Question

What is formula mass of $Ba{{(HS{{O}_{3}})}_{2}}$?
a.) 299
b.) 250
c.) 290
d.) 260

Answer 1

Atomic mass of Barium is 137.32, atomic mass of hydrogen is 1, atomic mass of oxygen is 16 , atomic mass of Sulphur is 32.06. Formula mass of a molecule is the sum of atomic weights of atoms in the empirical formula.

Complete step by step answer:
-Empirical formula is the simplest whole number ratio of various atoms present in a compound.
-Molecular formula shows exact number of different types of atoms present in a molecule of a compound.
- Formula mass of a molecule is the sum of atomic weights of atoms in the empirical formula.
-For a covalent substance, formula represents number and types of atoms in a single molecule of substance.
-For an ionic substance, formula mass is obtained by adding average atomic masses of all atoms present in a compound's formula.
-Main difference between formula mass and molecular mass is that the formula mass is calculated adding masses in simplest formula whereas molecular mass is calculated using actual numbers of atoms present in a molecule.
-Hence formula mass of $Ba{{(HS{{O}_{3}})}_{2}}$ can be calculated as follows:
=1(atomic mass of barium) + 2 (atomic mass of hydrogen) + 2 (atomic mass of Sulphur) +6 (atomic mass of Sulphur)
=1 (137) +2 (1) +2(32) +6 (16)
=299
Hence, formula mass of $Ba{{(HS{{O}_{3}})}_{2}}$ is So, the correct answer is “Option A”.

Note: formula mass of covalent compound is same as molecular mass but for ionic compound it is sum of mass of all atoms in simplest formula. Empirical formulas and simplest formulas are not the same.
-Empirical formula is the simplest whole number ratio of various atoms present in a compound.