Question

Consider the figure below, in which the blue circles represent atoms of copper metal, atomic mass $63.5amu$, while the red circles represent atoms in zinc metal, atomic mass $65.4amu$.
Here are four statements concerning this system. Identify the correct statement or statements.
I. This is a single-phase mixture, with a copper-to-zinc atom ratio of $3:1$.
II. This is two-phase mixture, with a copper-to-zinc atom ratio of $8:1$.
III. The mixture is $80$% copper, by mass.
IV. This mixture could be an alloy of copper and zinc.

• A. Statement I only.
• B. Statement II only.
• C. Statement I and III only.
• D. Statement I and IV only.

Answer 1

Answer: (C)

Statement I and III only.

Here, no. of atoms of $Cu=30atoms$

No. of atoms of $Zn=10atoms$

Single phase mixture is a homogenous mixture with same proportions of atoms.

Here, the ratio of copper to zinc is $3:1$

So, it is a two phase mixture.

$\Rightarrow \%Cu$ by mass $=\frac{3\times 63.5}{3\times 63.5+65.4}=\frac{190.5}{255.9}=0.744\times 100=74\%\approx 80\%$ by mass

The mixture can be alloy of zinc.