"Phenylacetic acid, C7H7COOH, builds up in the blood of people with phenylketonuria. The pKa of phenylacetic acid is 4.32 at 25 ºC. What is the pH of a 0.15 M aqueous solution of calcium phenylacetate, Ca(C7H7COO)2, at 25 ºC?"

pH = 8.9

Explanation:

To solve this problem, we need to write the overall reaction of the aqueous solution of Ca(C₇H₇COO)₂:

Ca(C₇H₇COO)₂ <> Ca²⁺ + 2C₇H₇COO⁻

This means that the concentration of the phenyl acetate is 2 times the concentration of the calcium phenylacetate:

[C₇H₇COO⁻] = 2 * 0.15 = 0.30 M

We have the concentration of the phenylacetate, this is a conjugate base of the phenylacetic acid, therefore, we need the Kb of the conjugate. This can be calculated using the following expression:

Kw = Kb * Ka > Kb = Kw/Ka

And Ka = 10^(-pKa)

Replacing the values (Assuming Kw = 1x10⁻¹⁴)

Ka = 10⁽⁻⁴°³²⁾ = 4.786x10⁻⁵

Kb = 1x10⁻¹⁴ / 4.786x10⁻⁵ = 2.089x10⁻¹⁰

Now that we have Kb, we can write the reaction of the phenylacetate in water, and an ICE chart

        C₇H₇COO⁻ + H₂O <> C₇H₇COOH + OH⁻    Kb = 2.089x10⁻¹⁰

i)           0.30                                        0                0

e)          0.30-x                                     x                 x

Kb = [C₇H₇COOH] [OH⁻] / [C₇H₇COO⁻]      Replacing the above values

2.089x10⁻¹⁰ = x² / 0.30 - x    

As Kb is very small, x would be a very small value too, so we can neglect 0.30 - x to 0.30 only:

2.089x10⁻¹⁰ = x² / 0.30

2.089x10⁻¹⁰ * 0.30 = x²

√6.27x10⁻¹¹ = x

x = 7.92x10⁻⁶ M

This is the concentration of the phenylacetate and OH⁻. With this value we can calculate the pOH and then, the pH:

pOH = -log[OH⁻]

pOH = -log(7.92x10⁻⁶)

pOH = 5.1

Finally the pH:

pH = 14 - pOH

pH = 14 - 5.1

mechanics (greek   is that area of science concerned with the behaviour of physical bodies when subjected to forces or displacements, and the subsequent effects of the bodies on their environment. the scientific discipline has its origins in ancient greece with the writings of aristotle and archimedes[1][2][3] (see history of classical mechanics and timeline of classical mechanics). during the early modern period, scientists such as galileo, kepler, and newton laid the foundation for what is now known as classical mechanics. it is a branch of classical physics that deals with particles that are either at rest or are moving with velocities significantly less than the speed of light. it can also be defined as a branch of science which deals with the motion of and forces on objects. the field is yet less widely understood in terms of quantum theory.

explanation:

a saline water is fed to a reverse osmosis unit at flow rate o rotameter connected to reject (retentate) line reads 8 installed in reject and permeate line reads 15.2 milli siemens/cm and 300 micro siemens/com respectively.