Chap 14 - Acid/Base Equilib

Based on the Kb values, which of the following corresponds to the strongest base?

0.07 Stronger bases have greater Kb values. The largest Kb value is 0.07, so it corresponds to the strongest base

In a buffer solution made from acetic acid and the acetate ion, once the acetic acid concentration drops to 10% of the acetate ion, the pH will quickly shift by what amount?

1 Assume that the initial pH is equal to the pKa. The Henderson-Hasselbalch equation is the following. pH=pKa+log[base][acid] Since the acid drops to 10% of the acetate ion, the equation can be written as follows. pH=pKa+log[100][10] pH=pKa+log(10) pH=pKa+1 The pH will climb 1 unit.

Which solution has the greatest buffer capacity?

1 mole of acid and 1 mole of base in a 1.0 L solution A buffer that is 1 M in acid and base will have the greatest concentration of buffer, and therefore the greatest buffer capacity.

Which pH value corresponds to the highest concentration of hydronium?

1.2 (low Level numbers)

A buffer solution has equal concentrations of acetic acid and the acetate ion and has a pH that is initially 4.74. What percentage must the acetic acid concentration decrease by to result in a pH increase of one unit?

10 Initially at pH 4.74, the pH of this buffer solution will rapidly climb by at least 1 pH unit if the acetic acid concentration dips below 10% of the acetate ion concentration.

A buffer solution will lose its buffer capacity when one of the components drops below:

10% of the conjugate Once the concentration of one of the substances in the buffer drops below 10% of the other, the solution will begin to lose much or most of its buffer capacity.

Which of the following Ka values corresponds to the strongest acid?

4.1×10−3

Which of the following is most likely to be a good buffer mixture?

50 mL of 1 M acid and 50 mL of 1 M conjugate base A good buffer will have relatively equal concentrations of the acid or base and its conjugate. Equal volumes of solutions at identical concentration will ensure that the species are in a 1:1 ratio.

Which description best fits the definition of a buffer?

A buffer is a mixture of a weak acid or a weak base and its conjugate.

All of the following are true of acid-base neutralization, EXCEPT

A neutral solution is always formed when stoichiometrically equivalent amounts of an acid and a base are mixed.

Of the following, which is not a triprotic acid?

CH3CO2H

Which is a possible example of species that can comprise a buffer solution?

CH3COOH and NaCH3COO

Choose the option below that forms a weakly basic solution. Assume all acids and bases are combined in stoichiometrically equivalent amounts.

H2CO3(aq)+Ca(OH)2(aq)⇌CaCO3(aq)+2H2O(l)

Which of the following combinations would make the best buffer?

H3PO4 and NaH2PO4 A buffer is a mixture of a weak acid or a weak base and the salt of its conjugate, such as H3PO4 and NaH2PO4.

Which is an example of a monoprotic acid that is NOT a binary compound?

HNO3

Which of the following statements regarding the buffer capacity of a buffer system are true?

If enough strong base is added to a buffer to react with all of the weak acid present, the buffer can no longer neutralize additional amounts of base, and the pH will dramatically increase. Increasing in the concentration of weak acid and its conjugate base will increase the buffer capacity of a solution.

In order for the pH of a solution to equal the pKa of an acid, what must be true about the solution?

In order for pH to equal the pKa of the acid, the last term in the Henderson-Hasselbalch equation must be equal to zero. This will only happen if [A−]=[HA]: the quotient [A−][HA] will equal 1, thus its logarithm will equal zero.

Why is the conjugate acid of a strong base (like NH−2) negligible when determining pH?

It is too weak to produce an appreciable amount of hydronium ions.

Which acid/base pair will give an equivalence point that cannot be predicted solely by a general knowledge of acid and base strength?

NH3 and CH3COOH If titrating a weak acid with a weak base, the equivalence point could have a variety of pH values

If we add acid to a buffer containing NaCH3CH2COO and CH3CH2COOH, the acid will react with which of the following?

NaCH3CH2COO The H+ ions dissociated from the acid will react with the propanoate (CH3CH2COO−) ions to form more CH3CH2COOH and water, thereby neutralizing the acid with relatively little change in the pH of the solution.

Which of the following pairs of species would generate a salt derived from a weak acid and a weak base?

NaNO2 and H2CO3

Which of the following gives the definition of percent ionization of a weak acid?

Percent ionization is the ratio of the concentration of the ionized acid at equilibrium to the initial acid concentration times 100%.

What will determine the number of moles of hydronium in an aqueous solution of a strong monoprotic acid?

The amount of acid that was added.

Consider two acids with the same starting concentrations, one strong and one weak. Each is titrated by a strong base. How do the titration curves compare?

The titration curve of the weak acid will begin at a higher pH but the curves will end up at the same pH levels far beyond the equivalence point.

Percent ionization for an aqueous acid can be expressed as:

[H3O+]eq/[HA]i×100%, where "eq" stands for equilibrium and "i" stands for initial

A stronger base will correlate with:

a higher Kb and a higher percent ionization

A strong base will be associated with

a large Kb value and a large percent ionization A strong base will be associated with a large Kb value and a large percent ionization.

A weak base has

a low percent ionization and a small Kb

In a buffer solution made of acetic acid and sodium acetate, any base that is added will react primarily with which of the following?

acetic acid

A buffer solution with pH around 9 may contain which of the following?

ammonia

Which of the following will exhibit the greatest change in pH when 1.0 mL of 1M HCl is added to it?

an unbuffered aqueous solution

Which is the acid responsible for the buffering capacity of blood?

carbonic acid Carbonic acid and the bicarbonate ion are responsible for maintaining the pH of the bloodstream.

For acid-base conjugate pairs, greater values of Ka

correspond to lower values of Kb

The Henderson-Hasselbalch equation is useful for:

determining concentrations of buffer components for a target pH.

A strong acid will _________ increase a solution's concentration of ________

dramatically; hydronium

Which of the following is NOT a strong acid?

hydrofluoric acid

An Arrhenius base will

increase hydroxide concentration in solution

On a titration curve, the equivalence point is always a(n):

inflection point

When titrating a weak acid with a strong base that have the same concentration, the equivalence point will have a pH that:

is always above 7 The pH at the equivalence point of a weak acid and a strong base will be greater than 7,

If the concentrations of the acid and conjugate base in a buffer are equal, what will be true about the pH of a solution?

it will be equal to the pKa of the acid If these two concentrations are the same, the ratio [A−][HA] the Henderson-Hasselbalch equation will be equal to 1. The logarithm of 1 is always 0, leaving us with pH=pKa, so the pH of such a solution will always be equal to the pKa of the acid.

Assuming a buffer solution is made with equal concentrations of an acid and its conjugate base,the Henderson-Hasselbalch equation allows us to select a substance for a buffer solution at a specific pH on the basis of its

pKa

A weak acid will _____ increase a solution's concentration of ______

slightly; hydronium

When a moderate amount of a weak acid is placed in aqueous solution, which of the following will be present in the greatest concentration?

the nonionized acid If an acid is weak, it will only ionize to a very small extent, forming the hydronium ion and conjugate base in only negligible amounts relative to the concentration of nonionized acid.

When the ionization reaction of a weak base is at equilibrium

the rates of the forward and reverse reactions will be equal

When a weak base is placed in aqueous solution, which of the following will be present in the greatest concentration?

unionized base