Acid-base reactions

Question 1

What is a Brønsted-Lowry base?

Answer 1

A proton acceptor.

Question 2

What is meant by a conjugate acid-base pair?

Answer 2

A pair where the acid donates a proton to form its conjugate base, and the base accepts a proton to form its conjugate acid.

Question 3

What does it mean when we say equilibrium is dynamic?

Answer 3

Both forward and reverse reactions occur simultaneously at equal rates.

Question 4

What is the Law of Mass Action?

Answer 4

k = [products] / [reactants] OR
The rate of a reaction is proportional to the product of the concentrations of the reactants, each raised to the power of their stoichiometric coefficients.

Question 5

How do you write an equilibrium constant expression?

Answer 5

For A + B ⇌ C + D, K = [C][D]/[A][B]

They would then be to the powers of their order within the system

Question 6

What does it mean when K > 1?

Answer 6

The products are favored at equilibrium.

Question 7

What does it mean when K < 1?

Answer 7

The reactants are favored at equilibrium.

Question 8

What is Le Chatelier’s Principle?

Answer 8

If a stress is applied to a system at equilibrium, the system shifts to oppose the change and reestablish equilibrium.

Question 9

How does concentration affect equilibrium position?

Answer 9

Adding reactants shifts equilibrium toward products; adding products shifts it toward reactants.

Question 10

How does pressure affect equilibrium?

Answer 10

In gaseous systems, increasing pressure shifts equilibrium toward the side with fewer gas molecules.

Question 11

How does temperature affect equilibrium?

Answer 11

It depends on whether the reaction is exothermic or endothermic; equilibrium shifts to absorb added heat.

If heated, the system will favour the endothermic direction (where ΔH is positive)

Question 12

What is an acid dissociation constant (Ka)?

Answer 12

A measure of the strength of an acid in solution; high Ka = strong acid.

Question 13

What is a base dissociation constant (Kb)?

Answer 13

A measure of the strength of a base in solution; high Kb = strong base.

Question 14

How are Ka and Kb related?

Answer 14

Ka × Kb = Kw (the ionization constant of water = 1.0 × 10⁻¹⁴ at 25°C)

Question 15

What is pH?

Answer 15

pH = -log₁₀[H⁺]

Question 16

What is pOH?

Answer 16

pOH = -log₁₀[OH⁻]

Question 17

How are pH and pOH related?

Answer 17

pH + pOH = 14

Question 18

What is the pKa?

Answer 18

pKa = -log₁₀Ka; lower pKa = stronger acid

Question 19

What is the pKb?

Answer 19

pKb = -log₁₀Kb; lower pKb = stronger base

Question 20

How are pKa and pKb related?

Answer 20

pKa = pKb = 14

Question 21

How do strong acids behave in water?

Answer 21

They completely dissociate, so [H₃O⁺] = initial acid concentration.

Question 22

How do strong bases behave in water?

Answer 22

They completely dissociate, so [OH⁻] = initial base concentration.

Question 23

How is pH calculated for strong acids?

Answer 23

pH = -log₁₀[H+]

Question 24

How is pH calculated for strong bases?

Answer 24

pOH = -log₁₀[OH-], then pH = 14 - pOH

Question 25

How is pH calculated for weak acids?

Answer 25

Use Ka = [H₃O⁺]² / [HA]; assume [HA]eq ≈ [HA]initial.

Question 26

How is pH calculated for weak bases?

Answer 26

Use Kb = [OH⁻]² / [B]; then find pOH, then pH = 14 - pOH.

Question 27

What is a salt solution?

Answer 27

A solution formed from the neutralization of an acid with a base.

Question 28

What happens when acid + base?

Answer 28

Acid + base --> salt + water

Question 29

Can salt solutions be non-neutral?

Answer 29

Yes, depending on the strength of the acid and base that formed them.

Question 30

What’s the pH of a strong acid + strong base salt?

Answer 30

Neutral, pH ≈ 7

Question 31

What’s the pH of a weak acid + strong base salt?

