Question

a 48 g sample is composed of 38 g of fluorine (f) and 10 g of boron (b). what is the percent by mass of f in the sample?
79%
21%
75%
64%

Explanation:

Step1: Recall mass percent formula

Percent by mass of F = $\frac{\text{Mass of F}}{\text{Total mass of sample}} \times 100\%$

Step2: Plug in given values

Substitute mass of F = 38 g, total mass = 48 g
$\text{Percent by mass of F} = \frac{38}{48} \times 100\%$

Step3: Calculate the value

$\frac{38}{48} \approx 0.7917$, so $0.7917 \times 100\% \approx 79\%$

Answer:

79%