Pka and base strength relationship

Relationship between pka, ka, and acidity strength - CHEMISTRY COMMUNITY

pka and base strength relationship

I am trying to figure out if a drug that I have is acid or base and Remember pKa is the -log of the Ka and if you can remember the relationship. Ka and Kb are the acid and base dissociation constants which serve as quanitified measurements of the strength of an acid in solution, respectively. If the pKa describes an acidic equilibrium: HA = H+ + A- then its high value indicates a relatively weak acid. BH+ = B + H+ then its high value indicates a relatively strong base (wea pKa have an inverse relation with acidic strength.

pH, pKa, Ka, pKb, Kb - Organic Chemistry | Socratic

We apply the following principle to acid-base reactions: A stronger acid will tend to react with a stronger base to produce a weaker acid and a weaker base. The question is, how do we determine base strength? Draw out the conjugate bases of the acids on your pka table by removing a proton. The order of base strength is the inverse of acid strength. The weaker the acid, the stronger the conjugate base.

Acid Base Strength - Which Is Stronger?

Using this principle, you can also use the pKa table to give you the strengths of bases. I call this the inverse pKa table. Find the acid on the pKa table. Find the base on the inverse pKa table. Do the acid base reaction — that is, add a proton to the base and remove a proton from the acid.

Is the new acid stronger or weaker? Is the new base stronger or weaker? So CH4 is the acid and HO - is the base in this reaction. Doing the proposed acid base reaction, we transfer a proton from CH4 to HO. The products of this reaction would therefore be CH3 - and water.

pka and base strength relationship

Now we ask the question — how do these compare in strength to our starting acids and bases? Our product is a stronger acid. Our product is a stronger base. We need to go to a weaker acid-base pair see 2, above. The pKa measures how tightly a proton is held by a Bronsted acid.

A pKa may be a small, negative number, such as -3 or It may be a larger, positive number, such as 30 or The lower the pKa of a Bronsted acid, the more easily it gives up its proton. The higher the pKa of a Bronsted acid, the more tightly the proton is held, and the less easily the proton is given up.

  • pH, pKa, Ka, pKb, Kb

The pKa scale as an index of proton availability. Low pKa means a proton is not held tightly.

pka and base strength relationship

High pKa means a proton is held tightly. Some Bronsted acidic compounds; these compounds all supply protons relatively easily. For example, nitric acid and hydrochloric acid both give up their protons very easily.

Nitric acid in water has a pKa of On the other hand, acetic acid found in vinegar and formic acid the irritant in ant and bee stings will also give up protons, but hold them a little more tightly.

How to Use a pKa Table

Their pKas are reported as 4. Water can certainly give up a proton, but not very easily; it has a pKa of around Methane is not really an acid at all, and it has an estimated pKa of about Water is very, very weakly acidic; methane is not really acidic at all. The pKa measures the "strength" of a Bronsted acid.

pka and base strength relationship

A strong Bronsted acid is a compound that gives up its proton very easily. A weak Bronsted acid is one that gives up its proton with more difficulty. Going to a farther extreme, a compound from which it is very, very difficult to remove a proton is not considered to be an acid at all.

pka and base strength relationship

When a compound gives up a proton, it retains the electron pair that it formerly shared with the proton. It becomes a conjugate base. Looked at another way, a strong Bronsted acid gives up a proton easily, becoming a weak Bronsted base. The Bronsted base does not easily form a bond to the proton.

It is not good at donating its electron pair to a proton. It does so only weakly.

Relationship between Ka and Kb

In a similar way, if a compound gives up a proton and becomes a strong base, the base will readily take the proton back again. Effectively, the strong base competes so well for the proton that the compound remains protonated. The compound remains a Bronsted acid rather than ionizing and becoming the strong conjugate base. It is a weak Bronsted acid. The pKa scale and its effect on conjugate bases. This term is usually used to describe common acids such as sulfuric acid and hydrobromic acid.