Question

(a) Calculate the gram molecular mass of water from the values of gram atomic mass of hydrogen and of oxygen.
Gram atomic mass of hydrogen=1g
Gram atomic mass of oxygen=16g
(b) Atoms and molecules are the building blocks of matter. list out any three differences between them.

Answer 1

Hint: Molecular mass is the mass of a given molecule, Simply, we can say that it is the number equal to the sum of the atomic masses of the atoms in a molecule. it is measured in Daltons. The molecular formula of water is ${{H}_{2}}O$.

Complete step by step solution:
-Lets first solve the question (a):
We know that the molecular formula of water is ${{H}_{2}}O$.
And we know that gram atomic mass of hydrogen=1g. And gram atomic mass of oxygen=16g,
So, here we have two hydrogens and one oxygen, therefore gram molecular mass of water would be,
\[\begin{align}
  & {{H}_{2}}O \\
 & =2\times 1g+16g \\
 & =18g \\
\end{align}\]
Hence, we can conclude that gram molecular mass of water is 18g.
-Now, for question (b) we have to list the differences between atoms and molecules.

Atoms	Molecules
(a) Atoms are the smallest particle in an element and this has the property of an element.	(a) Molecules are formed when two or more atoms are combined together.
(b) Atoms can’t be broken down into further pieces	(b) Molecules can be broken down into further pieces.
(c) Atoms can’t be stable by itself because to be stable, atoms need sufficient electrons. And it gets sufficient electrons by sharing electrons with other atoms and hence forms molecules and gets stabilised.	(c) Molecules can get stabilised by itself.

Hence, the differences between atoms and molecules are cleared from the above table.
Additional Information:
- We know that the chemical and physical property of any state of matter is entirely dependent on their constituents. Therefore, it is necessary to calculate the mass of an atom so that we can calculate the mass of molecules also.
- the atomic and molecular masses can be represented in terms of ‘Mole concept’. We can define mole as a collection of atoms whose mass is equal to the atomic mass in grams.
- It is found that the number of atoms in a mole is $6.02\times {{10}^{23}}$. This number is known as Avogadro’s number.

Note: - We must be careful while finding the total molecular mass, from molecular formula. For example, in case of water we have multiplied the given molecular mass of hydrogen with the subscript 2. Here, one can make a mistake of adding subscript with the molecular mass of hydrogen.
- One must remember that an atom is the smallest particle in an element and molecules are formed when two or more atoms bond together.