Problem 76 - Chemistry Matter and Change

Question

Solution A has a pH of 2.0. Solution B has a pH of 5.0. Which solution is more acidic? Based on the H+ ion concentrations in the two solutions, how many times more acidic?

Step-by-Step Solution

Answer

Solution A is more acidic and is 1000 times more acidic than Solution B.

Step 1: Understanding pH

The pH scale measures the acidity or basicity of a solution, with a lower pH value indicating a more acidic solution. A pH of 7 is neutral, values less than 7 indicate acidity, and values greater than 7 indicate basicity.

Step 2: Comparing pH Levels of Solutions

Solution A has a pH of 2.0, and Solution B has a pH of 5.0. Since pH measures acidity, the solution with the lower pH is more acidic. Therefore, Solution A is more acidic than Solution B.

Step 3: Understanding the pH and H+ Ion Concentration Relationship

The pH of a solution is inversely related to the concentration of hydrogen ions (H+). Specifically, \[\text{pH} = -\log_{10} [\text{H}^+]\]. Thus, a lower pH corresponds to a higher concentration of H+ ions.

Step 4: Calculating H+ Ion Concentration for Solution A

For Solution A with a pH of 2.0, calculate the H+ ion concentration: \([\text{H}^+] = 10^{-2.0} = 0.01 \, \text{M}\).

Step 5: Calculating H+ Ion Concentration for Solution B

For Solution B with a pH of 5.0, calculate the H+ ion concentration: \([\text{H}^+] = 10^{-5.0} = 0.00001 \, \text{M}\).

Step 6: Determining How Many Times More Acidic Solution A Is Compared to Solution B

To find out how many times more acidic Solution A is compared to Solution B, divide the H+ ion concentration of Solution A by that of Solution B: \[\frac{[\text{H}^+]_{A}}{[\text{H}^+]_{B}} = \frac{0.01}{0.00001} = 1000\].

Step 7: Conclusion

Solution A is 1000 times more acidic than Solution B because its H+ ion concentration is 1000 times greater.

Key Concepts

Acidic Solutions

Acidic solutions are a fascinating area of chemistry that many students encounter during their studies. When we talk about solutions being "acidic," we mean that they have a higher concentration of hydrogen ions (H extsuperscript{+}). An acidic solution is one where the pH is less than 7. Anything less than 7 on the pH scale is considered acidic, with lower numbers indicating stronger acid presence. These types of solutions often occur naturally and can be found in many everyday items, like citrus fruits (think lemon or lime juice) or vinegar. The acidity is important because it affects how these substances interact in the environment and within our bodies. Understanding acidic solutions also helps in various fields like medicine, environmental science, and food science. Those fields often look at acidity to assess effects on ecosystems, human health, and food quality.

Hydrogen Ion Concentration

The hydrogen ion concentration is central to the understanding of acidity. Simply put, the more hydrogen ions present in a solution, the more acidic the solution is. This concentration is often represented with the symbol (H extsuperscript{+}).The connection between hydrogen ion concentration and pH is governed by a log scale. The formula for pH is \(\text{pH} = -\log_{10} [\text{H}^+]\). This means that even a small change in pH signifies a large change in hydrogen ion concentration.For example, if you calculate the H extsuperscript{+} concentration for a solution with a pH of 2, you find it is \(10^{-2.0} = 0.01\, \text{M}\). On the other hand, a solution with a pH of 5 has an H extsuperscript{+} concentration of \(10^{-5.0} = 0.00001\, \text{M}\). Thus, the lower the pH, the greater the concentration of hydrogen ions.

pH Scale

The pH scale is a simple tool that helps us understand the acidity or basicity of solutions. It ranges from 0 to 14, with a pH of 7 being neutral like pure water.

• Values less than 7 are acidic, indicating a higher concentration of hydrogen ions.
• Values greater than 7 are basic (or alkaline), indicating a lower concentration of hydrogen ions.
• The scale is logarithmic, meaning each whole number change on the scale corresponds to a tenfold change in H\(^+\) concentration.

For instance, a solution with a pH of 4 is ten times more acidic than a solution with a pH of 5. Understanding the pH scale is crucial as it applies to fields such as agriculture, pharmaceuticals, and environmental science where maintaining or altering pH levels can be significant for specific applications.