Question

Predict the \(\mathrm{pH}(>7,<7,\) or \(\approx 7)\) of a \(\mathrm{NaHCO}_{3}\) solution.

Short answer

The pH of a NaHCO₃ solution is >7.

Step-by-step solution

Understand the Compound

Sodium bicarbonate (NaHCO₃) is a salt that results from the neutralization of a weak acid (carbonic acid, H₂CO₃) by a strong base (sodium hydroxide, NaOH). This implies the solution will be basic.

Hydrolysis Concept

The bicarbonate ion (HCO₃⁻) can react with water in a hydrolysis reaction, producing hydroxide ions (OH⁻), which increase the pH of the solution.

Write the Hydrolysis Equation

The hydrolysis reaction of the bicarbonate ion is:\[\text{HCO}_3^- + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3 + \text{OH}^-\]This shows the formation of hydroxide ions, making the solution basic.

Analyze the Ions

The presence of OH⁻ ions indicates the solution has more hydroxide ions than hydrogen ions, leading to a pH greater than 7.

Conclusion

Based on the hydrolysis reaction and the formation of OH⁻, we can predict that the NaHCO₃ solution will have a pH > 7.

Key concepts

Sodium Bicarbonate

Sodium bicarbonate, also known as baking soda, is a common compound with the chemical formula \( \mathrm{NaHCO}_3 \). It is often used in baking as a leavening agent and in various household cleaning products. This compound forms when sodium hydroxide (a strong base) neutralizes carbonic acid (a weak acid). As a result of this reaction, sodium bicarbonate acts as a salt. In aqueous solutions, it behaves in a characteristic manner that influences the pH due to the presence of bicarbonate ions.

Hydrolysis Reaction

The hydrolysis reaction is a chemical process in which a compound reacts with water, leading to the formation of new compounds. In the case of sodium bicarbonate, the bicarbonate ion \( \left( \text{HCO}_3^- \right) \) interacts with water during hydrolysis. This reaction is reversible and can be expressed as follows: - \( \text{HCO}_3^- + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3 + \text{OH}^- \)This equation highlights the production of hydroxide ions \( \left( \text{OH}^- \right) \), which plays a crucial role in the pH of the solution. The increase in hydroxide ions shows how hydrolysis of bicarbonate impacts the solution's properties.

Basic Solution

A solution is termed "basic" when it has an excess of hydroxide ions \( \left( \text{OH}^- \right) \) over hydrogen ions \( \left( \text{H}^+ \right) \). This is what happens when sodium bicarbonate is dissolved in water. The hydrolysis reaction of the bicarbonate ion generates more \( \text{OH}^- \) ions, thus increasing the basicity of the solution.

• Basic solutions have a pH greater than 7.
• They feel slippery to touch.
• They can turn red litmus paper to blue.

In the case of sodium bicarbonate, the solution is expected to have a pH greater than 7 due to the presence of these hydroxide ions.

Neutralization

Neutralization is the reaction between an acid and a base that results in the formation of water and a salt. For sodium bicarbonate, this process initially occurs when a strong base like sodium hydroxide reacts with a weak acid such as carbonic acid. This forms sodium bicarbonate, which is effectively the salt from the neutralization process. However, it is important to note that the solution of sodium bicarbonate isn’t neutral. Rather, it tends to be basic due to the effects of hydrolysis, where the bicarbonate ion participates in further reactions with water, releasing hydroxide ions that elevate the pH.

Bicarbonate Ion

The bicarbonate ion \( \left( \text{HCO}_3^- \right) \) is an intermediate form in the deprotonation of carbonic acid. It is a crucial component in the buffering systems of the blood, serving an essential role in maintaining pH balance. In aqueous solutions, this ion has the ability to participate in hydrolysis, as shown in the earlier reaction:- \( \text{HCO}_3^- + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3 + \text{OH}^- \)The generation of hydroxide ions from bicarbonate ions is significant because it dictates the basic nature of a sodium bicarbonate solution. As more hydroxide ions are produced, the capacity of the solution to resist changes in pH makes it an effective component in systems requiring pH stabilization.