Question

Calculate the percentage composition of chromium in potassium dichromate?

Answer 1

`35.35%`

Explanation:

Percentage composition of an element in a compound is given by

`"% composition of element" = "Mass of element in compound"/"Mass of compound" × 100`

Let’s say we have `1` mol of potassium dichromate (`"K"_2"Cr"_2"O"_7`)

Mass of `"1 mol"` of compound `"= 294.185 g"`

Mass of `"Cr"` in `"1 mol"` of compound `"= 2 × 52 g = 104 g"`

`"% composition of Cr" = "104 g"/"294.185 g" × 100 = color(blue)(35.35%)`

Answer 2

The percent composition of chromium in potassium chromate is `"35.3495%"`.

Explanation:

The chemical formula for potassium dichromate is `"K"_2"Cr"_2"O"_7"`. Its molar mass is `"294.182 g/mol"`. (https://pubchem.ncbi.nlm.nih.gov/compound/potassium_dichromate)

One mole of potassium dichromate contains two moles of chromium. Determine the mass of chromium by multiplying its subscript `2` by its molar mass (atomic weight on the periodic table in g/mol), `"51.996 g/mol"`.

`M_"Cr"=(2xx"51.996 g/mol")="103.992 g/mol"`

To determine the percentage composition of an element in a compound, use the following equation.

`"% composition of element"=("mass of element in compound")/("molar mass of compound")xx100%`

Plug in the known vales and solve for percent composition of `"Cr"`.

`"% composition Cr"=(103.992color(red)cancel(color(black)("g"/"mol")))/(294.182color(red)cancel(color(black)("g"/"mol")))xx100%="35.3495%"`

The percent composition of chromium in potassium chromate is `"35.3495%"`.