Question

Find the expected percent composition of copper and chloride in the compounds copper(I) chloride (CuCl) and copper(II) chloride (CuCl2). To find the percentages, divide the molar mass of the element by the molar mass of the compound.

Answer 1

As the questions says, we can calculate the percent composition of each element in a compound by dividing the molar mass of the corresponding element in the compound by the molar mass of the compound.

The molar masses of Cu and Cl are:

`\begin{gathered} M_(Cu)=63.546 \\ M_(Cl)=35.453 \end{gathered}`

Thus, the molar masses of CuCl and CuCl₂ are:

`\begin{gathered} M_(CuCl)=1\cdot M_(Cu)+1\cdot M_(Cl)=(1\cdot63.546+1\cdot35.453)g\cdot mol^(-1)=98.999g\cdot mol^(-1) \\ M_(CuCl_2)=1\cdot M_(Cu)+2\cdot M_(Cl)=(1\cdot63.546+2\cdot35.453)g\cdot mol^(-1)=134.452g\cdot mol^(-1) \end{gathered}`

So, the percent compositions of copper and chlorine in CuCl are:

`\begin{gathered} P_(Cu|CuCl)=(M_(Cu))/(M_(CuCl)) \\ P_(Cu|CuCl)=\frac{63.546g\cdot mol^(-1)_{}}{98.999g\cdot mol^(-1)} \\ P_(Cu|CuCl)\approx0.6419=64.19\% \end{gathered}`
`\begin{gathered} P_(Cl|CuCl)=(M_(Cl))/(M_(CuCl)) \\ P_(Cl|CuCl)=\frac{35.453g\cdot mol^(-1)_{}}{98.999g\cdot mol^(-1)} \\ P_(Cl|CuCl)\approx0.3581=35.81\% \end{gathered}`

For CuCl₂, we need to consider two Cl, so:

`M_(Cl_2)=2\cdot M_(Cl)=2\cdot35.453g\cdot mol^(-1)=70.906g\cdot mol^(-1)`

The percent compositions of copper and chlorine in CuCl₂ are:

`\begin{gathered} P_(Cu|CuCl_2)=\frac{M_(Cu)}{M_{CuCl_(2)}} \\ P_(Cu|CuCl_2)=\frac{63.546g\cdot mol^(-1)_{}}{134.452g\cdot mol^(-1)} \\ P_(Cu|CuCl_2)\approx0.4726=47.26\% \end{gathered}`

`\begin{gathered} P_Cl=\frac{M_{Cl_(2)}}{M_{CuCl_(2)}} \\ P_Cl=\frac{70.906g\cdot mol^(-1)_{}}{134.452g\cdot mol^(-1)} \\ P_CuCl_(2)\approx0.5274=52.74\% \end{gathered}`

Answers:

For CuCl:

Percent composition of copper is approximately 64.19%.

Percent composition of chlorine is approximately 35.81%.

For CuCl₂:

Percent composition of copper is approximately 47.26%.

Percent composition of chlorine is approximately 52.74%.