# Question #9c132

##### 1 Answer

We just may apply expression for molarity.

#### Explanation:

According to **molarity** (or **molar concentration**) expression:

We know that

Now, let us calculate the mass of

- For carbon, C, we know that there are 16 atoms for every molecule of methylene blue. Its atomic mass is 12.01 amu (atomic mass units), so there are
#12.01 cdot 16 = color(blue) 192.16# amu of C per molecule. Analogously, we can say that there are 192.16 g of C per mol of methylene blue (atomic mass on amu and molar mass on g/mol are equivalent).

We just may apply this method to all the elements on methylene blue molecule:

- For hydrogen:
#1.01 cdot 18 = color(blue) 18.18# g/mol. - For nitrogen:
#14.01 cdot 3 = color(blue) 42.03# g/mol. - For sulphur:
#32.07 cdot 1 = color(blue) 32.07# g/mol. - For chlorine:
#35.43 cdot 1 = color(blue) 35.43# g/mol.

The sum of all being:

If we need 0.04 mol of