calculate number of molecules of oxygen in 6.4g of oxygen?

Mass of oxygen = 6.4g

Molecular mass of oxygen = 32g

Number of moles = mass / molecular mass = 6.4 / 32 = 0.2 moles

Number of molecules = Avogadro number X number of moles

 = 6.023 X 1023 X 0.2 = 4.80 X 1023 molecules

So 6.4g of oxygen contains 4.80 X 1023 molecules.

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16g--------1mole

6.4g-------?

?=6.4g/16g

    =0.4mole

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we know that:                                                                                                                                                                                                        16g of oxygen contains = 6.022 x 10^23 molecules                                                                                         thereforce,   6.4g of oxygen contains = 6.022 x 10^23 x 6.4/ 16 = 24.088 x 10^23 molecules                      

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