Recall that mass percent is given by:

$\overline{){\mathbf{\%}}{\mathbf{}}{\mathbf{mass}}{\mathbf{=}}\frac{\mathbf{mass}\mathbf{}\mathbf{of}\mathbf{}\mathbf{X}}{\mathbf{total}\mathbf{}\mathbf{mass}}{\mathbf{\times}}{\mathbf{100}}}$

Recall that the mass percentages of a compound must add up to 100%.

This means:

**%V + %O = 100%**

**%O = 100% – 68% = 32% O**

Assuming we have 100 g of the compound, this means we have 68 g V and 32 g O.

Now, we need to get the moles of each element in the compound.

The atomic masses are 50.94 g/mol V and 16.00 g/mol O.

$\mathbf{68}\mathbf{}\overline{)\mathbf{g}\mathbf{}\mathbf{V}}\mathbf{\times}\frac{\mathbf{1}\mathbf{}\mathbf{mol}\mathbf{}\mathbf{V}}{\mathbf{50}\mathbf{.}\mathbf{94}\mathbf{}\overline{)\mathbf{g}\mathbf{}\mathbf{V}}}$ **= 1.33 mol V**

$\mathbf{32}\mathbf{}\overline{)\mathbf{g}\mathbf{}\mathbf{O}}\mathbf{\times}\frac{\mathbf{1}\mathbf{}\mathbf{mol}\mathbf{}\mathbf{O}}{\mathbf{16}\mathbf{.}\mathbf{00}\mathbf{}\overline{)\mathbf{g}\mathbf{}\mathbf{O}}}$** = 2.00 mol O**

Divide the number of moles of each by the smallest value.

Vanadium forms four different oxides in which the percent by mass of vanadium is respectively 76%, 68%, 61%, and 56%.

Give the name of the second oxide.

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