Ph Of Weak Acid And Weak Base Formula

Acetic acid is a weak acid which ionizes only partially in water a few percent. Ph of a weak acid finding the ph of a weak acid is a bit more complicated than finding ph of a strong acid because the acid does not fully dissociate into its ions.

Monoprotic Acid Base Equilibria Ppt Download

Calculate the ph or poh quickly.

Ph of weak acid and weak base formula. The formula for the ph of a salt of a weak acid and base is ph 7 1 2 pka pkb where pka is the dissociation constant for a weak acid and pkb is the dissociation constant for a weak base. These can be used to calculate the ph of any solution of a weak acid or base whose ionization constant is known. Instead of an acid constant ka a base constant kb must be used.

Both nh 4 ions and ch 3 coo ions react respectively with oh and h ions furnished by water to form nh 4 oh weak base and ch 3 cooh acetic acid. The ionization constant can be used to calculate the amount ionized and from this the ph. If a weak base b accepts protons from water according to the equation 14 5 1 b h 2 o bh oh.

The higher ph of the 2 00 m nitrous acid is consistent with it being a weak acid and therefore not as acidic as a strong acid would be. Calculate ph and poh of a weak acid or base solution using simple formula quadratic equation and including autoionization of water. The ph of a 2 00 m solution of a strong acid would be equal to log 2 00 0 30.

Calculating ph of weak acid and base solutions the k text a and k text b values have been determined for a great many acids and bases as shown in tables 21 12 2 and 21 13 1. The ph equation is still the same ph log h but you need to use the acid dissociation constant ka to find h. Predict whether an aqueous solution of a salt will be acidic or alkaline and explain why by writing an appropriate equation.

The ph of a solution of a weak base can be calculated in a way which is very similar to that used for a weak acid. Ph of solution. Calculate the ph of a solution of a weak monoprotic weak acid or base employing the five percent rule to determine if the approximation 2 4 is justified.

Let ba represents such a salt. C 2 c 2 2 4 k a c 1 2 where c 1 is the concentration in mole litre of the weak acid ionisation constant k a and c 2 is that of the strong acid. Weak acids and bases are only partially ionized in their solutions whereas strong acids and bases are completely ionized when dissolved in water.

The acidity constant for acetic acid at 25 c is 1 75 10 5. The procedure for calculating the ph of a solution of a weak base is similar to that of the weak acid in the sample problem. I understand that the strong acid will dissociate completely and the weak acid will dissociate with an ionisation constant.

Weak Acids