1. A buffer solution is prepared by mixing 50.0 mL of 0.300 M NH3 with 50.0 mL o

Question

1. A buffer solution is prepared by mixing 50.0 mL of 0.300 M NH3 with 50.0 mL of 0.300 M Nh4cl. the pKb of NH3 is 4.74

NH3 +H2O --> NH4+ + OH-

a. Calculate the [NH3} and [NH4Cl] in the buffer solution. calculate the pH of the buffer solution

b. 7.50 mL of 0.125 M HCl is added to the 100.0 mL of the buffer solution. Calculate the new [NH3} and [NH4Cl] for the buffer solution. Calculate the new pH of the solution.

c. 7.50 mL of 0.125 M NaOH is added to the 100.0 mL of the buffer solution. Calculate the new [NH3] and the [NH4Cl] for the buffer solution. Calculate the new pH of the solution

Explanation / Answer

a)

pOH=pKb+log[salt]/[base]

[NH3]=50*0.3=15

[NH4Cl]=50*0.3=15

pH=14-pOh=14-4.74=9.26

b)

[HCl]=7.5*0.125=0.9

[NH3]=14.1

[NH4Cl]=15.9

pH=14-4.74-log(15.9/14.1)=9.23

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