Question

how many molecules of watwr and oxygen atoms are present in 0.9 g of water ?

Answer 1

Molecular mass of H2O = 18g/mol
Number of molecules present in 18g of H2O = 6.022×1023 molecules

Number of molecules present in 0.9g of H2O = 6.022×102318×0.9 molecules

Number of atoms in 1 molecule = 3 (2 hydrogen and 1 oxygen)

Number of atoms in ​ 6.022×102318×0.9 molecules or 0.9g of H2O = ​ 6.022×102318×0.9×3 = 9.03×1022 atoms

Answer 2

Molecular mass of H2O = 18g/mol

Numbers of molecules present in 18g of H2O =6.022×10^23 molecules

Numbers of molecules present in 0.9g of

H2O = 6.022×10^23×18×0.9 molecules

Numbers of atom in 1 molecule 3(2hydrogen and 1 oxygen)

Number of atoms in

6.022×10^23×18×0.9 molecules of

H2O =

6.022×10^23×0.9×3

= 9.03×10^22 atoms.

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