Answer :
To solve this question, we need to follow 2 steps:
Step 1 - Transform atoms into moles, using the avogadro's constant: 6.02214086 × 10^23 mol^-1
Step 2 - Transform moles into grams, using the molar mass of the compound and the following formula: mass = moles x molar mass
a) Here we have 4.25 x 10^24 atoms of nitrogen - N.
Step 1:
6.02214086 × 10^23 atoms ---- 1 mol
4.25 x 10^24 atoms of nitrogen ---- x moles of nitrogen
6.02214086 × 10^23 x = 4.25 x 10^24
x = 4.25 x 10^24/6.02214086 × 10^23
x = 7.06 moles of nitrogen
Step 2:
The molar mass of nitrogen is 14 g/mol.
Moles = 7.06
mass of nitrogen = 7.06 x 14
mass of nitrogen = 98.8 g
Answer a) mass of nitrogen = 98.8 g
b) We follow the same steps. Here we have 1.75 x 10^23 atoms of Pb.
Step 1:
6.02214086 × 10^23 atoms ---- 1 mol
1.75 x 10^23 atoms of Pb---- x moles of Pb
6.02214086 × 10^23 x = 1.75 x 10^23
x = 1.75 x 10^23 /6.02214086 × 10^23
x = 0.291 atoms of Pb
Step 2:
The molar mass of Pb is 207.2 g/mol.
moles = 0.291
mass of Pb = 0.291 x 207.2
mass of Pb = 60.2 g
Answer: b) mass of Pb = 60.2 g
c) Here we have 8.45 x 10^23 molecules of CH4.
Step 1:
6.02214086 × 10^23 molecules --- 1 mol
8.45 x 10^23 molecules of CH4---- x moles of CH4
6.02214086 × 10^23 x = 8.45 x 10^23
x = 8.45 x 10^23 /6.02214086 × 10^23
x = 1.403 moles of CH4
Step 2:
The molar mass of C is 12 g/mol and of H is 1 g/mol. We need to calculate the molar mass of CH4:
(1x12) + (4x1) = 16 g/mol
moles = 1.403 moles of CH4
mass of CH4 = 1.403 x 16
mass of CH4 = 22.5 g
Answer: c) mass of CH4 = 22.5 g