How to calculate pKa from Ka?
Understand the Problem
The question is asking for the method to calculate the pKa value from the Ka value, which involves using the relationship between these two measures of acidity.
Answer
$ ext{pKa} = - ext{log}_{10}( ext{Ka})$
Answer for screen readers
The pKa value is calculated using the formula: $$ ext{pKa} = - ext{log}_{10}( ext{Ka}) $$. For a given Ka, apply this formula to find pKa.
Steps to Solve
- Understand the relationship between pKa and Ka
pKa is the negative logarithm (base 10) of the acid dissociation constant Ka. The relationship is given by the formula:
$$ ext{pKa} = - ext{log}_{10}( ext{Ka}) $$
- Calculate the logarithm of Ka
Find the base 10 logarithm of the given Ka value.
For example, if Ka is given as 1.8 x 10^{-5}, then
$$ ext{log}_{10}(1.8 imes 10^{-5}) $$
- Apply the negative sign
Apply the negative sign to the result from step 2 to get pKa.
$$ ext{pKa} = - ( ext{log}_{10} ( ext{Ka})) $$
So, if
$$ ext{log}_{10}(1.8 imes 10^{-5}) = -4.745$$, then
$$ ext{pKa} = -(-4.745) = 4.745$$
The pKa value is calculated using the formula: $$ ext{pKa} = - ext{log}_{10}( ext{Ka}) $$. For a given Ka, apply this formula to find pKa.
More Information
This relationship is used frequently in chemistry to relate the strength of an acid (Ka) to its pKa value. The smaller the pKa value, the stronger the acid.
Tips
A common mistake is forgetting to apply the negative sign or using a logarithm with an incorrect base (such as natural logarithm instead of base 10).
AI-generated content may contain errors. Please verify critical information
