How do you derive an acid's formula from its name?

Answer 1

An acid is any compound that contains a H+ (hydrogen) ion. All acids' formulas begin with H (hydrogen) and all acids are named based on their anions (remember that compound names and formulas are in the format cation + anion).

To obtain the formula of an acid when given the name, follow these steps accordingly. The following steps involves removing prefixes and suffixes, resulting in identifying the name of the anion.

I. IDENTIFYING THE ANION

If the prefix "hydro-" is present:

1. Drop the prefix "hydro-" and "-ic acid".

2. Replace "-ic acid" with the suffix "-ide"

Now if the prefix "hydro" is not present, look at the end of the name.

If the name ends with "-ic acid":

1. Drop "-ic acid".

2. Replace "-ic acid" with the suffix "-ate".

If the name ends with "-ous acid":

1. Drop "-ous acid".

2. Replace "-ous acid" with "-ite".

II. IDENTIFYING THE FORMULA

As stated earlier, the steps listed above were to identify the name of the anion. Now that the anion has been identified, we can give the formula. Remember how acids have H+ ions and a compound? Given that statement, it can be said that all acids have the following formula format:

H+ + Anion Compound (Cation + Anion)

When writing the equation, write the formula and charge for both the hydrogen ion (cation) and the anion in the format given above. When writing the actual formula, add the number of H atoms according to the charge of the anion. Keep in mind that in the formula, the charges of all atoms must equal to zero.

ex. Hydrocyanic acid (prefix "hydro-" is present, ends with "-ic acid")

1. Drop "hydro-" and "-ic acid".

Cyan

2. Replace "-ic acid" with the suffix "-ide"

Result: Cyanide, CN-

3. Write the equation.

H+ + CN-

4. Since there is a -1 charge on cyanide, the formula is written as: HCN

Hydrocyanic acid: HCN

ex. Boric acid (prefix "hydro-" is absent, ends with "-ic acid").

1. Drop "-ic acid".

Bor

2. Replace "-ic acid" with the suffix "-ate".

Result: Borate, BO3-3

3. Write the equation.

H+ + BO3-3

4. Since the charge of borate is -3, the formula is written as: H3BO3

Boric Acid: H3BO3

Ex. Chlorous acid (prefix "hydro-" is absent, ends with "-ous acid")

1. Drop "-ous acid".

Chlor

2. Replace "-ous acid" with "-ite".

Result: Chlorite, ClO2-1

3. Write the equation.

H+ + ClO2-

4. Since the charge of chlorite is -1, the formula is written as: HClO2.

Chlorous acid: HClO2

To summarize:

Acid formula format: H+ + Anion Compound (Cation + Anion)

1. Identify anion by removing the prefix (if applicable) and changing the suffix accordingly.

2. Identify the formula by writing the equation and determining number of hydrogen atoms in the acid per the anion's charge.

Answer 2

To derive an acid's formula from its name, identify the type of acid based on its ending (-ic acid for anion ending in -ate, and -ous acid for anion ending in -ite), then determine the charge of the anion. Use this information to balance the charges in the formula of the acid. For example, sulfuric acid (H2SO4) has an -ate anion (sulfate) with a charge of -2, requiring two hydrogen ions (each with a +1 charge) to balance the charges.