Question

15
if 3.75g of x reacts with 12.5g of y to form the compound xy, what is the percent by mass of x in the compound? (1 point)
76.9%
23.0%
30%
23.1%

Explanation:

Step1: Calculate the total mass of the compound

According to the law of conservation of mass, the mass of the compound \(XY\) is the sum of the masses of \(X\) and \(Y\).
\(m_{XY}=m_X + m_Y\)
Substitute \(m_X = 3.75g\) and \(m_Y=12.5g\) into the formula:
\(m_{XY}=3.75g + 12.5g=16.25g\)

Step2: Calculate the mass - percent of \(X\)

The formula for mass - percent is \(\text{Mass}\%=\frac{m_X}{m_{XY}}\times100\%\)
Substitute \(m_X = 3.75g\) and \(m_{XY}=16.25g\) into the formula:
\(\text{Mass}\%=\frac{3.75g}{16.25g}\times 100\%=\frac{375}{1625}\times100\% \)
\(\frac{375}{1625}=\frac{375\div25}{1625\div25}=\frac{15}{65}=\frac{3}{13}\approx0.2308\)
\(0.2308\times100\% = 23.1\%\)

Answer:

D. \(23.1\%\)