Pka what is ka

Share Flipboard Email. Anne Marie Helmenstine, Ph. Chemistry Expert. Helmenstine holds a Ph. She has taught science courses at the high school, college, and graduate levels. Facebook Facebook Twitter Twitter. Updated February 04, Featured Video. Cite this Article Format. Helmenstine, Anne Marie, Ph. How to Calculate the pH of a Weak Acid. List of the Strong Acids and Key Facts.

Chemistry Terminology: Definition of pOH. Acid Dissociation Constant Definition: Ka. How to Make a Phosphate Buffer Solution. Here's How to Calculate pH Values. Your Privacy Rights. When dealing with equilibrium constant, remember adding water to an aqueous acid or base solution does not change its equilibrium constant. A pH value around 7 is neutral neither acidic nor basic , a pH value less than 7 is acidic, and a pH value greater than 7 is basic. Ka is the acid dissociation constant.

A large Ka value indicates a strong acid because it means an acid largely dissociates into its ions. A large Ka value also means the reaction arrow favors the formation of production. In contrast, a small Ka value means only a small amount of acid dissociates, indicating a weak acid. Besides being easier to work with, pKa values have an inverse relationship to acid strength.

In other words, a low pKa indicates a strong acid and vice versa. In some tables, you may find the pKa value listed, but you may need the Ka value to plug into your equations. You solve this by raising both sides of the original relationship to powers of 10 to get:. When pKa is a whole number, such as -7, this operation is easy to perform, but when it contains a fraction, such as 7.

Remember that pKa is expressed as a common logarithm base 10 and not as a natural logarithm base e , so you want to find a table or select a function on your calculator that raises the number to a power of 10 rather than a power of e.

Chris Deziel holds a Bachelor's degree in physics and a Master's degree in Humanities, He has taught science, math and English at the university level, both in his native Canada and in Japan. He began writing online in , offering information in scientific, cultural and practical topics. His writing covers science, math and home improvement and design, as well as religion and the oriental healing arts.

The specifics of how we can measure this are another story, but for our purposes, let me assure you that these types of equilibrium constants can be measured accurately. For H-I, it turns out that the equilibrium constant for this reaction is about 10,,, That means for every molecule of HI, there are 10 billion molecules of I -.

In other words, H-I donates its proton very readily to give its conjugate base, which is a prime example of a strong acid. So what? Note that these are somewhat oversimplified in that the solvent has been left out. Now comparing acidity between numbers with lots of exponents after them is not the most convenient way to do things. These are common — the Richter scale is logarithmic, for instance — an 8. To give you an idea of the scale, of pK a , this is the range of the smallest value for length the Planck length, 10 —35 meters , to the width of the known universe about 10 26 meters.

This website has a phenomenal animation of this.