Acids & Bases

Question 1

What is a Bronsted Lowery Acid?

Answer 1

An acid donates the proton or hydrogen ion.

Question 2

What is a Bronsted Lowery Base?

Answer 2

A base accepts the proton or hydrogen ion.

Question 3

What is an amphiprotic species?

Answer 3

Depending on the circumstances they can accept protons or they can donate protons.

Question 4

What is the difference between a weak acid or base and a strong acid or base?

Answer 4

A strong acid or base nearly dissociates 100% of the acid or base whereas a weak acid or base dissociates a very low amount of the acid or base.

Question 5

What is Ka?

Answer 5

The equilibrium constant for the reaction of a Bronsted Lowery Acid that produces H3O+ this is the acid dissociation constant.

Question 6

What is Kb?

Answer 6

The equilibrium constant for the reaction of a Bronsted Lowery Base that produces OH- this is the base dissociation constant.

Question 7

What is Kw?

Answer 7

This is the ionization of water as some water molecules ionize into H3O+ and OH- because of the slight conductivity.

Question 8

What is the small x approximation?

Answer 8

When the initial concentration is much greater than the ka or kb we can assume that the x will not have an effect on the initial concentration. However we must check it by taking the x/initial concentration and it must be less than 5%.

Question 9

What are soluble salts?

Answer 9

These are substances that dissociate 100% in water thus if the ions react with water and form a strong acid or base they will dissociate once more so they do not form a strong acid or base only a weak acid or base.

Question 10

How is the strength of the acid/base related to its conjugate?

Answer 10

The stronger an acid/base the weaker its conjugate acid/base.

Question 11

What is the large X assumption?

Answer 11

If the change in X is small enough to the point where it does not change the initial concentration.

Question 12

How can you tell if you should use the small X assumption?

Answer 12

Ka &laquo_space;Initial concentration

Question 13

What happens when the Ka values are different?

Answer 13

If the Ka values are different observe the higher Ka value that acid is stronger and will dissociate close to 100%.

Question 14

What is a strong base?

Answer 14

1. ) Reacts completely with water and forms HA and OH- ions these are OH’s bound to group 1 or 2 ions.
2. ) Have very large Kb values.

Question 15

What is a strong acid?

Answer 15

1. ) Reacts completely with water and forms A- and H3O+.

2. ) Have very large Ka values.

Question 16

What does no Ka mean?

Answer 16

This means that the Ka value is so large that it has reached completion.

Question 17

What happens to a very weak acid in water?

Answer 17

A very weak acid does not produce H3O+ in water.

Question 18

What is a weak acid?

Answer 18

1. ) Does not react completely with water and forms A- and H3O+.
2. ) Have moderate Ka values.

Question 19

What is a weak base?

Answer 19

1. ) Does not react completely with water and forms HA and OH-.
2. ) Have moderate Kb values.

Question 20

What happens when the concentrations are different?

Answer 20

If there is a large amount of the reactant concentration then there will be a higher concentration of H3O+.

Question 21

What is a % dissociation?

Answer 21

The percentage of the acid or base that dissociates in solution and the percentage is dependent on the strength of the acid or base.

Question 22

How is pKa/Kb related to Ka or Kb?

Answer 22

The smaller the pka/pkb value the larger the ka or kb value which means that the stronger the acid or base respectively.

Question 23

What is a titrant?

Answer 23

This is the known solution in the burette where the identity, volume and concentration are known.

Question 24

What is a titrand?

Answer 24

This is the unknown solution in the beaker where the identity is unknown, volume is known and concentration is unknown. Along with the acid base indicator to tell when the reaction has reached its end. Also water where the concentration does not change but the number of moles do change.

Question 25

What is the half equivalence point?

Answer 25

This is when the number of moles of the weak acid is equal to the number of moles of the conjugate base.

Question 26

What is the equivalence point?

Answer 26

This is when the weak acid has been consumed by the strong base and no more conjugate base can form.

Question 27

What occurs before the equivalence point?

Answer 27

There is excess H3O+ in the solution and the pH can be determined as a result.

Question 28

What occurs at the equivalence point?

Answer 28

The acid is exactly neutralized and the pH > 7 because the substance is basic.

Question 29

What occurs after the equivalence point?

Answer 29

There is excess OH- in the solution and the pH > 7 because the substance is basic.

Question 30

What is the objective at the equivalence point?

Answer 30

To determine the volume of the strong base that is able to consume all of the weak acid and not form anymore conjugate base.

Question 31

Why do na = nOH- = nHAi?

Answer 31

The number of moles of the conjugate base is equal to the number of moles of hydroxide and the acid at the equivalence point because at this point the acid is consumed by the hydroxide entirely and there are no more moles of OH- or HA only A- therefore the A- = OH- = HA.

Question 32

What is the endpoint?

Answer 32

This is the point that can be determined experimentally, visually, and is value dependent on the technique.

Question 33

What is the difference between the equivalence and endpoint?

Answer 33

At the equivalence point there is no more of the limiting reagent, there is an exact amount of titrant that is added, and it is a theoretical point. Whereas the endpoint is This is the point that can be determined experimentally, visually, and is value dependent on the technique.

Question 34

What is a potentiometric titration curve?

Answer 34

Potentiometric titration is a technique similar to direct titration of a redox reaction. It is a useful means of characterizing an acid. No indicator is used; instead the potential is measured across the titrand, typically an electrolyte solution.

Question 35

What are the 4 factors that affect the shape of the titration curve?

Answer 35

1. ) Acid => HA concentration 2. ) Identity 3. ) Base => OH- concentration 4. ) Acid => Volume of the acid

Question 36

What is initial pH affected by?

Answer 36

1. ) The initial concentration of the HA | 2. ) The HA strength

Question 37

What does the equivalence point volume depend on?

Answer 37

1. ) Number of moles of HA | 2. ) Concentration of strong base used

Question 38

What does the equivalent point pH depend on?

Answer 38

1. ) Slightly basic for a weak acid | 2. )The stronger the HA the weaker the conjugate base

Question 39

What does the pH at the half equivalence point depend on?

Answer 39

1.) Strength of HA

Question 40

What if the acid-base indicator ratio is >> 1?

Answer 40

The colour will be the second colour of the indicator.

Question 41

What if the acid-base indicator ratio is << 1?

Answer 41

The colour will be the first colour of the indicator.

Question 42

What if the acid-base indicator ratio is = 1?

Answer 42

The colour will be a mix of the 2 colours present and this means that the pH ~ pKa.

Question 43

What is a buffer?

Answer 43

These are solutions that are able to withstand the addition of a strong acid or base and it must contain similar amounts of both the weak acid and weak base in a conjugate acid/base pair.

Question 44

What is the pH range?

Answer 44

This is the pH range over which a solution is a buffer.

Question 45

What is the buffer ratio?

Answer 45

This is the ratio of conjugate base to weak acid.

Question 46

What are the assumptions that we make?

Answer 46

1. ) The concentration of A- at equilibrium and initially is the same. 2. ) The concentration of HA at equilibrium and initially is the same. 3. ) The HA and A- have the same volume therefore the buffer ratio can be of moles or concentrations.

Question 47

What are the 2 steps that are required to prepare a buffer solution with a target pH?

Answer 47

1. ) Choose the acid that is based on the pka value where the pH is about the same as the pka. 2. ) The buffer ratio is used to adjust the A- and the HA to obtain the correct pH.

Question 48

When does a buffer not work?

Answer 48

The amount of strong acid or base is higher in amount than the weak conjugate acid/base.