Question

Write the formula for (a) chromic acid, (b) carbonic acid, and (c) oxalic acid.

Short answer

The formulas are: (a) H2CrO4, (b) H2CO3, (c) H2C2O4.

Step-by-step solution

Identify the Composition of Chromic Acid

Chromic acid is a combination of chromium in its hexavalent form, Cr(VI), and the hydroxide ion. The formula can be determined by balancing the charges of chromium and the hydroxide ions.

Write the Formula for Chromic Acid

To balance the charges, we combine one CrO3 unit with two hydroxide ions (OH-) to yield H2CrO4, which is the formula for chromic acid.

Identify the Composition of Carbonic Acid

Carbonic acid is formed by the combination of carbon dioxide (CO2) and water (H2O).

Write the Formula for Carbonic Acid

The reaction of carbon dioxide with water yields carbonic acid. Thus, the formula is H2CO3.

Identify the Composition of Oxalic Acid

Oxalic acid is formed by two carboxylic acid groups (-COOH), derived from oxalate, which contains two carbons.

Write the Formula for Oxalic Acid

Each carboxylic group has a -1 charge and there are two hydrogen ions, so the balanced formula for oxalic acid is H2C2O4.

Key concepts

Chromic Acid Formula

Understanding the formula of chromic acid requires a basic knowledge of chemical composition and valency. Chromic acid, often represented as H₂CrO₄, is a somewhat tricky compound because it involves the hexavalent form of chromium, Cr(VI). Here's a simple breakdown:

The base unit for chromic acid is CrO₃, which is chromium trioxide. When this reacts with water (H₂O), it yields chromic acid. In terms of charge, CrO₃ combines with the hydroxide ion (OH^-) to balance the positive and negative charges effectively. The result is the stable, balanced acid formula, H₂CrO₄.

Remember that the subscript numbers indicate the number of atoms in the molecule. So in H₂CrO₄, there are two hydrogen atoms, one chromium atom, and four oxygen atoms that come together to form chromic acid.

Carbonic Acid Composition

Carbonic acid, expressed with the formula H₂CO₃, is quite fundamental in chemistry, especially in physiological processes and the carbon cycle. But what exactly makes up carbonic acid? At its core, the molecule is composed of carbon dioxide (CO₂) and water (H₂O).

When these two react, they form H₂CO₃, which is an important compound in our body for maintaining pH balance and in the environment as part of the process of carbonation. Composition-wise, the formula tells us there are two hydrogen atoms, one carbon atom, and three oxygen atoms. The structure of carbonic acid makes it a very weak and unstable acid, which decomposes easily into water and carbon dioxide.

Oxalic Acid Structure

Getting accustomed to the structure of oxalic acid is a foundational chemistry task. Oxalic acid has the formula H₂C₂O₄, which can be a bit puzzling at first glance due to its multiple oxygen atoms. To understand it, let’s break it down:

H₂C₂O₄ is comprised of two carboxylic acid (-COOH) groups, each one contributing a -COO^- and a hydrogen ion (H⁺). Essentially, it's as if two carboxylic acid molecules come together to form oxalic acid. What's interesting is that oxalic acid is a dibasic acid, which means it has two hydrogen ions that can dissociate in solution. In its solid form, oxalic acid exists as a dihydrate, with two additional water molecules, hinted by the '.2H₂O' that is sometimes added to the molecular formula. This structure makes oxalic acid quite reactive, especially in cleaning applications to remove rust and as a bleaching agent.