Phosphoric acid is a triprotic acid ( K a1 = 6.9 × 10 − 3 Ka1=6.9×10−3, K a2 = 6.2 × 10 − 8 Ka2=6.2×10−8, and K a3 = 4.8 × 10 − 13 Ka3=4.8×10−13). To find the pH of a buffer composed of H 2 PO − 4 ( aq ) H2PO4−(aq) and HPO 2 − 4 ( aq ) HPO42−(aq) , which p K a Ka value should be used in the Henderson–Hasselbalch equation?

To calculate the pH of the buffer composed of , we use the

Explanation:

Phosphoric acid is a triprotic acid and it will undergo three dissociation reaction each having their respective dissociation constants.

The chemical equation for the first dissociation reaction follows:

The chemical equation for the second dissociation reaction follows:

The chemical equation for the third dissociation reaction follows:

To form a buffer composed of , we use the of second dissociation process

To calculate the , we use the equation:

To calculate the pH of buffer, we use the equation given by Henderson Hasselbalch:

We are given:

= negative logarithm of second acid dissociation constant of phosphoric acid = 7.21

= concentration of conjugate base

= concentration of weak acid

Hence, to calculate the pH of the buffer composed of , we use the

hydrocarbons are organic compounds that contain only hydrogens and carbons. they can be saturated (those which contain only carbon-carbon single bonds) or unsaturated (those which contain carbon-carbon double or triple bonds) in nature. hydrocarbons can undergo several reactions like substitution, elimination etc.  

on substituting one or more hydrogen atoms in hydrocarbon it results in the formation of haloalkane. as the halogen atoms are large compared to the carbon and hydrogen atoms, due to which the molecular weight increases and the bond become polar because of presence electronegative halogen atom and results in the increase in boiling point of the haloalkane.

thus, the correct option is (b) that is the boiling point of the new compound increases on substituting a hydrogen atom with a halogen in a hydrocarbon.