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Question

A certain metal oxide has the formula MO where M denotes the metal. A 39.46g sample of the compound is strongly heated in an atmosphere of hydrogen to remove oxygen as water molecules. At the end, 31.70g of the metal is left over. If O has an atomic mass of 16.00 amu, calculate the atomic mass of M and identigy the element.

For this question the answers where Atomic Mass: 65.4 amu and element: Zn

but I don't know how to solve this.

My textbook doesn't have any examples like this question.

Answer 1

Use proportions.
The mass of the oxide before and after reduction contain the same amount of metal. The masses are proportional to the sum of the AMU's:
(M+16)/M = 39.46/31.7
Cross multiply to get
31.7(M+16) = 39.46M
Solve for M to get
M=64.87
which lies between Cu at 63.55 and Zn at 65.39.
Margin of error required if the metal is Zn: (65.39-64.87)/65.39= 0.8%
which could be acceptable depending on the laboratory conditions.

Answer 2

Thank you