Problem 86 - Chemistry The Molecular Science

Question

Double-acting baking powder contains two salts, sodium hydrogen carbonate and potassium dihydrogen phosphate, whose anions react in water to form \(\mathrm{CO}_{2}\) gas. Write a balanced chemical equation for the reaction. Which anion is the acid and which is the base?

Step-by-Step Solution

Answer

The balanced equation is: \(\text{HCO}_3^- + \text{H}_2\text{PO}_4^- \rightarrow \text{H}_3\text{PO}_4 + \text{CO}_2 + \text{H}_2\text{O}\). \(\text{H}_2\text{PO}_4^-\) is the acid, and \(\text{HCO}_3^-\) is the base.

Step 1: Identify the Anions Involved

Sodium hydrogen carbonate contains the anion bicarbonate \((\text{HCO}_3^-)\), while potassium dihydrogen phosphate contains the anion dihydrogen phosphate \((\text{H}_2\text{PO}_4^-)\). These are the reacting anions in the double-acting baking powder.

Step 2: Determine the role of Anions

The bicarbonate ion (\(\text{HCO}_3^-\)) can act as a conjugate base in reactions, while the dihydrogen phosphate ion (\(\text{H}_2\text{PO}_4^-\)) can act as an acid.

Step 3: Write the Reaction Equation

In water, bicarbonate (base) accepts a proton from dihydrogen phosphate (acid), releasing \( ext{CO}_2\) gas. The balanced chemical equation is: \[ \text{HCO}_3^- + \text{H}_2\text{PO}_4^- \rightarrow \text{H}_3\text{PO}_4 + \text{CO}_2 + \text{H}_2\text{O} \]

Step 4: Classify Acid and Base

In the reaction, \(\text{H}_2\text{PO}_4^-\) donates a proton, making it the acid, while \(\text{HCO}_3^-\) accepts a proton, making it the base.

Key Concepts

Acid-Base Reactions

Acid-base reactions are a fascinating part of chemistry that involve a transfer of protons between reactants. These reactions can occur in various systems, including solutions and gases. Typically, an acid donates a proton ( ext{H}^+), whereas a base accepts this proton. For double-acting baking powder, a common household item, this concept plays a vital role in its function. Here, we see the bicarbonate ion ( ext{HCO}_3^-) acting as a base, accepting a proton from the dihydrogen phosphate ion ( ext{H}_2 ext{PO}_4^-) which is acting as an acid. This proton transfer causes the release of carbon dioxide ( ext{CO}_2) gas, which helps baked goods rise. Understanding these interactions helps in predicting the outcome of combining different substances. A key takeaway is always to remember that acids are proton donors and bases are proton acceptors.

Balancing Chemical Equations

Balancing chemical equations is a critical skill in chemistry that ensures mass conservation during a chemical reaction. Every atom on the reactants' side must be accounted for on the products' side. The reaction involving bicarbonate and dihydrogen phosphate in baking powder can be described by a balanced chemical equation.

• Start by writing the chemical formulas of the reactants and products.
• Ensure the number of each type of atom is the same on both sides of the equation.
• Adjust coefficients as needed to balance the atoms.

For the reaction given in the exercise, \[ \text{HCO}_3^- + \text{H}_2\text{PO}_4^- \rightarrow \text{H}_3\text{PO}_4 + \text{CO}_2 + \text{H}_2\text{O}\] the equation is balanced because the number of each type of atom (hydrogen, oxygen, carbon, and phosphorous) is equal on both sides. Practicing balancing such equations helps in grasping complex reactions and is essential for anyone studying chemistry.

Bicarbonate and Phosphate Reactions

These reactions are particularly interesting as they involve bicarbonate ( ext{HCO}_3^-), a common compound known for its role in baking and pharmaceuticals, and phosphate ions, which are critical in biological systems. When these two anions react in water, an acid-base reaction occurs.

• Bicarbonate, acting as the base, accepts a proton from the dihydrogen phosphate, releasing carbon dioxide gas.
• The dihydrogen phosphate ( ext{H}_2 ext{PO}_4^-) acts as the acid and donates a proton.

The balanced reaction equation: \[ \text{HCO}_3^- + \text{H}_2\text{PO}_4^- \rightarrow \text{H}_3\text{PO}_4 + \text{CO}_2 + \text{H}_2\text{O}\] describes the formation of carbon dioxide, phosphoric acid ( ext{H}_3 ext{PO}_4), and water. This reaction showcases not only the role of bicarbonate and phosphate ions in chemistry but also highlights how they can be utilized in everyday applications. It emphasizes the importance of understanding chemical reactions at a molecular level, as they have practical implications in various industries, including food and healthcare.