Homework 2 question 9 and 10

[705925790]

I am looking over past assignments and I am still confused on how the pKa and pH relationship shows whether a mixture is charged or not. Can someone explain?

[Ethan Crofut 1E]

When pH = pKa, 50% of an acid will be undissociated and the other 50% will have dissociated; if it's a base, 50% will be protonated and the other 50% not protonated. Basically, the conjugates have equal concentrations.

That means, adjusting the pH to a value that is not pKa will cause the concentration of one of the conjugates to be more than the other. Often in these examples, one of the conjugates is charged but the other isn't; for example we would consider CH3COOH to be uncharged and CH3COO- to be charged, and depending on which one has the higher concentration, we would be able to determine whether or not the charged species (CH3COO-) dominates, aka has more than 50% concentration.

In terms of solving the problems, low pH = high concentration of protons = species will tend to be protonated, as increasing the amount of protons will shift the reaction to one side or the other if you look at the chemical equation. Acids will be mostly undissociated, and bases will be more than 50% protonated.

The opposite would be true for high pH.

[305568482]

pKa show if an acid is strong or weak, while pH shows if a system is acidic or alkaline. If for example the pKa of of an acid is low then it is a strong acid and if the pKa of an acid is high then the acid is weak. If the pH of a system is high then the system as a whole is alkaline and if it low then the system is acidic. the pH of solution is larger/ greater than the pKa then the group is deprotonated. If the pH of solution is smaller/less than the pK then the group is protonated.