pH, pK and Buffers

Question 1

What is an Acid?

Answer 1

An acid is a hydrogen ion donor: a hydrogen ion is generated when an acid dissociates

Question 2

What is a Base?

Answer 2

A base is a hydrogen ion acceptor: it removes a hydrogen ion from solution

Question 3

What do acids and bases operate in?

Answer 3

Acids and bases operate in pairs: an acid must have a base to which it donates a hydrogen ion

Question 4

What is an amphoteric compound?

Answer 4

An amphoteric compound is one that can act as either an acid or a base

Question 5

What does a strong acid dissociate to form?

Answer 5

A strong acid readily dissociates to form its conjugate base when dissolved in water, releasing a hydrogen ion in the process

Question 6

What does a weak acid not do very well?

Answer 6

A weak acid does not dissociate to a very great extent

Question 7

What does a strong base readily accept?

Answer 7

A strong base readily accepts a hydrogen ion from solution

Question 8

What does a weak base not readily accept?

Answer 8

A weak acid does not readily accept a hydrogen ion from solution

Question 9

What do strong acids have?

Answer 9

Strong Acids have weak conjugate bases

Question 10

What do weak acids have?

Answer 10

Weak acids have strong conjugate bases

Question 11

How do you calculate the Ka?

Answer 11

The Ka is calculated by;
Multiplying the concentration of Hydronium ions with the concentration of the acids conjugate base pair
Then, divide by the concentration of the acid

Question 12

A strong acid has a what Ka value?

Answer 12

Large

Question 13

A weak acid has a what Ka value?

Answer 13

Small

Question 14

How do you calculate the Kb

Answer 14

The Kb is calculated by;
Multiplying the concentration of BH+ with the concentration of hydroxide ions
Then, divide by the concentration of the base

Question 15

A strong base has what Kb value?

Answer 15

Large

Question 16

A weak base has a what Kb value?

Answer 16

Small

Question 17

How do you calculate the pKa?

Answer 17

pKa = -log(Ka)

Log is to the base 10

Question 18

How do you calculate the pKb?

Answer 18

pKb = -log(Kb)

Log is to the base 10

Question 19

Does water undergo dissociation?

Answer 19

Yes, but only to a very small degree

Question 20

What is the ion product of water?

Answer 20

Kw = [H3O+] [OH-] = 1x10^-14 at 25 degrees celsius

Question 21

How do you calculate the pH?

Answer 21

pH = -log[H3O+]

Log is to the base 10

Question 22

If the pH is less than 7, then what type of solution do you have?

Answer 22

Acidic solution

Question 23

If the pH is greater than 7, then what type of solution do you have?

Answer 23

Basic solution

Question 24

If the pH is equal to 7, then what type of solution do you have?

Answer 24

Neutral Solution

Question 25

What is equal in a neutral solution?

Answer 25

In a neutral solution, the concentrations of [H3O+] and [OH-] are equal

Question 26

What value is given when you multiply the concentration of hydronium ions with the concentration of hydroxide ions at 25 degrees Celsius?

Answer 26

1x10^-14 at 25 degrees celsius

Question 27

How do you calculate the pH of a strong acid?

Answer 27

pH = -log (concentration of initial solution)

Question 28

The Henderson-Hasselbach equation links what?

Answer 28

The Henderson-Hasselbach equation links the pH and pKa of a weak acid solution to the concentration of acid and base present.

Question 29

What is the Henderson-Hasselbach equation?

Answer 29

pH = pKa + log(concentration of conjugate base pair divided by the concentration of the acid)

Question 30

Does a neutralization always result in a solution with a neutral pH?

Answer 30

No. A neutralization reaction only results in a neutral solution if the reaction involves the salt of a strong acid and a strong base

Question 31

A stronger acid is most likely to be ionized in what?

Answer 31

A stronger acid is most likely to be ionized in aqueous solution than a weaker one, and therefore to partition into an aqueous phase

Question 32

A weaker acid is more likely not to be ionized which causes what?

Answer 32

A weaker acid is more likely not to be ionized, and therefore to partition into a hydrophobic/lipophilic phase

Question 33

What does the pKa value of a molecule represent?

Answer 33

The pKa value of a molecule represents the pH at which it is 50% dissociated in solution

Question 34

The pH value around which a solution buffers is equal to what?

Answer 34

The pH value around which a solution buffers is equal to the pKa of the acid

Question 35

How do you calculate the pH once a strong base completely dissociates?

Answer 35

pH = 14 - pOH

Question 36

How do you calculate the pOH?

Answer 36

pOH = -log [OH]

Question 37

How do you calculate the concentration of hydronium ions?

Answer 37

Square root; Ka multiplied by the concentration of the Acid(at time zero)

Question 38

How do you calculate the concentration of hydroxide ions?

Answer 38

Square root; Kb multiplied by the concentration of the Base(at time zero)

Question 39

What conditions must be met to use case one when calculating the pH of a solution of a monoprotic weak acid?

Answer 39

The concentration of the acid > 10^-3 AND The Ka < 10^-3

Question 40

What conditions must be met to use case one when calculating the pH of a solution of a monoprotic weak base?

Answer 40

The concentration of the base > 10^-3 AND The Kb < 10^-3

Question 41

What must you do if the conditions are not met to use case one when calculating the pH of a solution of a monoprotic weak acid?

Answer 41

Convert the equation into the quadratic formula ([H3O+]^2) + Ka[H3O+] - Ka[HA] = 0 a = 1, b = Ka, c = Ka

Question 42

What must you do if the conditions are not met to use case one when calculating the pH of a solution of a monoprotic weak base?

Answer 42

Convert the equation into the quadratic formula ([OH-]^2) + Kb[OH-] - Kb[B] = 0 a = 1, b = Kb, c = Kb

Question 43

How do you calculate the Ka of a weak acid when given the pKa?

Answer 43

Ka = 10^-pKa

Question 44

How do you calculate the Kb of a weak base when given the pKb?

Answer 44

Kb = 10^-pKb