Question

What is the \(\mathrm{pH}\) of the following solutions? Identify each as acidic, basic, or neutral. (a) \(0.0010 \mathrm{M} \mathrm{KOH}\) (b) \(0.0050 \mathrm{M} \mathrm{NaOH}\) (c) \(0.0010 M \mathrm{HCl}\)

Short answer

(a) The pH of 0.0010 M KOH is 11 and it is a basic solution. (b) The pH of 0.0050 M NaOH is 11.7 and it is a basic solution. (c) The pH of 0.0010 M HCl is 3 and it is an acidic solution.

Step-by-step solution

Calculate the pOH of KOH and NaOH solutions

Using the formula pOH = -log[OH-], calculate the pOH for both the KOH and NaOH solutions. For KOH, the concentration of OH- is 0.0010 M, therefore pOH = -log(0.0010) = 3. For NaOH, OH- concentration is 0.0050 M, so pOH = -log(0.0050) = 2.3

Calculate the pH of KOH and NaOH solutions

Now, calculate the pH of the KOH and NaOH solutions using the formula pH = 14 - pOH. For KOH, pH = 14 - 3 = 11, which identifies this as a basic solution. For NaOH, pH = 14 - 2.3 = 11.7, also identifying it as a basic solution.

Calculate the pH of the HCl solution

For the HCl solution, calculate the pH using the formula pH = -log[H+]. The concentration of H+ for HCl is 0.0010 M, therefore pH = -log(0.0010) = 3. This identifies HCl as an acidic solution.

Key concepts

Understanding Acidic Solutions

An acidic solution is characterized by a pH value of less than 7. The lower the pH, the more acidic the solution is. In an acidic solution, there is a higher concentration of hydrogen ions ([H^+]) compared to hydroxide ions ([OH^-]).
This imbalance is what makes a solution acidic. One common example of an acidic solution is hydrochloric acid (HCl).
In the exercise, the HCl solution has a concentration of 0.0010 M. Using the pH formula, \(\mathrm{pH} = -\log [H^+]\), we find the pH to be 3.
This low pH value confirms it as an acidic solution. Remember, solutions with a pH nearing zero are extremely acidic!
Acidic solutions can be naturally occurring like lemon juice or man-made like sulfuric acid used in industry.

• They taste sour and can conduct electricity.
• They're capable of turning blue litmus paper red.

Exploring Basic Solutions

Basic solutions, also known as alkaline solutions, have a pH greater than 7. The higher the pH, the more basic the solution is. These solutions have more hydroxide ions ([OH^-]) than hydrogen ions ([H^+]).
Examples include solutions of potassium hydroxide (KOH) and sodium hydroxide (NaOH), both of which were used in the exercise.

For KOH, with a concentration of 0.0010 M, using the formula for pOH (\(\mathrm{pOH} = -\log[OH^-]\)), we calculate the pOH to be 3. Using the relation \(\mathrm{pH} = 14 - \mathrm{pOH}\), the pH is 11.

NaOH, with a concentration of 0.0050 M, yields a pOH of 2.3 and a pH of 11.7.These pH values confirm that both solutions are basic.
Basic solutions:

• Feel slippery to the touch.
• Turn red litmus paper blue.
• Are commonly seen in household cleaners like ammonia and baking soda solutions.

The Nature of Neutral Solutions

Neutral solutions have a perfect balance between hydrogen ions and hydroxide ions, with a pH value exactly at 7. Pure water is the most iconic example of a neutral solution. This is because each molecule of water dissociates into one hydrogen ion and one hydroxide ion, balancing each other out perfectly.
In real-world circumstances, neutral pH does not vary as easily with dilution, because the concentration of both ions is intrinsically minimal and remains balanced.

• Neutral solutions are generally neither acidic nor basic.
• They do not affect the color of litmus paper.

Understanding this balance is crucial as it forms the basis for many biological and chemical processes. While the provided exercise did not specifically include a neutral solution, recognizing its characteristics can help comfortably compare and identify solutions that straddle the line between being acidic or basic.