Unit 5 Salts, Buffers, and Titrations Mastery Quiz

Strong acids/bases form _______ conjugates

weak conjugates

Weak acids/bases form ______ conjugates

strong conjugates

Buffer systems can do what?

Resist changes in pH due to the presence of both an acid and its conjugate base being able to react with additional H+ and OH-

If HA and A- are both initially present, what will happen what will happen when an acid vs. base is added?

HA can consume base when added

A- can consume acid when added

If BH and B are both initially present, what will happen when an acid vs. base is added?

B can consume acid when added

BH can consume base when added

How can buffers be made?

By directly mixing week acid/base and strong conjugate

or

by indirect reactions that produce the conjugate without fully consuming the weak acid/base

In buffer systems, pH=pKa when

[HA] = [A]

In buffer systems, pOH = pKb when

[B] = [BH]

What is the half equivalence point?

When [HA] = [A] or [B] = [BH] and pH = pKa or pOH = pKb

What is the concentration of substances at half equivalence?

Half of the species of solution exist in their acid/base form and half exist in their conjugate form so there is half of the acid/base left from the beginning

if HA > A then

pH < pKa (more acidic)

HA < A then

pH > pKa (more basic)

What is buffering capacity?

The point at which the buffered solution will be overwhelmed and not be able to resist pH changes

Equation for buffer solutions for acids:

pH = pKa + log ([A]/[HA])

Equation for buffer solutions for bases:

pOH = pKb + log([BH]=[B])

Buffers are always a ratio of the ____ to _____

conjugate /acid or base

What happens when the ratio of [A]/[HA] or [BH]/[B] changes?

it disrupts the pH/pOH

if [B] > [BH] then

pOH > pKb

if [B] > [BH] then

pOH < pKb

Analyte

the unknown concentration

Titrant

the known )standardized) concentration

Indicator

used to visually determine the equivalence point and selected based on expected equivalence pH

Combing a strong acid + strong base results in:

• formation of a weak conjugate ( no hydrolysis)

• equivalence pH = 7

• Both the acid and base are fully consumed at equivalence

Combing weak acid and strong base results in :

• creates a strong conjugate base of the weak acid

• results in hydrolysis

• at equivalence both the acid and base are fully consumed

• Equivalence pH > 7

Combining strong acid and weak base results in:

• results in a strong conjugate acid of the weak base

• results in hydrolysis

• at equivalence both the acid and base are fully consumed

• the equivalence point has a pH < 7

When looking at a titration curve, look for:

• starting pH

• strong or weak based on curve

• pH of equivalence point

• Buffered/non-buffered solution

pKa occurs ______ to equivalence point and can be used to identify the ______

halfway; acid

on titration curve, [A] = [HA] occurs when

it is halfway to the equivalence point

Buffer:

solution containing partially reacted acid and its conjugate base (pH = pKa + log… only applies to buffers)

How do you identify conjugate when there are no acids/bases present?

Break the equation into separate equations, one for each reactant to show what each is being broken in to. Then identify if there are any strong conjugate present

How do you determine the effect a strong conjugate has on the reaction?

If it is a strong conjugate base, it will increase pH as it results in the formation of OH, lowering the acidity

If it is a strong conjugate acid, it will decrease pH as it will result in the formation of H, increasing the acidity

If K >> 1 and M is the molarity of the starting substance(acid or base), whst is the concentration of the products

Each product will have a concentration of M as the reaction is highly favorable and is therefore assumed to go to completion

What are all 6 of the strong acids?

HCl, HBr, HI, HNO3, H2SO4, HClO4

K forward =

1/K reverse

What point is the best for determining whether the acid/base is strong or weak on a titration curve?

The equivalence point (remember difference strength acid + base combos) and (but less helpful) the half equivalence point as this is where pH = pKa

What regions on a titration cure represent buffering?

The relatively flat regions of the curve(both before and after the equivalence point); ;these regions contain both the weak acid and conjugate base

After which point is the acid primarily in its deprotonated form?

After the equivalence point

At which point on a titration curve can the pH of the acid/base be determined?

At the half equivalence point as this is where pH = pKa as there are equal concentrations of acid and conjugate base at half equivalence

At which point on the titration curve can you determine Ka?

At the half equivalence point

In acids, what determines how strong of an acid it is(thing HX, what kind of bond strength)

The HX bond; the weaker this bond is, the easier it is to donate H+ and therefore the stronger the acid; the less electronegative the A in HA the weaker the bond and the more acidic

What is the effect of adding more Oxygen atoms to acids?

The more oxygen atoms, the more atoms to split the IMFs between and therefore the weaker the bond to the H+ ion, making it easier to donate H+, and therefore a stronger acid

The _______ the Ka of an acid, the _____ the acid

greater; stronger

How do you find pH at equivalence of a titration?

Find the moles of acid/base being reacted, then use this to calculate the molarity of the conjugate being produced based on the new volume of the solution at equilibrium. Then set up the hydrolysis reaction of the conjugate and solve for the concentration of [OH] or [H] based on if it is an acid or base. From there solve for pOH/pH.