L04: Acids, Bases, pH, and Buffers

Question 1

Which two ions form when a water molecule ionizes?

Answer 1

A water molecule can ionize into ions when one polar bond to Hydrogen breaks. It’s break into two pieces; Hydrogen Ions (H+) and Hydroxide Ions (-OH).
The free proton (H=) may associate with a H20 molecule to form Hydronium ion (H30+).
It also may associate with solute molecules resulting in important biological chemistry (e.g., change in protein shape, change in pigment coloration).

Question 2

How does the concentration of these two ions compare in pure water (pH=7)? Why does this equality exist? Why should biologists care about the concentrations of these ions in solution? What is the concentration (in Molarity) of these two ions in pure water (pH=7)?

Answer 2

In pure water (no pure water in nature), the concentration of Hydrogen Ions (H+) with be equal to Hydroxide Ions (-OH) because each H20 has both H and OH.
They are bioactive and changes in their concentration impact numerous biological phenomena such as: breathing, enzyme action, coloration, etc.

The concentration of H+ and -OH in pure water is (the same):
[H+] = 10^-7 M (0.0000001 mols of H+ in 1 L H20)
[-OH] = 10^-7 M (0.0000001 mols of -OH in 1 L H20)

Question 3

What happens to the concentration of H+ in a solution in which an acid has been added? How does this change impact the relationship between H+ and –OH in the solution?

Answer 3

Body fluids are not pure water; they possess solutes.
If solutes act as acids or bases this causes [H+] to NOT equal [-OH]. Adding an acid to water increases [H+] in solution. adding an acid to water/aqueous solution [H+] > [-OH]

Question 4

What is the difference between a strong acid and a weak one? How can you tell if a chemical reaction involves a strong or weak acid? How does adding an acid to a solution impact the pH of the solution?

Answer 4

Strong acids are those that completely dissociate in aq. ex: HCI will dissociate into ions when put into water. (a single arrow indicates the rxn only proceeds one way).
Weak acids may only partially dissociate in aq. (the double arrow indicates indicates the molecules can re-associate).
The more H+ a solution has is the lower pH value it’ll have.

Question 5

What is a Brønsted-Lowry Base?

Answer 5

They attach to free H+ (protons) already present in aq. (from ionization of water or acids) decreases [H+] in solution.

Question 6

What happens to the concentration of H+ in a solution in which a Brønsted-Lowry Base has been added? How does this change impact the relationship between H+ and –OH in the solution?

Answer 6

Adding a brønsted-lowry base decreases the concentration of H+ in a solution. The relationship between H+ and -OH in a solution with brønsted-lowry base is [H+] < [-OH].

Question 7

What happens to the concentration of –OH in a solution in which a Brønsted-Lowry Base has been added?

Answer 7

It increases because H+ are decreasing

Question 8

What is a Hydroxide base?

Answer 8

release -OH/hydroxide ion into solution so it increases [-OH] in solution

Question 9

What happens to the concentration of –OH in a solution in which a hydroxide base has been added? How does this change impact the relationship between H+ and –OH in the solution? What happens to the concentration of H+ in a solution in which a Hydroxide base has been added?

Answer 9

increases the amount of -OH. The relation it creates is [H+] < [-OH]. The concentration of H+ decreases.

Question 10

What is the difference between a strong base and a weak one? How can you tell if a chemical reaction involves a strong or weak base? How does adding a base to a solution impact the pH of the solution?

Answer 10

A weak base is one that only partially dissociates to give ions in solution. A strong base is one that fully dissociates to give ions in solution.
Adding a base to a solution makes it more alkaline (8-14).

Question 11

What does pH mean? What is the equation used to determine pH?

Answer 11

pH (power of hydrogen) is an easier way to report the wide range of [H+] in aqueous solutions using a simple scale from 0 to 14. The equation is pH = -log[H+]

Question 12

What does it mean that the pH scale is an inverse scale? What does it mean that the pH scale is a log scale?

Answer 12

Inverse means greater [H+] correspond with lesser pH values on the pH scale. The pH scale is logarithmic, meaning that an increase or decrease of an integer value changes the concentration by a tenfold. For example, a pH of 3 is ten times more acidic than a pH of 4.

Question 13

Which pH value corresponds with the greatest concentration of H+? Which pH value corresponds with the least concentration of H+? Can you compare H+ concentration in solutions of variable pH?

Answer 13

greatest concentration of H+ pH value - 0
least concentration of h+ pH value - 14
yes you can compare different acidic (0-6) /neutral (7) /alkaline (8-14) solutions. The difference of values corresponds with a 10-fold change.

Question 14

What is a buffer? What are most buffers?

Answer 14

Buffers are solutes in aq. that resist changes in pH of the solution by associating/dissociating with H+
Most buffers are weak acids (and their conjugate bases)

Question 15

How does the carbonic acid-bicarbonate buffer system work in our blood?

Answer 15

When your blood begins to acidify during acidosis, the
additional H+ associate with HCO3– preventing significant
build up of H+ in aq. and a further ↓ in pH (homeostasis).

During alkalosis, additional H+ are liberated during the
dissociation of H2CO3 to fill the H+ deficit (homeostasis).

Question 16

Which direction must the reaction precede to stabilize blood pH when an Acid is entering the blood? Which direction must the reaction precede to stabilize blood pH when a Brønsted-Lowry Base is entering the blood? In either case, can you explain how the buffer stabilizes [H+]?

Answer 16

reaction proceeds to left if pH decreases (H+ increases); rxn ← if pH ↓ (i.e., [H+] ↑ during acidosis)

reaction proceeds to right if pH decreases (H+ decreases); rxn → if pH ↑ (i.e., [H+] ↓ during alkalosis)

When acid enters the body, the H+ forms a molecule with bicarbonate to form carbonic acid that’ll maintain body pH. When BLB enters the body and attaches to a H+, a carbonic acid will dissociate to make up for the H+.

Question 17

What is an acid?

Answer 17

Acids release H+ into solution by ionizing a bond to a H.
Adding an acid to water ↑ [H+] in solution.

Question 18

Why is regulating the pH of the blood important?

Answer 18

Activity of most chemical reactions via enzyme proteins is dependent on fluid pH. Disruption in your acid-base balance can lead to medical conditions known as acidosis and alkalosis.