Share
Chemical Formula Writing: Balancing Cation and Anion Charges
Published on March 20, 2026
Other
Determine the neutral chemical formulas formed by combining various metal cations (like Hg2+, Cr6+, Cr4+) with polyatomic anions (like C2O42-, PO43-, SO32-) using charge balancing principles.
Question
Answer
The problem asks for the chemical formula of the compound formed when the given ions combine. To form a neutral compound, the total positive charge from the cations must balance the total negative charge from the anions. This is achieved by using the least common multiple (LCM) of the absolute values of the charges to determine the subscripts (the criss-cross method).
Here are the step-by-step solutions for each part:
a)
-
Identify the charges:
- Cation:
, Charge - Anion:
, Charge (Oxalate ion)
- Cation:
-
Balance the charges: The magnitude of the charges is
and . The LCM of 2 and 2 is 2. - We need
units of and units of such that . - The simplest ratio is
and .
- We need
-
Write the formula:
- The formula is
. - Formula:
- The formula is
b)
-
Identify the charges:
- Cation:
, Charge - Anion:
, Charge (Phosphate ion)
- Cation:
-
Balance the charges: The magnitude of the charges is
and . The LCM of 2 and 3 is 6. - We need
units of and units of such that . - Using the criss-cross method:
and . - Total positive charge:
- Total negative charge:
- Total positive charge:
- We need
-
Write the formula:
- We need 3 units of the
cation group and 2 units of the anion group. Since the anion is polyatomic, we use parentheses for the subscript 2. - Formula:
- Formula:
- We need 3 units of the
c)
-
Identify the charges:
- Cation:
, Charge - Anion:
, Charge (Oxalate ion)
- Cation:
-
Balance the charges: The magnitude of the charges is
and . The LCM of 6 and 2 is 6. - We need
units of and units of such that . - Using the criss-cross method:
and . We simplify the ratio to . - Alternatively, the ratio of charges (6:2) simplifies to 3:1. So we need 1
ion for every 3 ions. - Check:
.
- Alternatively, the ratio of charges (6:2) simplifies to 3:1. So we need 1
- We need
-
Write the formula:
- We need 1
ion and 3 groups. - Formula:
- We need 1
d)
-
Identify the charges:
- Cation:
, Charge - Anion:
, Charge (Sulfite ion)
- Cation:
-
Balance the charges: The magnitude of the charges is
and . The LCM of 4 and 2 is 4. - We need
units of and units of such that . - The ratio of charges is
, which simplifies to . - We need 1 unit of
for every 2 units of ions. - Check:
.
- Check:
- We need
-
Write the formula:
- We need 1
ion and 2 groups. - Formula:
- We need 1
The final formulas are:
a)
b)
c)
d)
a)
b)
c)
d)