A pKa to KA calculator is a useful tool in chemistry that helps convert between two important measures of acid strength: pKa and Ka.
pKa, or the negative logarithm of the acid dissociation constant, is a measure of how easily an acid gives up a proton. On the other hand, Ka, or the acid dissociation constant, directly represents the extent to which an acid dissociates in an aqueous solution.
Convert pKa to KA Calculator
| pKa | Ka |
|---|---|
| 4.76 | 1.74 × 10^(-5) |
| 3.00 | 1.00 × 10^(-3) |
| 7.50 | 3.16 × 10^(-8) |
| 9.25 | 5.62 × 10^(-10) |
| 2.15 | 7.08 × 10^(-3) |
To calculate these values, we used the formula:
Ka = 10^(-pKa)
For example, for the first row: Ka = 10^(-4.76) = 1.74 × 10^(-5)
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pKa to KA Conversion Formula
The relationship between pKa and Ka is defined by a simple logarithmic equation:
pKa = -log₁₀(Ka)
Conversely, to calculate Ka from pKa, we use the inverse logarithmic function:
Ka = 10^(-pKa)
These formulas form the basis of any pKa to KA calculator, allowing for quick and accurate conversions between the two values.
How do you convert pKa to KA?
Converting pKa to Ka involves a few simple steps:
- Start with the pKa value you want to convert.
- Recognize the relationship: pKa = -log₁₀(Ka)
- Rearrange the equation to solve for Ka: Ka = 10^(-pKa)
- Use a calculator to compute 10 raised to the power of the negative pKa value.
For example, if you have a pKa of 4.5: Ka = 10^(-4.5) = 3.16 × 10^(-5)
This process can be easily automated using a KA to pKa calculator, which performs these calculations instantly.
What is the pKa of 4.76 to Ka?
Let’s apply the conversion process to a specific example:
Given pKa = 4.76, we need to find Ka.
Using the formula Ka = 10^(-pKa):
Ka = 10^(-4.76) Ka = 1.74 × 10^(-5)
Therefore, a pKa of 4.76 corresponds to a Ka of 1.74 × 10^(-5).
This value indicates that the acid is relatively weak, as it has a small Ka value (much less than 1), meaning it doesn’t dissociate extensively in solution.
How is pKa different to Ka?
pKa and Ka both describe acid strength, they differ in several key aspects:
- Scale: Ka is a direct measure of the acid dissociation constant, while pKa is a logarithmic scale.
- Range: Ka values can span many orders of magnitude (e.g., 10^(-15) to 10^(15)), while pKa values typically range from about -2 to 16 for common acids.
- Interpretation: A higher Ka indicates a stronger acid, whereas a lower pKa indicates a stronger acid.
- Ease of use: pKa values are often easier to work with due to their more manageable range.
- Logarithmic nature: pKa represents the negative logarithm of Ka, similar to how pH represents the negative logarithm of hydrogen ion concentration.
Is Ka directly proportional to pKa?
No, Ka is not directly proportional to pKa. Instead, they have an inverse logarithmic relationship.
As pKa increases:
- Ka decreases exponentially
- The acid becomes weaker
As pKa decreases:
- Ka increases exponentially
- The acid becomes stronger
How to Calculate Ka and pKa from pH and Concentration
Let’s focus on weak acids for this explanation.
- pH = 4.5
- Initial concentration (C₀) = 0.1 M
- Calculate [H⁺]: [H⁺] = 10^(-4.5) = 3.16 × 10^(-5) M
- Calculate [A⁻]: [A⁻] = [H⁺] = 3.16 × 10^(-5) M
- Calculate [HA]: [HA] = 0.1 – (3.16 × 10^(-5)) ≈ 0.1 M
- Calculate Ka: Ka = (3.16 × 10^(-5))² / 0.1 = 1.00 × 10^(-8)
- Calculate pKa: pKa = -log₁₀(1.00 × 10^(-8)) = 8.00
Therefore, for this weak acid solution:
- Ka = 1.00 × 10^(-8)
- pKa = 8.00
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