Answer 31

Basic, pH > 7 (due to conjugate base)

Question 32

What’s the pH of a strong acid + weak base salt?

Answer 32

Acidic, pH < 7 (due to conjugate acid)

Question 33

What are ampholytes?

Answer 33

Substances that can act as both acid and base; e.g., amino acids.

Question 34

What is a buffer solution?

Answer 34

A solution of a weak acid and its conjugate base, or vice versa, that resists changes in pH.

Question 35

How do buffers work?

Answer 35

They neutralize added H⁺ or OH⁻ by reversible reactions with the weak acid/base pair.

Question 36

What equation is used to calculate buffer pH?

Answer 36

Henderson-Hasselbach: pH = pKa + log([A⁻]/[HA])

Question 37

What’s buffer capacity?

Answer 37

The amount of acid or base the buffer can neutralize before a significant pH change.

Question 38

What is the ideal ratio for buffer capacity?

Answer 38

When [A⁻] = [HA], pH = pKa, and buffering is most effective.

Question 39

What happens when a strong acid is added to a buffer?

Answer 39

The base component of the buffer neutralizes the acid, minimizing pH change.

Question 40

What happens when a strong base is added to a buffer?

Answer 40

The acid component of the buffer neutralizes the base, minimizing pH change.

Question 41

What is a titration?

Answer 41

A technique to determine the concentration of an unknown acid or base by neutralizing it with a known solution.

Question 42

What is the endpoint of a titration?

Answer 42

The point at which equivalent moles of acid and base have reacted.

Question 43

What is the equivalence point for strong acid–strong base titration?

Answer 43

pH = 7

Question 44

What is the equivalence point for weak acid–strong base titration?

Answer 44

pH > 7 (due to basic salt)

Question 45

What is the equivalence point for strong acid–weak base titration?

Answer 45

pH < 7 (due to acidic salt)

Question 46

What is an indicator?

Answer 46

A compound that changes color depending on the pH of the solution, used to detect titration endpoints.

Question 47

How do you choose an indicator?

Answer 47

Choose one whose pKa is close to the expected equivalence point pH.

Question 48

What is a Brønsted-Lowry acid?

Answer 48

A proton donor

Question 49

If the [H+] of a solution is 4.2 x10^-4, what equation would you use to find the pH?

Answer 49

pH = -log(4.1x10^-4)

Question 50

If the [H+] of a solution is 4.2 x10^-4, what equation would you use to find the pOH?

Answer 50

pH = -log(4.1x10^-4) Then, subtract the pH from 14 to find the pOH.

Question 51

If the [H+] of a solution is 4.2 x10^-4, what equation would you use to find the [OH-]?

Answer 51

pH = -log(4.1x10^-4) Then, subtract the pH from 14 to find the pOH. Then, [OH-] = 10^-pOH

Question 52

How would you find the [H+] given only the pH?

Answer 52

Use the equation [H+] = 10^-pH

Question 53

How would you find the [OH-] given only the pH?

Answer 53

Use the equation [H+] = 10^-pH Then, use the equation [H+] x [OH-] = 1x10^-14

Question 54

What does pH + pOH equal?

Answer 54

14

Question 55

What do you need to use when dealing with a weak acid?

Answer 55

Ka - dissociation/equilibrium constant

Question 56

How do you find the Ka?

Answer 56

Concentration of products/concentration of reactants Remember to exclude liquids and solids

Question 57

What is Kw?

Answer 57

Ka x Kb 1 x 10^-14

Question 58

What is pKa + pKb?

Answer 58

14

Question 59

How do you find the Ka?

Answer 59

Products over reactants, exclude the solids or liquids

Question 60

What equation would you use to find the [H+] of a weak acid?

Answer 60

[H+] = Square root of Ka.[HA]

Question 61

What can the top of the Ka equation also be looked at as?

Answer 61

[H+]^2

Question 62

Is the conjugate base of a weak acid weak or strong?

Answer 62

Weak

Question 63

What do the parts of the Henderson Hasselbalch equation stand for?

Answer 63

pKa = -logKa [A-] = concentration of conjugate base [HA] = concentration of weak acid