Question

What is the mass of 4.82 x ${10}^{25}$ molecules of $H_{2}O$ in grams?

• A. 1440.71g
• B. 1540.71 g
• C. 1770.51 g
• D. 1420.91 g

Answer 1

The correct option is

B

1440.71 g

For calculating the mass, we need to first calculate the number of moles of the given number of molecules.

Mass = Number of moles x Molecular Mass

Since, number of moles is given by:

Number of moles = $\frac{Totalnumberofmolecules}{Avogadroconstant}$

Therefore, Mass = $\frac{Totalnumberofmolecules}{Avogadroconstant}\times MolecularMass$

As we know that,The molecular mass of water = 18 g/mole

⇒ Mass = $\frac{4.82\times {10}^{25}}{6.022\times {10}^{23}}\times 18$

⇒ Mass = 1440.71 g