Taking into account that 1 mol of Pb has a mass of 207.2 g, the mass of 0.400 moles of Pb is 82.92 grams.
The rule of three is a tool that allows the resolution of problems related to the proportionality between three known values and a fourth that is unknown.
If the relationship between the magnitudes is direct, that is, when one magnitude increases, so does the other (or when one magnitude decreases, so does the other), the direct rule of three must be applied.
To solve a direct rule of three, the following formula must be followed, where a, b and c are known values and x is the unknown value to calculate:
a ⇒ b
c ⇒ x
So: [tex]x=\frac{cxb}{a}[/tex]
In this case, the rule of three can be applied as follows: if 1 mole of Pb contains 207.2 grams, 0.400 moles contain how much mass?
1 mole ⇒ 207.3 grams
0.400 moles ⇒ x
So:
[tex]mass=\frac{0.400 moles*207.3 grams}{1 mole}[/tex]
mass= 82.92 grams
In summary, the mass of 0.400 moles of Pb is 82.92 grams.
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