Answer
a. Mass of a Br atom = 1.33 x $10^{-22}$ g
b. Mass of a Te atom = 2.12 x $10^{-22}$ g
c. Mass of a P$Br_{3}$ molecule = 4.496 x $10^{-22}$ g
d. Mass of a Fe$(OH)_{2}$ formula unit = 1.493 x $10^{-22}$ g
Work Step by Step
Strategy: To calculate the mass of one atom, molecule, or formula unit, we should use:1- Molar mass, that is the mass of one mole of substance 2- relationship of mole and Avogadro's number .
a. Mass of Br atom. The molar mass of Br is 79.904 g/mol. 1 mol Br has Avogadro's number atoms that is 6.02 x $10^{23}$.
Mass of a Br atom = $\frac{molar mass Br}{Avogadro's number}$
Mass of a Br atom = $\frac{79.904g}{6.02 \times 10^{23}}$
Mass of a Br atom = 13.27 x $10^{-23}$ g
Mass of a Br atom = 1.327 x $10^{-22}$ g
b. Mass of Te atom. The molar mass of Te is 127.60 g/mol. 1 mol Br has Avogadro's number atoms that is 6.02 x $10^{23}$.
Mass of a Te atom = $\frac{molar mass Te}{Avogadro's number}$
Mass of a Te atom = $\frac{127.60g}{6.02 \times 10^{23}}$
Mass of a Te atom = 21.20 x $10^{-23}$ g
Mass of a Te atom = 2.12 x $10^{-22}$ g
c. Mass of P$Br_{3}$ molecule.
Molar mass of P$Br_{3}$ =30.973 + 3 x 79.904
Molar mass of P$Br_{3}$ = 270.685 g/mol
1 mol P$Br_{3}$ has Avogadro's number atoms that is 6.02 x $10^{23}$.
Mass of a P$Br_{3}$ molecule = $\frac{molar mass_{P$Br_{3}$ }}{Avogadro's number}$
Mass of a P$Br_{3}$ molecule = $\frac{270.685 g}{6.02 \times10^{23}}$
Mass of a P$Br_{3}$ molecule = 44.96 x $10^{-23}$ g
Mass of a P$Br_{3}$ molecule = 4.496 x $10^{-22}$ g
d. Mass of Fe$(OH)_{2}$ formula unit.
Molar mass Fe$(OH)_{2}$ = 1 X 55.845 + 2 x 15.999 + 2 x 1.007
Molar mass Fe$(OH)_{2}$ = 89.857 g
Mass of a Fe$(OH)_{2}$ formula unit = $\frac{molar mass_Fe(OH)_{2}}{Avogadro's number}$
Mass of a Fe$(OH)_{2}$ formula unit = $\frac{89.857 g}{6.02 \times10^{23}}$
Mass of a Fe$(OH)_{2}$ formula unit = 14.93 x $10^{-23}$ g
Mass of a Fe$(OH)_{2}$ formula unit = 1.493 x $10^{-22}$ g
