Question

In: Chemistry

What mass of ammonium chloride should be added to 2.60 L of a 0.145 M NH3...

What mass of ammonium chloride should be added to 2.60 L of a 0.145 M NH3 in order to obtain a buffer with a pH of 9.45?

Expert Solution

The pH of buffer is calculated using Hendersen Hassalbalch's equation. For basic buffer the equaiton is

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

Or

pH = pKa + log [base] / [salt]

Moles of base = Molarity X volume = 0.145 X 2.60 = 0.377 moles

pKa = 14 - pKb

Kb = 1.8 X 10⁻⁵ therefire pKb = -logKb = 4.745

pKa = 14- 4.745 = 9.255

pH = 9.45

pH = 9.45 = 9.255 + log [0.377 / [salt]

0.195 = log [0.377 / [salt]

Taking antilog

1.57 = 0.377 / [ salt]

[salt] = moles of salt = 0.2401

mass of salt (NH4Cl) = moles X molecular weight of NH4Cl

Molecular weight of NH4Cl = 53.5 g / mole

Mass of salt (NH4Cl0 = 0.2401 X 53.5= 12.85 grams

queen_honey_blossom answered 2 years ago

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