Ammonium iron(III) sulfate (also known as ferric ammonium alum) is a hydrated, water-soluble mineral with a relative formula mass of 482.0.
The formula of ammonium iron(III) sulfate can be represented as M⋅xH2O\text{M}\cdot x\text{H}_2\text{O}M⋅xH2O, where M\text{M}M represents all the ions present.
Table 1 shows its composition by mass.
Table 1
| Element | % by mass |
|---|---|
| N\text{N}N | 2.90 |
| H\text{H}H | 5.81 |
| Fe\text{Fe}Fe | 11.58 |
| S\text{S}S | 13.32 |
| O\text{O}O | 66.39 |
In an analysis, it is found that the mineral contains the ions NH4+\text{NH}_4^+NH4+, Fe3+\text{Fe}^{3+}Fe3+, and SO42−\text{SO}_4^{2-}SO42−.
Calculate the empirical formula of ammonium iron(III) sulfate and the value of x x\,x in M⋅xH2O\text{M}\cdot x\text{H}_2\text{O}M⋅xH2O.
Describe the chemical tests (with their reagents and observations), including ionic equations, that would confirm the identities of the three ions present.
