Question

Write a formula for each acid. (a) phosphoric acid (b) hydrobromic acid (c) sulfurous acid

Short answer

The formulas are: (a) Phosphoric acid - H3PO4, (b) Hydrobromic acid - HBr, (c) Sulfurous acid - H2SO3.

Step-by-step solution

Identify the Anion for Phosphoric Acid

Phosphoric acid is derived from the phosphate anion. In order to write its formula, we must first recognize that the phosphate anion is PO4 with a 3- charge.

Write the Formula for Phosphoric Acid

Phosphoric acid has three hydrogen ions to balance the 3- charge on the phosphate anion. Therefore, the formula for phosphoric acid is H3PO4.

Identify the Anion for Hydrobromic Acid

Hydrobromic acid is a binary acid consisting of hydrogen and a halogen. Here, the bromide anion is involved, which is Br with a 1- charge.

Write the Formula for Hydrobromic Acid

To neutralize the charge of the bromide anion, we need one hydrogen ion. Hence, the formula for hydrobromic acid is HBr.

Identify the Anion for Sulfurous Acid

Sulfurous acid results from the sulfite anion. The sulfite anion is SO3 with a 2- charge.

Write the Formula for Sulfurous Acid

Two hydrogen ions are needed to balance the 2- charge on the sulfite anion. Therefore, the formula for sulfurous acid is H2SO3.

Key concepts

Phosphoric Acid H3PO4

Phosphoric acid is a common acid present in many household cleaners as well as fertilizers. Its chemical formula is written as H3PO4. This formula tells us that one molecule of phosphoric acid consists of three hydrogen atoms (H), one phosphorus atom (P), and four oxygen atoms (O). The subscript numbers in the chemical formula represent the count of each type of atom in the molecule. As noted in the exercise, the anion for phosphoric acid, phosphate, carries a 3- charge. The addition of three positively charged hydrogen ions helps to balance this charge, resulting in a neutral compound.

Hydrobromic Acid HBr

Hydrobromic acid is a strong acid that is highly soluble in water. With the formula HBr, it is composed of a hydrogen atom (H) and a bromine atom (Br). Unlike phosphoric acid, hydrobromic acid is a binary acid, meaning it contains only two elements. In the solution provided, the bromide anion carries a single negative charge, which is balanced by a single positive hydrogen ion. Hydrobromic acid is notable in inorganic chemistry for being one of the strongest mineral acids and is commonly used to prepare bromide salts.

Sulfurous Acid H2SO3

Sulfurous acid, with its chemical formula H2SO3, contains two hydrogen atoms, one sulfur atom, and three oxygen atoms. It is a weak acid and not commonly found in the pure state, but it is often formed when sulfur dioxide gas dissolves in water, which is an important component in acid rain. The anion here is sulfite (SO3) with a 2- charge, and as the problem solution indicated, balancing this with two hydrogen ions results in a stable, neutral molecule.

Chemical Nomenclature

Understanding chemical nomenclature is crucial for writing and communicating chemical formulas accurately. It is a standardized system used by chemists to name substances and describe their composition. The nomenclature takes into account the type of elements present, their quantities, and their arrangement. For acids, the name often reflects the anion they contain, with 'ic' added to the root name of the anion for acids derived from anions ending in 'ate', like 'phosphate' leading to 'phosphoric acid', or a change from 'ide' to 'hydro-' prefix and 'ic' for binary acids, as seen with 'bromide' to 'hydrobromic acid'.

Balancing Charges in Compounds

The principle of balancing charges in compounds is fundamental in writing correct chemical formulas. Atoms combine to form compounds by transferring or sharing electrons, creating ions with positive or negative charges. Compounds are stable when the total charges of the constituent ions balance to zero. This is achieved by adjusting the numbers of each type of ion so their charges sum to neutrality; for instance, the 3- charge of phosphate is balanced by three H+ ions in phosphoric acid. It's critical for students to first discern the charge on anions and then determine the required number of cations to achieve a balanced, electrically neutral molecule.