Answer to Question #301924 in General Chemistry for Paul Hackman

Question

4. Write two equations to depict the amphitropic nature of water.

(b) define the following: (I) pH and (II) pKa

(c).For a reaction between a weak acids and water as shown, prove that pH =pKa -log [acid/base].

HB(acid) + H₂O = H₃O⁺ + B^-

(d) List the factors that affect the solubility of a substances.

(e) Calculate the solubility in grams per litre of silver sulphide if the K_sp of Ag₂S is 6.3 x 10^-50

Answer 1

A) The pH is a measure of the concentration of hydrogen ions in an aqueous solution. ... Essentially, pKa tells you what the pH needs to be in order for a chemical species to donate or accept a proton. The relationship between pH and pKa is described by the Henderson-Hasselbalch equation

B) The procedure for calculating the pH of a solution of a weak base is similar to that of the weak acid in the example. However, the variable x will represent the concentration of the hydroxide ion. The pH is found by taking the negative logarithm to get the pOH, followed by subtracting from 14 to get the pHpH = pK_a + log[A⁺]/[HA]

Modified... for weak bases

pOH = pK_b + log[HB]/[B^-]

pOH = pK_b + log[Acid]/[Base]

Let's test it out dude....

If the pH = 3.8, then the pOH = 14 - 3.8

pOH = 10.2

Also, since the percent ionization of HB was 67%, that means there is 67% B^- and 33% HB in solution.

Use these values in the equation to solve for pK_b

pOH = pK_b + log[HB]/[B^-]

10.2 = pK_b + log[0.33]/[0.67]

10.2 = pK_b - 0.31

pK_b = 10.2 + 0.31

pK_b = 10.51

*Fingers crossed Blake...

One last thing.

HB is the acid,

H₂O is the base

B^- is the conjugate base

H₃O⁺ is the conjugate acid