Question

Calculate the number of gram-atoms in a sample of lead (atomic weight $207$ ) weighing $100$ grams?
(A) $0.4831$
(B) $0.24$
(C) $4.8$
(D) $0.48$

Answer 1

Hint : Here, in the question, a confusing term is given i.e. gram-atoms, so first we will understand this term, and it is only given to confuse us. So, gram-atoms is nothing but it simply means number of moles of the given sample of the lead.

Complete Step By Step Answer:
So, as we learnt above, by gram-atoms actually they are asking the number of moles in a sample of lease weighing $100$ grams.
So, let’s recall the definition or meaning of the number of moles.
Therefore, a mole is a measure or the base unit for the amount of substance present in the given sample.
In other terms, the number of moles can be defined as the – weight of the given sample atom divided by the molar mass of that molecule of which we have to calculate the number of moles.
So, writing it in the form of formula, we will get:
Number of moles $= \dfrac{{weight}}{{Molar{\text{ mass}}}}$
$\Rightarrow$ $n = \dfrac{w}{M}$
Thus, in the question we are given:
$W = 100$
$M = 207$
Now, put these values in our above formula, and we will get:
$n = \dfrac{{100}}{{207}}$
$\Rightarrow$ $n = 0.4831$
Hence, the number of moles is, $n = 0.4831$
Thus the correct answer is option A. i.e. $0.4831$ Moles
Therefore, $0.4831$ of gram-atoms are present in a sample of lead (atomic weight $207$ ) weighing $100$ grams.

Note :
Number of moles or moles is a very useful quantity as it helps in the determination of the amount of substance in the sample. In the general term one mole is equal to the $6.022 \times {10^{23}}$ , a constant value, which is also known as Avogadro’s constant. And the measurement is applicable for any species like atoms, molecules, ions, electrons, protons etc.