Question

What is the mass of one molecule of yellow phosphorus ? (Atomic mass, $P = 30$)

• A. $1.993 \times 10^{-22} \, kg$
• B. $1.993 \times 10^{-19} \, mg$
• C. $4.983 \times 10^{-20} \, mg$
• D. $4.983 \times 10^{-23} \, kg$

Answer 1

Answer: (B)

Yellow phosphorus is an impure form of white phosphorus $\left(P_{4}\right)$

Molecular mass of yellow phosphorus $\left( P _{4}\right)$

$=4 \times 30=120$

$\therefore $ According to Avogadro's hypothesis,

Mass of $6.022 \times 10^{23}$ molecules $=120 g$

and mass of 1 molecule

$=\frac{120 \times 1}{6.022 \times 10^{23}}$

$=19.926 \times 10^{-23} g$

$=1.993 \times 10^{-22} g$

$=1.993 \times 10^{-19} mg$