Chem Quiz 3 Material

In strong base and weak acid titrations, what is the pH at the 0.5 equivalence point? Is it a buffer?

pH = pKA. Yes, its a buffer

Describe the components of a weak acid/strong base titration curves

What is a titration curve?

A titration curve is a plot of some solution property versus the amount of added titrant. For acid-base titrations, solution pH is a useful property to monitor because it varies predictably with the solution composition and, therefore, may be used to monitor the titration’s progress and detect its end point.

What is the main difference between strong acids and strong bases vs weak acids?

Strong acids and strong bases have complete dissociation, while weak acids must factor in equilibrium

What are the general steps for solving for weak acids/strong bases?

1. Figure out what 1 equivalence is equal to (equal moles of acid + base)

2. Figure out pH before we’ve added any base (weak acid calculation)

3. What happens after we add base (BCA table)

4. After we’ve made the buffered solution, we can use the Henderson-hasselbach equation. We must find the concentration to do this

If the ratio is = 1, what happens to the log X [A-/HA] component of henderson hasselbach?

It becomes 0

When comparing titration curves, the strongest acid will have the highest or lowest pka?

Lowest

Will more base increase or lower pH?

Increase

What are the general steps for ranking titrations in order of increasing pH at the equivalence point of the titration (top=lowest pH and bottom = highest pH)

Describe the components of a polyprotic titrations curve

At equivalence of 1,2, or 3 on a polyprotic titration curve, what is the pH?

The average of pKA1 and pKA2

Where can you use Henderson Hassleback on polyprotic titration graph?

Between 0 and 1, and 1 and 2 equivalence (both halfway points)

How can we get the inital or end pH for polyprotic acids?

The inital is a weak acid equation, but the end can be found through plotting on the pH line and using ka values

In polyprotic acids, when Ka’s get smaller, what 2 important things does that mean

There is smaller amounts of dissociation, and you can treat each dissociation as seperate

How do you know how many equivilance of bases there are?

Depends on how many acidic protons

On a graph, will you usually have flat lines or curves at halfway points? Why?

Flat lines because they represent buffers

When you have questions like this: What do you do?

What happens to the charge at the equivalance and halfway points?

Equiv: Drop by 1

Half: Drop by 0.5

Define protanated?

Transfer of a proton, gaining a positively charged hydrogen ion

At ½ what is pH = to?

pKa

Is a lower pKa acidic or basic?

Acidic

Which proton will be removed first?

The acidic one

What is an equivalent?

Amount of base needed to completely remove H+, anytime pH is below pka, its in the protenated form. Above is deprotenated

When going from A to B drawings, what changes?

You’re just removing the most acidic proton

In amino acids and peptides, how do you know how many equivalence there are?

Based on how many are needed to remove both protons

What does isoelectric mean?

Not charged

How do you know if something is in its acidic or basic form?

If the pH>pKa (by 2 or more units) the base form will dominate. If pH < pKa, the acid does

What will OH- always interact with?

The best acid

How do you know what one equivalent is equal to?

The moles

What is A- and HA in the henderson hasslebach?

A- is the base and HA is the acid

What is the halfway point pH equal to?

pKA

Anytime that a weak acid is titrated with a strong base, will pH (at equivalence) be greater or less than 7?

Greater

At equivalence, its equal ___ of acid and base

Moles

At the equivalence point, what is equal?

Acid = base

What is 1 equivalent = to?

Moles of acid/ base in original solution

At the halfway point, what is ph = to?

pka

If you’re comparing endpoint pH’s, what do you do?

At endpoint only the conjugate is left, so you can rank based onka/kb to see which has the highest/lowest pH. If its being titrated with strong acid it will be Ka, strong base will be Kb

How do you know how many equivalence are needed?

Depends on how many pkas are given in the problem

WIll there be OH- or H3O+ at the third equivalence point?

No, you’ve used all the strong acid and base by that point

How do you decide which pka to use?

Look back at the titration curve

How do you know when to stop using a bca table and start using an ice table

When the strong acid or base has run out