Question

Calculate the relative atomic mass of zinc sulphate.
\[\left[ {Zn = 65;{\text{ }}S = 32;{\text{ }}O = 16} \right]\]

Answer 1

Hint: An atom comprises a nucleus having neutrons and protons which are surrounded by electrons in orbits. Number of protons (atomic number) can be considered to be equal to the total number of electrons in a neutral atom (denoted as Z). Whereas, the summation of the number of neutrons and number of protons equals the mass number of an atom or atomic mass (denoted as M).

Complete answer:
- The scale of relative atomic mass is now based upon an isotope of carbon, i.e. carbon-12. So, we can say that the relative atomic mass is equal to the average mass of all atoms present in an element in comparison to the 1/12th of the mass of a C-12 atom.
- Owing to the presence of more neutrons (compared to protons) in the nucleus, relative atomic mass is generally at least double of the atomic number. It should also be noted that the numerical difference between atomic number and relative atomic mass increases with the increasing atomic number.
- In the present question, we are not given the different isotopic masses and % abundance of the elements so we will roughly calculate the relative atomic mass of zinc sulphate by adding the atomic mass of each atom as follows:
- Zinc sulphate has the chemical formula $ZnS{O_4}$which contains 1 atom of \[Zn\], 1 atom of \[S\] and 4 atoms of \[O\].
The relative atomic mass = $(1 \times 65) + (1 \times 32) + (4 \times 16) = 161$

Hence, the relative atomic mass of zinc sulphate of 161.

Note:
In order to calculate the exact relative atomic mass, different isotopic masses of the same element must be taken into account along with their % abundance in the element.