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BS11001-Biomolecules > pH, pK and Buffers > Flashcards

pH, pK and Buffers Flashcards

1
Q

What is an Acid?

A

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

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2
Q

What is a Base?

A

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

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3
Q

What do acids and bases operate in?

A

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

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4
Q

What is an amphoteric compound?

A

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

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5
Q

What does a strong acid dissociate to form?

A

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

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6
Q

What does a weak acid not do very well?

A

A weak acid does not dissociate to a very great extent

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7
Q

What does a strong base readily accept?

A

A strong base readily accepts a hydrogen ion from solution

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8
Q

What does a weak base not readily accept?

A

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

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9
Q

What do strong acids have?

A

Strong Acids have weak conjugate bases

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10
Q

What do weak acids have?

A

Weak acids have strong conjugate bases

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11
Q

How do you calculate the Ka?

A

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

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12
Q

A strong acid has a what Ka value?

A

Large

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13
Q

A weak acid has a what Ka value?

A

Small

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14
Q

How do you calculate the Kb

A

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

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15
Q

A strong base has what Kb value?

A

Large

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16
Q

A weak base has a what Kb value?

A

Small

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17
Q

How do you calculate the pKa?

A

pKa = -log(Ka)

Log is to the base 10

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18
Q

How do you calculate the pKb?

A

pKb = -log(Kb)

Log is to the base 10

19
Q

Does water undergo dissociation?

A

Yes, but only to a very small degree

20
Q

What is the ion product of water?

A

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

21
Q

How do you calculate the pH?

A

pH = -log[H3O+]

Log is to the base 10

22
Q

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

A

Acidic solution

23
Q

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

A

Basic solution

24
Q

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

A

Neutral Solution

25
Q

What is equal in a neutral solution?

A

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

26
Q

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

A

1x10^-14 at 25 degrees celsius

27
Q

How do you calculate the pH of a strong acid?

A

pH = -log (concentration of initial solution)

28
Q

The Henderson-Hasselbach equation links what?

A

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

29
Q

What is the Henderson-Hasselbach equation?

A

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

30
Q

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

A

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

31
Q

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

A

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

32
Q

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

A

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

33
Q

What does the pKa value of a molecule represent?

A

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

34
Q

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

A

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

35
Q

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

A

pH = 14 - pOH

36
Q

How do you calculate the pOH?

A

pOH = -log [OH]

37
Q

How do you calculate the concentration of hydronium ions?

A

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

38
Q

How do you calculate the concentration of hydroxide ions?

A

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

39
Q

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

A

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

40
Q

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

A

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

41
Q

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?

A

Convert the equation into the quadratic formula

([H3O+]^2) + Ka[H3O+] - Ka[HA] = 0
a = 1, b = Ka, c = Ka

42
Q

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?

A

Convert the equation into the quadratic formula

([OH-]^2) + Kb[OH-] - Kb[B] = 0
a = 1, b = Kb, c = Kb

43
Q

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

A

Ka = 10^-pKa

44
Q

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

A

Kb = 10^-pKb

BS11001-Biomolecules (5 decks)

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