Question 9 of 10 Sapling Learning Map A Strong base is dissolved in 7 Assume tha

Question

Question 9 of 10 Sapling Learning Map A Strong base is dissolved in 7 Assume that the volume remains constant when the base is added. HA(aq)+ OH (aq Calculate the pKa value of the acid and determine the number of moles of acid initially present. Number Number pK, mol HA When the reaction x 10 what is the concentration ratio of conjugate base to acid? Number HA How many moles of strong base were initially added? Number mol OH A Previous 8 Give Up & view Solution Check Answer 0 Next a Exit Hint about us careers partners l privacy policy terms of use contact us help

Explanation / Answer

Pka value of acid:

Pka = -log[Ka]

Pka = -log(3.21*10-5)

Pka = 4.49

The number of mole of acid initially present = concentration * volume (in L)

= 0.2 M * 0.765 L

= 0.153 mol

The concentration ratio of conjugate base to acid when the reation is complete:

pH =Pka + log [A-]/[HA]

4.08 =4.49 +  log [A-]/[HA]

[A-]/[HA] = 0.389

Number of moles of base added initially

[HA] = 0.153 mol

[A-] / 0.153 = 0.389

[A-] = 0.153 * 0.389 = 0.0595 mol of OH-

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