Question

If a dentist used 30mg of amalgam silver in his work, whose silver content is 72% (by mass), the number of silver atoms your customer received in your dental arcade is approximately?

Answer 1

First we will work in equal mass units, that is:
We will transform 30 mg into g:

1 g ---------- 1000 mg
X g ---------- 30 mg

X = 30/1000

X = 0.03 g

Now calculate the mass of silver in the amalgam:

0.03 g ----------- 100%
And ------------------ 72%

Y = 0.03. 72/100

Y = 2.16 / 100

Y = 0.0216 g Ag or 2.16.10 g g

Finally the calculation of silver atoms received by the customer:

Silver atomic mass (Ag) = 108 u

So :

1 mol Ag -------- 108g
X mol Ag -------- 2.16.10⁻²

X = 2.10⁻² / 108

X = 2.10⁻⁴ mols

1 mol --------------------- 6.02.10²³ atoms
2.10⁻⁴ mols ------------- and

Y = 2.10⁻⁴ (6.02.10²³)

Y = 12.0.10¹⁹ Ag atoms