What is the pH ofa 6.50 x 10-3 M KOH solution?(Hint: this is a basic solution– concentration is of OH-)
The correct answer and explanation is :
To determine the pH of a 6.50 × 10⁻³ M KOH solution, follow these steps:
Step 1: Identify Key Information
- KOH is a strong base, meaning it dissociates completely in water:
[
\text{KOH} \rightarrow \text{K}^+ + \text{OH}^-
] - The concentration of hydroxide ions (\text{OH}^-) is equal to the given concentration of KOH:
[
[\text{OH}^-] = 6.50 \times 10^{-3} M
]
Step 2: Calculate pOH
The pOH is calculated using the formula:
[
\text{pOH} = -\log [\text{OH}^-]
]
[
\text{pOH} = -\log (6.50 \times 10^{-3})
]
Using a calculator:
[
\text{pOH} \approx 2.19
]
Step 3: Determine pH
Since the relationship between pH and pOH is:
[
\text{pH} + \text{pOH} = 14
]
[
\text{pH} = 14 – 2.19
]
[
\text{pH} \approx 11.81
]
Final Answer:
The pH of the 6.50 × 10⁻³ M KOH solution is 11.81, confirming it is a basic solution.
Explanation (300 Words)
The pH scale ranges from 0 to 14, where values below 7 are acidic, above 7 are basic, and exactly 7 is neutral. Since potassium hydroxide (KOH) is a strong base, it dissociates completely in water to release hydroxide ions (OH⁻), making the solution basic.
To find the pH, we first determine the pOH using the formula pOH = -log[OH⁻]. Plugging in the concentration 6.50 × 10⁻³ M, we obtain pOH ≈ 2.19. Since pH and pOH are related by the equation pH + pOH = 14, solving for pH gives pH ≈ 11.81.
A pH of 11.81 confirms the solution is basic because it is significantly higher than 7. This makes sense because KOH is a strong base and contributes a relatively high concentration of hydroxide ions to the solution.
In practical applications, knowing the pH of a solution is important in chemistry, medicine, and environmental science. For example, alkaline solutions like KOH are used in soap-making, cleaning agents, and industrial processes where strong bases are needed.
This problem reinforces the importance of understanding logarithmic functions in pH calculations and highlights how strong bases completely dissociate in aqueous solutions.
