why is the buffer capacity of water smaller than the buffer capacity of the buff

Question

why is the buffer capacity of water smaller than the buffer capacity of the buffer?

Target pH of Buffer g of K2Hro,?1.tola-(Kl mo.I Measured pH of 40. mL of buffer . ol Measured pH of 40. mL of buffer after HCl is added 787 Buffer Capacity of buffer (in moles, scaled to 1L) Q.112 mols (show work below) Measured pH of 40. mL of water Co.57 Measured pH of 40. mL of water after HCl is added _2.(o4 Buffer Capacity of water (in moles, scaled to1L)? Discuss why and how the buffer capacity differs. Dicus why and how2.41x103 hanly fiom manual 2 mi of o.ao M HC (7,9?1-7672)(.040) (o.osa)C-040 00.20M 241x10 mo1s (a a3x.040 The buffer capacity of woter is much Smalkr than the butCer taspacity of the buffer

Explanation / Answer

We have, for a buffer solution,

pH = pKa + log ([conjugate base]/[acid])

For water, H2O and OH- are equal in concentration and always remanin in equilibrium. So, for water pH=pKa.

Therefore, addition of any acid or base to it will change its pH immediately. So, it has less buffer capacity.

On the other hand, for buffer, concentration of acid and its conjugate base are mixed in different concentration. Suppose, base is added to the solution. Base will react with the acid untill all the acids are exhausted. Till that period, it will resist the change in pH. Similar phenomenon occurs when base is added. This explains the reason of higher buffer capacity of buffer.

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