Question

question 1
1 point
a 15.5 gram sample of diphosphorous pentoxide contains how many grams of phosphorous?
a 1.69
b 6.76
c 3.38
d 13.5

Explanation:

Step1: Calculate molar mass of \(P_2O_5\)

Molar mass of \(P = 30.97\ g/mol\), molar mass of \(O=16.00\ g/mol\).
Molar mass of \(P_2O_5=(2\times30.97)+(5\times16.00)=61.94 + 80.00=141.94\ g/mol\)

Step2: Calculate mass of \(P\) in \(P_2O_5\)

In \(P_2O_5\), there are 2 moles of \(P\). Mass of \(P\) in \(1\) mole of \(P_2O_5\) is \(2\times30.97 = 61.94\ g\)
Mass fraction of \(P\) in \(P_2O_5=\frac{61.94}{141.94}\)
Mass of \(P\) in \(15.5\ g\) of \(P_2O_5=15.5\times\frac{61.94}{141.94}\)
\(15.5\times\frac{61.94}{141.94}=\frac{15.5\times61.94}{141.94}=\frac{960.07}{141.94}\approx6.76\ g\)

Answer:

B. 6.76