Question

The arsenate ion has the formula \(\mathrm{AsO}_{4}{ }^{3-}\). Write the formula of the corresponding acid that contains this anion. (Hint: The cation for the corresponding acid is \(\mathrm{H}^{+} .\) )

Short answer

The formula of the corresponding acid is \(\mathrm{H}_{3}\mathrm{AsO}_{4}\).

Step-by-step solution

Identify the Anion

The given anion is \(\mathrm{AsO}_{4}^{3-}\). It indicates that the arsenate ion carries a charge of \(-3\).

Determine the Required Cations

To create a neutral compound, the total positive charges must balance the negative charge of the anion. Since each hydrogen ion \(\mathrm{H}^{+}\) carries a \(+1\) charge, we need \(3\) hydrogen ions to balance the \(-3\) charge of \(\mathrm{AsO}_{4}^{3-}\).

Construct the Acid Formula

Combine three \(\mathrm{H}^{+}\) ions with one \(\mathrm{AsO}_{4}^{3-}\) ion to form the corresponding acid. This results in the formula \(\mathrm{H}_{3}\mathrm{AsO}_{4}\).

Key concepts

Arsenate Ion

The arsenate ion, denoted as \( \mathrm{AsO}_{4}^{3-} \), is a polyatomic ion composed of one arsenic atom and four oxygen atoms. It carries a total negative charge of \(-3\). This ion is found in various chemical compounds and is essential in the study of acid-base chemistry, particularly when dealing with the formation of certain acids.

Understanding the charge of the arsenate ion is crucial because it determines how it will interact with other ions to form a neutral compound. In acid-base reactions, the arsenate ion combines with positively charged ions to create an overall balanced charge. Recognizing the structure and charge of the arsenate ion helps in identifying the appropriate cations needed to balance its charge in a compound.

Anion Identification

Anion identification is a fundamental process in chemistry, where specific ions are recognized based on their chemical formula and charge. In this exercise, the anion in focus is the arsenate ion, labeled as \( \mathrm{AsO}_{4}^{3-} \).

The first step in identifying anions is to look at their formula, which provides clues about the number of atoms and the charge of the ion. For arsenate, the formula shows one arsenic atom bonded with four oxygens, collectively holding a total negative charge of \(-3\).

Accurate identification of anions like arsenate is integral in predicting their reactivity and the compounds they form, specifically for constructing acids or salts. Recognizing the overall charge also aids in determining the suitable cations that must be paired with the anion to achieve neutrality in a chemical formula.

Acid Formula Determination

Determining the formula for an acid involves combining the appropriate cations and anions to result in a neutral compound. For the arsenate ion \( \mathrm{AsO}_{4}^{3-} \), the corresponding acid is formed by adding hydrogen ions \( \mathrm{H}^{+} \).

Since the arsenate ion carries a \(-3\) charge, three hydrogen ions, each with a \(+1\) charge, are required to balance the ion's charge. Combining these ions results in the formation of the neutral compound, phosphoric acid, with the formula \( \mathrm{H}_{3}\mathrm{AsO}_{4} \).

This process illustrates the principles of charge balance and stoichiometry, where the number of ions must be adjusted to ensure that the resulting chemical formula is electrically neutral. Understanding such principles is essential for acid-base chemistry, aiding in the prediction and creation of a wide variety of chemical compounds.