Question

How many molecules are in 10.8 grams of `C_12H_22O_11`?

Answer 1

`1.901 xx 10^22`

Explanation:

The question is how many molecules are in a determined amount of an specific compound.

First step to obtain the number of moles, that is the mass/MW

`"no. of moles" = "mass"/"molar mass"`

The MW in this case is the sum of the atomic weights of the different atoms in the composition of the compound.

For this specific case it is `C_12H_22O_11`, is possible for a fast calculation to use the integer weights for `C`, `H` and `O`, `12`, `1` and `16` respectively.

Then MW `= 12(12) + 22(1) + 11(16) = "342 g/mol"`

moles `= "mass"/"MW" = ("10.8 g"/"342 g/mol") = "0.03157 moles"`

The number of molecules per mol is defined by the Avogadro's number `6.0221409 xx 10^23`,

Giving up the numer of molecules as

`0.03157 xx 6.022 xx 10^23 = 1.901 xx 10^22`