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+1 vote
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in Some basic concepts in chemistry by (20 points)
edited by

The number of atoms in 4.25 g of NH3 is

(a) 4 x 1023

(b) 2 x 1023

(c) 1 x 1023

(d) 6 x 1023

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1 Answer

+1 vote
by (31.3k points)

The correct answer is (d) 6.023 × 1023

One mole of a chemical entity can be defined as equal to 6.023×1023 particles of that substance, where “particles” can mean “atoms, molecules, and the different subatomic particles”. We shall calculate the moles of the compound given and thus, the number of particles.

Formula Used: \(moles = \frac{mass}{molar\, mass}\)

The molecular weight of ammonia is equal to the sum of the atomic weights of nitrogen and hydrogen atoms = [14+(3×1)]= 17 grams

Hence, 17 grams of ammonia = 6.023×1023 molecules of ammonia.

Therefore, 4.25g of ammonia \(= \frac{6.023 \times 10^{23}}{17} \times 4.25 = 1.505 \times 10^{23}\) molecules of ammonia.

Now each molecule of ammonia has four atoms, one atom of nitrogen and three atoms of hydrogen. Hence, the total number of atoms in 1.505 x 1023 molecules of ammonia

= 4×1.505 × 1023

= 6.023 × 1023 atoms.

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