Question

The percentage composition of $Cr$ in $K_2{Cr}_2{O}_7$ is (Given molar mass of $K_2{Cr}_2{O}_7=294.0g$ $mol$)

• A. $60.84$
• B. $28.54$
• C. $51.3$
• D. $35.37$

Answer 1

The correct option is D $35.37$

Given,

$K_{2}C{r}_2{O}_7$

Molar mass of $K_{2}C{r}_2{O}_7=294$ g/mol$⟶\left(1\right)$

Mass percentage=$\frac{Massofrequiredelementintotalsample}{Massoftotalsample}\times 100$

or mass percentage means, the amount of required element present in $100g$ of sample.

From, (1) $1$ mol i.e; $294g$ $K_{2}C{r}_2{O}_7$ contains $78g$ $K$, $104g$ $Cr$ & $112$ $O$

Now, if $294g$ $K_{2}C{r}_2{O}_7$ contains $104g$ $Cr$ then $100g$ sample of $K_{2}C{r}_2{O}_7$ would contain:

$\frac{100\times 104}{294}=35.374g$ of $Cr$

$\therefore$ Mass percentage of $Cr$ in $K_{2}C{r}_2{O}_7=35.37$%