Formula Writing Chemistry Example 3

Follow the full solution, then compare it with the other examples linked below.

Example 3

medium
Write the correct chemical formulas for: (a) iron(III) sulfate, (b) ammonium carbonate.

Solution

  1. 1
    (a) Iron(III) is Fe3+\text{Fe}^{3+}, sulfate is SO42−\text{SO}_4^{2-}. Crisscross: Fe2(SO4)3\text{Fe}_2(\text{SO}_4)_3. Check: 2(+3)+3(−2)=02(+3) + 3(-2) = 0.
  2. 2
    (b) Ammonium is NH4+\text{NH}_4^+, carbonate is CO32−\text{CO}_3^{2-}. Crisscross: (NH4)2CO3(\text{NH}_4)_2\text{CO}_3. Check: 2(+1)+(−2)=02(+1) + (-2) = 0.

Answer

(a) Fe2(SO4)3(b) (NH4)2CO3\text{(a) Fe}_2(\text{SO}_4)_3\quad \text{(b) (NH}_4)_2\text{CO}_3
When both the cation and anion are polyatomic, use parentheses around each one that has a subscript greater than 1. Roman numerals in the name (like III) indicate the charge of the metal cation.

About Formula Writing

The systematic process of combining element symbols and numerical subscripts to represent the exact composition of a chemical compound, ensuring that the total positive charge.

Learn more about Formula Writing →

More Formula Writing Examples

Example 1 easy

Write the chemical formula for aluminum chloride using the charges of the ions: [formula] and [formu

Example 2 medium

Write the chemical formula for calcium phosphate using the crisscross method. Calcium forms [formula

Example 4 hard

A student writes the formula for magnesium nitride as [formula]. Explain why this is incorrect and d

← All Formula Writing Examples Formula Writing Concept