×Suppose A 250 AALEKS: Philip Potapcha https://www-aw O ACOS, BASES AND AQUEOUS

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×Suppose A 250 AALEKS: Philip Potapcha https://www-aw O ACOS, BASES AND AQUEOUS EQUILIBRA MLFlas./GChegg Study Guided Sox C exe/1o u-igNslkr7j8P3/H-IBlzawus-f-68 h1Mx3p547r Calculating the composition of a buffer of a given pH A chemistry graduate student is given 450. ml of a 1.10 M acetic acid (HCH,CO2) solution. Acetic acid is a weak acid with K,-1.8 x 10 what mass of KCH,CO2 should the student dissolve in the HCH, CO2 solution to turn it into a buffer with pH-5.00 You may assume that the volume of the solution doesn't change when the KCH,CO is dissolved in it. Be sure your answer has a unit symbol, and round it to 2 significant digits

Explanation / Answer

we know that

acetic acid is a weak acid

and

CH3COOK is the salt of its cojugate base CH3COO-

so

they form a buffer solution

now

for buffers , according to hasselbach hendersen equation

pH = pKa + log[salt / acid]

also

pKa = -log Ka

so

pH = -log Ka + log [CH3COOK / CH3COOH]

given

pH = 5

Ka = 1.8 x 10-5

so

5 = -log 1.8 x 10-5 + log [CH3COOK / CH3COOH]

log [CH3COOK / CH3COOH] = 0.25527

[CH3COOK / CH3COOH] = 1.8

now

we know that

cocentration = moles / volume (L)

as the final volume is same for both of them

ratio of concentrations= ratio of moles

so

moles of CH3COOK / moles of CH3COOH = 1.8

moles of CH3COOK = 1.8 x moles of CH3COOH

now

we know that

moles = concentration x volume (L)

so

moles of CH3COOH taken = 1.1 x 0.45 = 0.495

so

moles of CH3COOOK = 1.8 x 0.495

moles of CH3COOK = 0.891

now

mass = moles x molar mass

molar mass of CH3COOK = 98 g/mol

so

mass of CH3COOK = 0.891 x 98

mass of CH3COOK = 87.32

so

87.32 grams of CH3COOH should be added

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