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calculate the phone of a buffer prepared by mixing 300cc of 0.3M Nh3 and 500cc of 0.5M NH4CL KB for NH3=1.8 10^-5​

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student-name Aniket Padhi asked in Chemistry

A buffer solution is prepared in which the concentration of NH3 is 0.30 M and the concentration of NH4+ is 0.20 M. If the equilibrium constant , Kb for NH3 equals 1.8 x 10-5, what is the pH of this solution?

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student-name Arti answered this

9826 helpful votes in Chemistry, Class I

First calculate pKb by using this equation

pKb = -logKb

= - log [1.8 × 10-5]

= 4.774

Then calculate the pOH using Henderson–Hasselbalch equation

pOH = pKb + log (salt/base)

pOH = 4.774 + log (0.20/ 0.30)

= 4.774 + log 0.20 - log 0.30

= 4.774 -0.698-(-0.522)

= 4.598

Since, pOH + pH = 14

pH = 14 - pOH

pH = 14 - 4.598

pH = 9.402