Answer
The mass of $CaWO_4$=622.94g
Work Step by Step
Tungsten molar mass=183.84amu
$FeWO_4$ molar mass=303.68amu
$CaWO_4$ molar mass=287.93amu
First, we calculate the percent composition of tungsten in $FeWO_4$ using the formula:
Percent composition of tungsten=$\frac{\text{molar mass tungsten}}{\text{total molar mass}}\times100=\frac{183.84}{303.68}\times100\approx60.54\%$
Then we calculate the mass of Tungsten in 657g $FeWO_4$ using the formula:
Mass of Tungstin=Total mass of $FeWO_4$$\times$ Percent composition of Tungsten=$657\times60.54\%\approx397.75g$
The percent composition of tungsten in $CaWO_4$:
Percent composition of tungsten=$\frac{\text{molar mass tungsten}}{\text{total molar mass}}\times100=\frac{183.84}{287.93}\times100\approx63.85\%$
Let the mass of $CaWO_4$ be $x$
Mass of Tungstin=Total mass of $CaWO_4$$\times$ Percent composition of Tungsten
$397.75=x\times63.85\%$
$x=\frac{397.75}{63.85\%}\approx622.94g$
The mass of $CaWO_4$=622.94g
