Question

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

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Answer 1

For calculating the mass, we need to first calculate the number of moles from 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 = $\frac{Totalnumberofmolecules}{Avogadroconstant}\times MolecularMass$

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

⇒ Mass = 1440.71 g