Question

If a copper – containing compound contains \[4.999%\]\[Cu\]by mass and there are \[2\]copper atoms per formula unit, what is the molar mass of the compound?

A) \[2547g/mol\]
B) \[47.50g/mol\]
C) \[31.75g/mol\]
D) \[1274g/mol\]

Answer 1

Hint : In order to solve this question first determine the number of atoms per formula unit. Then we would multiply the atomic weight of elements with its atomic number.

Complete step-by-step solution:
 let us assume the molar mass of compound \[=\]\[M\]
According to the question there are two Copper atoms in \[1mole\]of atom i.e. \[128gms\] of atom,
Here, copper mass is given \[4.999%\]
Now, we will calculate the molar mass of the compound-
\[\begin{align}
  & \Rightarrow \left( \dfrac{4.999}{100} \right)\times M=128gms \\
 & \Rightarrow M=\dfrac{12800}{4.99}=2547g/mol \\
\end{align}\]
So, the right option is a) \[2547g/mol\].

Note: Italian physicist Amedeo Avogadro found the concept of molar mass. Molar mass is mainly used to convert a mass to an amount of substance that is expressed as atoms, molecules, and the ions.
\[%\]of copper) \[\times \]Molar mass \[=\]Mass of copper