Question

An antacid purchased at a local drug store has a pOH of \(2.3 .\) Calculate the \(\mathrm{pH},\left[\mathrm{H}^{+}\right],\) and \(\left[\mathrm{OH}^{-}\right]\) of this solution. Is the antacid acidic or basic?

Short answer

The antacid has a pH of 11.7, making it basic. The concentration of H⁺ ions is approximately \(2.0 \times 10^{-12} \, M\), and the concentration of OH⁻ ions is approximately \(5.0 \times 10^{-3} \, M\).

Step-by-step solution

Calculate pH

To calculate the pH of the solution, we can use the formula: pH = 14 - pOH Given pOH = 2.3, we plug it into the formula: pH = 14 - 2.3 = 11.7

Calculate the concentration of H⁺ ions

To calculate the concentration of H⁺ ions, we use the equation: \([H^+]=10^{-\mathrm{pH}}\) Now, plug in the pH value calculated in step 1: \([H^+] = 10^{-11.7}\) \([H^+] \approx 2.0 \times 10^{-12} \, M\)

Calculate the concentration of OH⁻ ions

To calculate the concentration of OH⁻ ions, we will use the equation: \([OH^-] = 10^{-\text{pOH}}\) Now, plug in the given pOH value: \([OH^-] = 10^{-2.3}\) \([OH^-] \approx 5.0 \times 10^{-3} \, M\)

Determine if the antacid is acidic or basic

Now that we know that the pH of the antacid solution is 11.7, we can use the pH scale to determine if the solution is acidic, neutral, or basic: - A solution with pH less than 7 is acidic - A solution with pH equal to 7 is neutral - A solution with pH greater than 7 is basic Since the pH of the antacid solution is greater than 7, the antacid is considered to be basic.

Key concepts

pOH

Understanding pOH is essential in chemistry, especially when dealing with basic solutions. pOH is a measure of hydroxide ion concentration in a solution. It's complementary to pH, which measures hydrogen ion concentration. Together, they help describe the acidity or basicity of a solution. The scale goes from 0 to 14, similar to pH.To find pOH, you can use the formula:\[ \text{pOH} = 14 - \text{pH} \]This relationship shows that if you know either the pH or pOH, you can easily calculate the other. It highlights the inverse relationship between the concentration of hydrogen ions and hydroxide ions in a solution.

• Low pOH means high hydroxide ion concentration and indicates a basic solution.
• High pOH signals a low hydroxide ion concentration, pointing to an acidic solution.

This balance equips chemists to handle various chemical reactions requiring precise measurements of acidity or basicity.

Concentration of H+ ions

The concentration of hydrogen ions (\([H^+]\)) in a solution quantifies its acidity. It can be derived from the pH of the solution using the formula:\[ [H^+] = 10^{-\text{pH}} \]This expression, rooted in the exponentiation of the negative pH value, tells us how concentrated the hydrogen ions are.For example, in the given problem, we calculated the pH as 11.7 using the reverse of the pOH formula. By inserting this value into the above equation:\[ [H^+] = 10^{-11.7} \approx 2.0 \times 10^{-12} \text{ M} \]This low concentration indicates that the solution is not acidic, which is confirmed by the high pH.Knowing the \([H^+]\) allows scientists to understand reaction rates. Many reactions depend on [H^+] because it's a critical reactant in acid-base reactions. Hence, calculating this ion concentration is essential in analytical chemistry.

Acidic or Basic

The determination of whether a solution is acidic or basic heavily relies on its pH value. The pH scale, ranging from 0 to 14, provides a simple way to measure the acidity or basicity of a solution:

• A pH less than 7 indicates an acidic solution.
• A pH equal to 7 suggests the solution is neutral.
• A pH greater than 7 means the solution is basic.

In the context of the given problem, the pH was found to be 11.7. This value clearly falls in the basic category. Knowing a solution's pH not only tells us its acidity or basicity but also informs us about the potential chemical behaviors in the solution. The ability to determine whether a solution is acidic or basic is crucial in fields like pharmacology where, for instance, antacids need to be basic to neutralize stomach acids effectively. This understanding ensures that they can effectively perform their intended function of raising the pH of an acidic environment, like an upset stomach, to alleviate discomfort.