Question

Calculate the percentage composition of chromium in potassium dichromate?

Answer 1

Step 1: Analyze the formula to find percentage composition

• The percentage composition of an element in a compound is given by

$\%\mathrm{composition}\mathrm{of}\mathrm{element}=\frac{\mathrm{Mass}\mathrm{of}\mathrm{element}\mathrm{in}\mathrm{compound}}{\mathrm{Mass}\mathrm{of}\mathrm{compound}}\times 100$

Step 2: Analyze the mass of chromium in compound

• The atomic mass of chromium ($\mathrm{Cr}$) is $52\mathrm{g}$
• In this compound i.e., potassium dichromate $\left({\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7\right)$, there are two chromium atoms present.
• So, the mass of element in the compound is $2\times 52=104\mathrm{g}$

Step 3: Find the molar mass of Potassium dichromate

• To find the molecular mass, we will add the atomic masses of all of the atoms in the molecule.
• So, the molecular mass of ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ $=(2\times 39)+(2\times 52)+(7\times 16)$

$$\begin{gathered} =78+104+112 \\ =294\mathrm{g}{\mathrm{mol}}^{-1} \end{gathered}$$

Step 4: Find the percentage composition of chromium

• $\%\mathrm{composition}\mathrm{of}\mathrm{Chromium}=\frac{\mathrm{Mass}\mathrm{of}\mathrm{Chromium}\mathrm{in}\mathrm{Potassium}\mathrm{Chromate}}{\mathrm{Mass}\mathrm{of}\mathrm{Potassium}\mathrm{Chromate}}\times 100$
• Putting the values:

$\%\mathrm{composition}\mathrm{of}\mathrm{Chromium}=\frac{104}{294}\times 100=35.37\%$

So, the percentage composition of chromium in potassium dichromate is $35.37\%$