Question

You have 1.20 x 10 24 molecules of H2O. What is the mass of this sample?

Answer 1

`35.86~g~H_2O`

Step-by-step explanation:

In this case, we have to remember that relationship between the avogadro's number and the "mol" concept:

`1~mol=6.023x10^2^3~molcules`

With this in mind, we can do the first conversion:

`1.20x10^2^4~molecules~of~H_2O(1~mol_H_2O)/(6.023x10^2^3~molcules~of~H_2O)=1.99~mol_H_2O`

Now, if we calculate the molar mass of
`H_2O`. The atomic mass of O is 16 g/mol and the atomic mass of H is 1 g/mol, so:

(16*1)+(1*2)= 18 g/mol

In other words,
`1~mol~H_2O=~18~g~H_2O`, so:

`1.99~mol_H_2O(18~g~H_2O)/(1~mol~H_2O)=35.86~g~H_2O`

I hope it helps!