Question

Find the formula unit mass of: (a) NaCl (b) FeO (c) $NaHC{{O}_{3}}$(d)$CuS{{O}_{4}}$
What are polyatomic ions? Give examples.

Answer 1

Hint: Formula unit mass of any compound is the addition of the atomic masses of all the atoms present in the compound multiplied with the individual quantity of the atoms. Ions that have more than two atoms are polyatomic.

Complete answer:
We have been given to find the formula units masses of:
(a)NaCl: the mass of Na is 23 u and that of Cl is 35.4 u, so,
Formula unit mass of NaCl = 23u + 35.4u = 58.4 amu
(b) FeO: mass of Fe is 55.8u, and that of O is 16u, so,
Formula unit mass of FeO = 55.8u + 16u = 71.8 amu
(c) $NaHC{{O}_{3}}$: mass of Na is 23u, H is 1u, C is 12u, O is 16u, so,
Formula unit mass of $NaHC{{O}_{3}}$= 23u + 1u + 12u + 3$\times $ 16u
Formula unit mass of $NaHC{{O}_{3}}$= 84 amu
(d) $CuS{{O}_{4}}$: mass of Cu is 63.5u, S is 32u, O is 16u, so,
Formula unit mass of $CuS{{O}_{4}}$= 63.5u + 32u + 4$\times $ 16u
Formula unit mass of $CuS{{O}_{4}}$= 159.5 amu
Polyatomic ions are species that contain more than one atom. The examples of polyatomic ions are, $S{{O}_{4}}^{2-}$ , sulphate ion, $N{{O}_{3}}^{-}$, nitrate ion, $P{{O}_{4}}^{3-}$ phosphate ion, etc.

Note:
An amu is the unit of atomic mass unit. This unit is the measure of the mass of any atom. other units include gram atomic mass, that means the mass is in gram. Monatomic ions have only one atom, diatomic ions have only 2 atoms.