Question

Two oxides of a metal contain 50% and 40% metal (M) respectively. If the formula of the first oxide is MO2, the formula of the second ixide is

(A)MO2
(B)MO3
(C)M2O
(D)M2O5

Answer 1

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Answer 2

Answer: (B) $MO_3$

Explanation: Let atomic weight of metal M be m:

moles of M=$\frac{\text {given mass}}{\text{ Molar mass}}=\frac{50}{m}$

moles of O=$\frac{\text {given mass}}{\text{ Molar mass}}=\frac{50}{16}$

Given the formula is $MO_2$

$\frac{\frac{50}{m}}{\frac{50}{16}}=\frac{1}{2}$

$m=32$

Now the second oxide contains 40% of metal:

Thus moles of M=$\frac{\text {given mass}}{\text{ Molar mass}}=\frac{40}{32}=1.25$

moles of O=$\frac{\text {given mass}}{\text{ Molar mass}}=\frac{60}{16}=3.75$

Thus formula of oxide is M:O= 1.25:3.75= 1:3.The formula is $MO_3$