Question

Number of atoms in 560 g of Fe (atomic mass = 56 u) is

• A. Twice that of 70 g N
• B. Half that of 20 g H
• C. Equal to that of 70 g N
• D. None of these

Answer 1

Answer: (A)

Twice that of 70 g N

Given, mass of Fe $=560g$

Atomic mass of Fe $=56u$

So, molar mass of Fe $=56gmo{l}^{-1}$

Number of moles $=\frac{Mass}{MolarMass}$ $=\frac{560}{56}$ $=10$

Number of atoms in 560 g Fe $=Numberofmoles\times Avogadronumber$ $=10\times 6.022\times {10}^{23}$

Next, let's find the number of atoms in 70 g N

Given, mass of N $=70g$

Atomic mass of N$=14u$

So, molar mass of N $=14gmo{l}^{-1}$

Number of moles $=\frac{Mass}{MolarMass}$ $=\frac{70}{14}$ $=5$

Number of atoms in 70 g N$=Numberofmoles\times Avogadronumber$ $=5\times 6.022\times {10}^{23}$

Comparing number of atoms in 560 g Fe and 70 g N:

Number of atoms in 560 g Fe $=10\times 6.022\times {10}^{23}$

Number of atoms in 70 g N $=5\times 6.022\times {10}^{23}$

So, number of atoms in 560 g Fe = Twice the number of atoms in 70 g N