Problem 22 - Chemistry: Principles and Reactions

Question

Solution A has a pH of 12.32. Solution B has \(\left[\mathrm{H}^{+}\right]\) three times as large as that of solution \(A\). Solution \(C\) has a \(\mathrm{pH}\) half that of solution \(\mathrm{A}\). (a) What is \(\left[\mathrm{H}^{+}\right]\) for all three solutions? (b) What is the \(\mathrm{pH}\) of solutions \(\mathrm{B}\) and \(\mathrm{C}\) ? (c) Classify each solution as acidic, basic, or neutral.

Step-by-Step Solution

Answer

Question: Calculate the H+ concentration for all three solutions, the pH of solutions B and C, and classify each solution as acidic, basic, or neutral. Answer: Step 1: Calculate H+ concentration for solution A H+(A) = 10^(-12.32) Step 2: Calculate H+ concentration for solution B H+(B) = 3 × H+(A) Step 3: Calculate H+ concentration for solution C pH(C) = 0.5 × pH(A) H+(C) = 10^(-pH(C)) Step 4: Calculate pH for solutions B and C pH(B) = -log[H+(B)] pH(C) = -log[H+(C)] Step 5: Classify the solutions as acidic, basic, or neutral Based on the calculated pH values, classify solutions A, B, and C as acidic (pH < 7), neutral (pH = 7), or basic (pH > 7).

Step 1: Calculate H+ concentration for solution A

Using the provided pH value for solution A, we can calculate the H+ concentration: pH = -log[H+] 12.32 = -log[H+(A)] To find H+(A), we take the inverse log of both sides or 10^(-pH): H+(A) = 10^(-12.32)

Step 2: Calculate H+ concentration for solution B

We are given that the H+ concentration of solution B is three times as large as that of solution A: H+(B) = 3 × H+(A)

Step 3: Calculate H+ concentration for solution C

We are given that the pH of solution C is half that of solution A: pH(C) = 0.5 × pH(A) Using the relationship between pH and H+: pH(C) = -log[H+(C)] Calculating the H+ concentration for solution C using the inverse log formula: H+(C) = 10^(-pH(C))

Step 4: Calculate pH for solutions B and C

Now that we have the H+ concentrations for solutions B and C, we can find their pH values using the same relationship: pH = -log[H+]

Step 5: Classify the solutions as acidic, basic, or neutral

We can classify the solutions based on their pH values: - If pH < 7, the solution is acidic. - If pH = 7, the solution is neutral. - If pH > 7, the solution is basic. Using the pH values calculated in the previous steps, we can classify solutions A, B, and C.

Key Concepts

Acidic Solutions

In chemistry, acidic solutions are those with a pH less than 7. The pH scale is a measure of how acidic or basic a solution is, with lower pH numbers indicating higher acidity. This is because pH is inversely related to the concentration of hydrogen ions ( [H^+] ).

• A solution with a higher concentration of [H^+] is considered more acidic.
• Acidity increases as the pH value decreases. For example, if the pH of a solution is 3, it is more acidic than one with a pH of 5.

Understanding whether a solution is acidic is crucial in various chemical applications, such as calculating reaction rates or understanding biological processes.
Next time you come across solutions in your experiments, remember that the pH can tell you much about the nature of the solution.

Basic Solutions

Basic solutions, in contrast to acidic ones, have a pH greater than 7. These solutions have lower concentrations of hydrogen ions ( [H^+] ) compared to neutral or acidic solutions.

• As the pH increases above 7, the solution becomes more basic. For example, a solution with a pH of 10 is more basic than one with a pH of 8.
• The lower the concentration of [H^+] , the more basic the solution will be.

Basic solutions, also known as alkaline solutions, can be found in everyday substances like household cleaning agents and baking soda. They play a significant role in various industrial and cleaning processes.
It's essential to handle basic solutions with care, as they may cause skin irritation or chemical burns when in high concentrations.

H+ Concentration

The concentration of hydrogen ions, denoted as [H^+], plays a central role in determining the acidity or basicity of a solution. The formula that connects pH and [H^+] is: \[ ext{pH} = -\log [H^+] \]

• When calculating the [H^+], one can use the inverse log (or antilog) to convert a pH value back to [H^+] concentration: [H^+] = 10^{-\text{pH}}
• Knowing either the pH or [H^+] helps in determining if a solution is acidic, basic, or neutral.

For example, for Solution A, with a pH of 12.32, we use [H^+] = 10^{-12.32}to calculate its hydrogen ion concentration. Understanding [H^+] is essential for many fields, especially in acid-base chemistry and environmental science.

pH Classification

Chemists use the pH scale to classify solutions as acidic, basic, or neutral. This classification helps in understanding the chemical properties and potential reactivity of a solution.

• If pH < 7, the solution is acidic.
• If pH = 7, the solution is neutral, akin to pure water.
• If pH > 7, the solution is basic.

By calculating the pH values of solutions B and C from the original exercise, we understood the nature of different solutions.
For instance, a solution like Solution A with a high pH of 12.32 is classified as basic. Understanding these categories are foundational in lab experiments, and testing the pH is a common practice to determine a solution's characteristics or to monitor reactions in progress.