Question

Which among the following is the heaviest?
A. One mole of oxygen
B. One molecular of sulphur trioxide
C. 100 amu of uranium
D. 44g of carbon dioxide

Answer 1

Hint: To solve this question find the weight of an individual molecule and then check which of the options is correct, the molecule which has greater weight will be the heaviest among them. To find the weight you can use any formula with respect to the requirement of the option.

Complete step by step answer:
From your chemistry lessons you have learned about the molecular mass, amu, Avogadro number and about the moles. Using these concepts we are going to solve this question. Among all of the given options the element which will have the greater mass or weight will be the heaviest.
Let, us check the options one by one,
(A). one mole of oxygen
To find the weight we will use the formula,

\[no.\,of\,moles=\dfrac{given\,mass}{molar\,mass}\]
Here, we have to find the weight or mass, so the formula will be,

\[given\,mass=no.\,\,of\,moles\times molar\,mass\]
Now, the no. of moles is given as 1, and the molecular mass of oxygen $({{O}_{2}})$ is 16
Therefore, $given\,mass=1\times 16=16g$

(B). One molecular of sulphur trioxide $(S{{O}_{3}})$
To calculate the weight we will use Avogadro number$(6.022\times {{10}^{23}})$
Molecular mass of $S{{O}_{3}}=32+16\times 3=80g$
\[6.022\times {{10}^{23}}\] molecules of \[S{{O}_{3}}\] weigh 80 g
then, 1 molecule of $S{{O}_{3}}$ will weight = $\dfrac{80}{6.022\times {{10}^{-23}}}=80\times 6.022\times {{10}^{-23}}=4.8\times {{10}^{-21}}$
Thus the weight of $S{{O}_{3}}$ is $4.8\times {{10}^{-21}}$.

(C) 100 amu of uranium
Here, 1amu= $1.66\times {{10}^{-24}}g$
Thus 100 amu of U = $100\times 1.66\times {{10}^{-24}}=1.66\times {{10}^{-22}}g$

(D) 44g of $C{{O}_{2}}$
44g of $C{{O}_{2}}$= 1 mole = 44g
Hence, the heaviest among all of them is $C{{O}_{2}}$.
So, the correct answer is “Option D”.

Note: To find the weight of an element there are many ways. Atomic mass unit (amu) is defined as the 1/12 mass of the atom of carbon-12. In the carbon-12 atom there are six neutrons and six protons. And 1 amu is the average of neutron and proton rest mass. 1 amu = $1.66\times {{10}^{-24}}g$