Hydroxide Ions and Basic Solutions

Oct 13, 2025 by wbrum.org 57 views

Understanding pH and Hydroxide Ions

In chemistry, pH is a measure of the concentration of hydrogen ions (H+) in a solution. It is a scale that ranges from 0 to 14, with 7 being neutral. A pH less than 7 is considered acidic, while a pH greater than 7 is considered basic. However, pH only tells us about the concentration of hydrogen ions, not about the concentration of hydroxide ions (OH-).

Hydroxide Ions and Basic Solutions

Hydroxide ions are the conjugate base of water (H2O). They are formed when a base reacts with water to produce hydroxide ions and hydrogen ions. The concentration of hydroxide ions in a solution is related to the pH of the solution. A higher pH indicates a higher concentration of hydroxide ions.

The Relationship Between pH and Hydroxide Ions

The relationship between pH and hydroxide ions can be expressed using the following equation:

pH + pOH = 14

where pOH is the negative logarithm of the concentration of hydroxide ions.

Calculating pOH

To calculate pOH, we can use the following equation:

pOH = 14 - pH

Calculating Hydroxide Ion Concentration

To calculate the concentration of hydroxide ions, we can use the following equation:

[OH-] = 10^(-pOH)

Analyzing the Options

Now that we have a better understanding of pH and hydroxide ions, let's analyze the options:

A. Baking Soda, pH = 9

Baking soda is a base with a pH of 9. Using the equation pOH = 14 - pH, we can calculate the pOH of baking soda:

pOH = 14 - 9 pOH = 5

Using the equation [OH-] = 10^(-pOH), we can calculate the concentration of hydroxide ions in baking soda:

[OH-] = 10^(-5) [OH-] = 0.00001 M

B. Milk, pH = 6

Milk is a slightly acidic solution with a pH of 6. Using the equation pOH = 14 - pH, we can calculate the pOH of milk:

pOH = 14 - 6 pOH = 8

Using the equation [OH-] = 10^(-pOH), we can calculate the concentration of hydroxide ions in milk:

[OH-] = 10^(-8) [OH-] = 0.00000001 M

C. Tomato Juice, pH = 3.5

Tomato juice is an acidic solution with a pH of 3.5. Using the equation pOH = 14 - pH, we can calculate the pOH of tomato juice:

pOH = 14 - 3.5 pOH = 10.5

Using the equation [OH-] = 10^(-pOH), we can calculate the concentration of hydroxide ions in tomato juice:

[OH-] = 10^(-10.5) [OH-] = 0.000000000001 M

D. Vinegar, pH = 2

Vinegar is an acidic solution with a pH of 2. Using the equation pOH = 14 - pH, we can calculate the pOH of vinegar:

pOH = 14 - 2 pOH = 12

Using the equation [OH-] = 10^(-pOH), we can calculate the concentration of hydroxide ions in vinegar:

[OH-] = 10^(-12) [OH-] = 0.0000000000001 M

Conclusion

Based on the calculations, we can see that baking soda has the greatest number of hydroxide ions, followed by milk, tomato juice, and vinegar. This is because baking soda has a higher pH than the other options, indicating a higher concentration of hydroxide ions.

Key Takeaways

pH is a measure of the concentration of hydrogen ions in a solution.
Hydroxide ions are the conjugate base of water.
The concentration of hydroxide ions is related to the pH of the solution.
A higher pH indicates a higher concentration of hydroxide ions.
Baking soda has the greatest number of hydroxide ions among the options.
Frequently Asked Questions: Hydroxide Ions and pH =====================================================

Q: What is pH and how is it related to hydroxide ions?

A: pH is a measure of the concentration of hydrogen ions (H+) in a solution. It is a scale that ranges from 0 to 14, with 7 being neutral. A pH less than 7 is considered acidic, while a pH greater than 7 is considered basic. The concentration of hydroxide ions (OH-) is related to the pH of the solution, with a higher pH indicating a higher concentration of hydroxide ions.

Q: How do I calculate the concentration of hydroxide ions in a solution?

A: To calculate the concentration of hydroxide ions, you can use the following equation:

[OH-] = 10^(-pOH)

where pOH is the negative logarithm of the concentration of hydroxide ions.

Q: What is the relationship between pH and pOH?

A: The relationship between pH and pOH can be expressed using the following equation:

pH + pOH = 14

Q: How do I calculate pOH?

A: To calculate pOH, you can use the following equation:

pOH = 14 - pH

Q: What is the difference between a strong base and a weak base?

A: A strong base is a base that completely dissociates in water to produce hydroxide ions, while a weak base is a base that only partially dissociates in water to produce hydroxide ions. Strong bases have a higher pH than weak bases.

Q: What is the pH of a solution that contains 0.1 M hydroxide ions?

A: To calculate the pH of a solution that contains 0.1 M hydroxide ions, you can use the following equation:

pOH = -log[OH-] pOH = -log(0.1) pOH = 1

Using the equation pH + pOH = 14, we can calculate the pH of the solution:

pH = 14 - pOH pH = 14 - 1 pH = 13

Q: What is the pH of a solution that contains 0.01 M hydroxide ions?

A: To calculate the pH of a solution that contains 0.01 M hydroxide ions, you can use the following equation:

pOH = -log[OH-] pOH = -log(0.01) pOH = 2

Using the equation pH + pOH = 14, we can calculate the pH of the solution:

pH = 14 - pOH pH = 14 - 2 pH = 12

Q: What is the pH of a solution that contains 0.001 M hydroxide ions?

A: To calculate the pH of a solution that contains 0.001 M hydroxide ions, you can use the following equation:

pOH = -log[OH-] pOH = -log(0.001) pOH = 3

Using the equation pH + pOH = 14, we can calculate the pH of the solution:

pH = 14 - pOH pH = 14 - 3 pH = 11

Q: What is the pH of a solution that contains 0.0001 M hydroxide ions?

A: To calculate the pH of a solution that contains 0.0001 M hydroxide ions, you can use the following equation:

pOH = -log[OH-] pOH = -log(0.0001) pOH = 4

Using the equation pH + pOH = 14, we can calculate the pH of the solution:

pH = 14 - pOH pH = 14 - 4 pH = 10

Conclusion

In this article, we have discussed the relationship between pH and hydroxide ions, and provided answers to frequently asked questions about hydroxide ions and pH. We have also calculated the pH of solutions that contain different concentrations of hydroxide ions.