Question 2.5: Writing the Formula from the Name of an Ionic Compound Write...
Writing the Formula from the Name of an Ionic Compound
Write formulas for the following compounds: a. iron(II) phosphate, b. titanium(IV) oxide.
PROBLEM STRATEGY
From the name of the compound, obtain the name of the ions, then write the formulas of the ions. Finally, use the method of Example 2.3 to obtain the formula of the compound from the formulas of the ions.
a. Iron(II) phosphate contains the iron(II) ion, Fe^{2+}, and the phosphate ion, PO_4^{3-}. (You will need to have memorized the formula of the phosphate ion, or have access to Table 2.6.) Once you know the formulas of the ions, you use the method of Example 2.3 to obtain the formula. The formula is Fe_3(PO_4)_2.
b. Titanium(IV) oxide is composed of titanium(IV) ions, Ti^{4+}, and oxide ions, O^{2-}. The formula of titanium(IV) oxide is TiO_2.
ANSWER CHECK
Whenever you have to write the formula of a compound from its name, make sure that the formula you have written will result in the correct name.
Table 2.6
| Some Common Polyatomic Ions | |||
| Name | Formula | Name | Formula |
| Mercury(I) or mercurous | Hg_2^{2+} | Nitrite | NO_2^- |
| Ammonium | NH_4^+ | Nitrate | NO_3^- |
| Cyanide | CN^- | Hydroxide | OH^- |
| Carbonate | CO_3^{2-} | Peroxide | O_2^{2-} |
| Hydrogen carbonate (or bicarbonate) |
HCO_3^- | Phosphate | PO_4^{3-} |
| Acetate | C_2H_3O_2^- | Monohydrogen phosphate | HPO_4^{2-} |
| Oxalate | C_2O_4^{2-} | Dihydrogen phosphate | H_2PO_4^- |
| Hypochlorite | ClO^- | Sulfite | SO_3^{2-} |
| Chlorite | ClO_2^- | Sulfate | SO_4^{2-} |
| Chlorate | ClO_3^- | Hydrogen sulfite (or bisulfite) |
HSO_3^- |
| Perchlorate | ClO_4^- | Hydrogen sulfate (or bisulfate) |
HSO_4^- |
| Chromate | CrO_4^{2-} | Thiosulfate | S_2O_3^{2-} |
| Dichromate | Cr_2O_7^{2-} | ||
| Permanganate | MnO_4^- | ||