Question

The molecular weight of a Hydrogen atom _____ is kg.
(A) 1.79$ \times {10^{ - 27}}$Kg
(B) 1.73$ \times {10^{ - 27}}$Kg
(C) 1.68$ \times {10^{ - 27}}$Kg
(D) None of these

Answer 1

Hint: We know that the hydrogen atom is the simplest atom there is with only one electron, one proton and zero neutrons. Molecular weight is the mass of a molecule of a substance, it can also be called molecular mass and is denoted by amu.

Complete step-by-step solution:The fact that hydrogen is the first element in the modern periodic table is well known to us, with the atomic number 1 and according to the very periodic table, the mass of a hydrogen atom is 1.00794 amu, but we have to get this value in terms of Kg, as all the options are given in kilograms.
Now, to convert 1 amu into kg we have to multiple 1.67377 $ \times {10^{ - 27}}$ with 1 and this will give 1.67377 $ \times {10^{ - 27}}$ kg
$ \Rightarrow $ 1 amu = 1.67377 $ \times {10^{ - 27}}$ kg
$ \Rightarrow $ 1.00794 amu = 1.00794 $ \times $ 1.67377 $ \times {10^{ - 27}}$
$ \Rightarrow $ 1.00794 amu = 1.68 $ \times {10^{ - 27}}$ kg
Therefore, the molecular weight of hydrogen is 1.68 $ \times {10^{ - 27}}$ kg.

Additional information: The hydrogen atom has two more forms, these are known as isotopes of hydrogen (i.e., having the same atomic number but a different mass number). These are:
i. Deuterium
ii. Tritium

Hence, the correct answer is option is (C) i.e., 1.68 $ \times {10^{ - 27}}$ kg.

Note: The two terms often get confused between are molar mass and molecular mass/ molecular weight. Where molar mass is the mass of the one mole of a particular substance and is represented as g/mol, the molecular weights are denoted by AMU (atomic mass unit), it is the mass of a molecule of a substance.