llCalculator Periodic Table Question 2 of 10 Sapling Learning Strong base is dis

Question

llCalculator Periodic Table Question 2 of 10 Sapling Learning Strong base is dissolved in 535 ml of 0.400 M weak acid (K, 4.10 x10) to make a buffer with a pH of 3.93. Assume that the volume remains constant when the base is added. HAlay)+OH (a>H,o+A a) Calculate the pK, value of the acid and determine the number of moles of acid initially present mol HA When the reaction is complete, what is the concentration ratio of conjugate base to acid? How many moles of strong base were initially added? mol OH Give Up & VIew Soluton Check Answer NextExi / Hint

Explanation / Answer

pKa = - log(Ka)

= - log (4.10*10^-5)

= 4.387

Mol HA = molarity x volume

= 0.400 mol/L x 0.535 L

= 0.214 mol

From the Henderson-Hasselbalch equation

pH = pka + log (base/acid)

3.93 = 4.387 + log ( [A-]/[HA])

log ( [A-]/[HA]) = 3.93 - 4.387 = - 0.457

([A-]/[HA]) = 0.349

moles of the salt = moles of the NaOH added:

([A-]/[HA]) = 0.349

x / (0.214 - x) = 0.349
x = 0.074686 - 0.349x

x = 0.05536 = mol OH-

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