Question

Write the formula for each of the following carboncontaining polyatomic ions, including the overall charge of the ion. a. carbonate b. hydrogen carbonate c. acetate d. cyanide

Short answer

a. Carbonate: \(CO_3^{2-}\) b. Hydrogen carbonate: \(HCO_3^-\) c. Acetate: \(CH_3COO^-\) or \(C_2H_3O_2^-\) d. Cyanide: \(CN^-\)

Step-by-step solution

a. Carbonate

The carbonate ion consists of one carbon atom bonded with three oxygen atoms. It has a charge of -2. Therefore, the formula for the carbonate ion is CO3^2-.

b. Hydrogen carbonate

The hydrogen carbonate ion (also known as bicarbonate) consists of one hydrogen atom, one carbon atom, and three oxygen atoms. It has a charge of -1. Therefore, the formula for the hydrogen carbonate ion is HCO3^-.

c. Acetate

The acetate ion is formed from one of the simplest organic compounds - acetic acid. It consists of two carbon atoms, three oxygen atoms, and three hydrogen atoms, with an overall charge of -1. Therefore, the formula for the acetate ion is CH3COO^- or C2H3O2^-.

d. Cyanide

The cyanide ion is formed from a carbon atom triple-bonded to a nitrogen atom. It has a charge of -1. Therefore, the formula for the cyanide ion is CN^-.

Key concepts

The Carbonate Ion (CO3^2-)

Understanding the carbonate ion is fundamental in chemistry, especially in different areas such as geochemistry, biological chemistry, and environmental science. The carbonate ion consists of one carbon atom centrally bonded to three oxygen atoms in a trigonal planar geometry. This ion carries a charge of -2, which is indicated by the superscript in its chemical formula, \( \text{CO}_3^{2-} \).

The presence of carbonate ions in compounds can affect their properties and reactivity. For instance, carbonate compounds can react with acids to produce carbon dioxide, a reaction that is integral to processes like weathering of rocks and cellular respiration.

The Hydrogen Carbonate Ion (HCO3^-)

Also known as the bicarbonate ion, the hydrogen carbonate ion plays a crucial role in the pH buffering system of blood and other biological fluids. This polyatomic ion features one hydrogen atom attached to a carbonate group. Like the carbonate ion, it includes a central carbon atom surrounded by three oxygen atoms, with one of these oxygens also bound to the hydrogen atom. The formula \( \text{HCO}_3^- \) reflects its single negative charge, which is less than that of the carbonate ion.

It’s interesting to note that the hydrogen carbonate ion serves as a transitional form in the conversion of carbon dioxide to carbonate compounds in nature, such as in ocean chemistry where it helps regulate oceanic pH.

The Acetate Ion (CH3COO^- or C2H3O2^-)

The acetate ion is derived from acetic acid, which is the main component of vinegar. It contains two carbon atoms, three hydrogen atoms, and two oxygen atoms. The arrangement consists of a methyl group (\(\text{CH}_3\)) attached to a carboxylate group (\(\text{COO}^-\)). Acetate has a single negative charge indicated by the minus sign in the formulas \( \text{CH}_3\text{COO}^- \) or alternatively \( \text{C}_2\text{H}_3\text{O}_2^- \).

Acetate ions are prevalent in biochemistry, particularly in the metabolism of carbohydrates and fats where they serve as a key component of the citric acid cycle.

The Cyanide Ion (CN^-)

Cyanide is a potent ion with a simple structure—one carbon atom triple-bonded to a nitrogen atom, carrying a charge of -1. Its formula is expressed as \( \text{CN}^- \). Despite its infamous toxicity, cyanide has important industrial applications, such as in the mining of precious metals where it's used to extract gold and silver from their ores.

It’s vital for students to understand that the cyanide ion should be handled with extreme care due to its high toxicity, which disrupts cellular respiration. Despite this, cyanide also occurs naturally in certain plants and is metabolized in small amounts within the body.