Question

An oxide of metal contains 40% oxygen by weight. What is the equivalent weight of metals?

Answer 1

Hint: The total mass percentage of metal oxide is 100 %. In metal oxide the milliequivalent of metal is the same as the milliequivalent of oxide. The millie equivalent of an atom is calculated by dividing the mass by the equivalent weight. The equivalent weight of the atom is calculated by dividing the molecular weight by the valency factor.

Complete step by step answer:
Given,
40 % oxygen by weight
Assume that the total mass of metal oxide is 100g.
Where, the mass of oxygen is 40g.
The remaining mass 100 g – 40g = 60g is of metal.
As, we know that the milliequivalent of metal is equal to milliequivalent of oxygen.
$m.eq\;of\;Metal = m.eq\;of\;oxygen$…….(i)
The millie equivalent of atom is calculated by dividing mass of atom divided by the equivalent weight.
The formula to calculate the milliequivalent is shown below.
$m.eq = \dfrac{{mass}}{{Eq.wt}}$……..(ii)
The equivalent weight is defined as the mass of the substance present in grams which is chemically equivalent to the eight grams of oxygen atom and one gram of hydrogen atom.
The formula to calculate the equivalent weight is shown below.
\[E = \dfrac{M}{V}\]………(iii)
Where,
E is the equivalent weight
M is the molecular weight
V is the valency factor
The valency of oxygen is 2.
The molecular weight of the oxygen is 16.
To calculate the equivalent weight of the metal, substitute, the values in equation (i)
\[\Rightarrow \dfrac{{60}}{E} = \dfrac{{40}}{{\dfrac{{16}}{2}}}\]
\[\Rightarrow \dfrac{{60}}{E} = \dfrac{{40}}{8}\]
\[\Rightarrow E = \dfrac{{60 \times 8}}{{40}}\]
\[\Rightarrow E = 12\]
Therefore, the equivalent weight of the metal is 12.

Note: Make sure to determine the valency of oxygen and the molecular weight as the only molecule known is oxygen and metal is unknown therefore we cannot determine its molecular weight.