Acid Base Equalibria

Question 1

What are Bronsted Lowry acids? (1)

Answer 1

• Proton donors (1)

Question 2

What are Bronsted Lowry bases? (1)

Answer 2

• Proton acceptors (1)

Question 3

What is produced when an acid reacts with water? (2)

Answer 3

• Hydrogen ions in the form of
  Hydroxonium ions (H3O+) (1)
• (A-) A negative ion (1)

Question 4

What is produced when a base reacts with water? (2)

Answer 4

• Hydroxide ion (1)
• (BH+) A positive ion (1)

Question 5

What’s the difference between weak and strong acids/bases? (1)

Answer 5

• Strong acid/bases ionise almost
  completely (1)
• Weak acid/bases partially
  ionises (1)

Question 6

What is a weak acid? (3)

Answer 6

• Backwards reaction favored (1)
• Not many H+ produced (1)
• Examples being carboxylic acids (1)

Question 7

What is a strong acid? (3)

Answer 7

• Forward reaction favored strongly
  (1)
• Lots of H+ produced (1)
• Examples being
  hydrochloric/sulfuric/nitric acid (1)

Question 8

What is a weak base? (3)

Answer 8

• Backward reaction favored (1)
• Not many OH- produced (1)
• Example being ammonia (1)

Question 9

What is a strong base? (3)

Answer 9

• Forward reaction favored (1)
• Lots of OH- produced (1)
• Examples being group 1 hydroxides
  (1)

Question 10

Acids and bases react to form what? (2)

Answer 10

• Water molecule (1)
• pH neutral salt (1)

Question 11

What is the exception to the acid base reaction? (3)

Answer 11

• Ammonia doesn’t produce OH- (1)
• Ammonium ions (NH4)x is produced
  (1)
• No water (1)

Question 12

Why is the enthalpy change of neutralization similar in all strong acids/bases? (2)

Answer 12

• There is no enthalpy of dissociation
  involved (1)
• Since strong acids/bases will fully
  ionise (1)

Question 13

What are the 2 types of enthalpy involved in neutralisation of weak acids/bases? (2)

Answer 13

• Enthalpy of dissociation (1)
• Enthalpy when H+ and OH-
  reacts (1)

Question 14

What is the pH equation? (1)

Answer 14

pH = -log(H+)

Question 15

What is the equation for the concentration for H+? (1)

Answer 15

[H+] = 10−pH

Question 16

What is meant by polyprotic? (3)

Answer 16

• When acids donate more than
  one proton (1)
• Diprotic is where one mole of
  acid produces 2 moles of H+ (1)
• Triprotic is where one mole of
  acid produces 3 moles of H+ (1)

Question 17

How would you calculate the pH of a strong acid? (3)

Answer 17

• Concentration of acid is the
  same as H+ (1)
• Since we assumes it ionises
  fully (1)
• Multiply concentration if
  polyprotic (1)

Question 18

How do you calculate the pH for a strong base? (2)

Answer 18

• Add values to the expression:
  Kw = [H+][OH-] (1)
• Find H+ and add to the
  formula: -log[] (1)

Question 19

How do you calculate the pH for a weak acid? (2)

Answer 19

• Add values to the expression:
  Ka = [H+]^2 / Acid (1)
• Find H+ and add to the
  formula: -log[] (1)

Question 20

How do you calculate the concentration for a weak acid? (3)

Answer 20

• Add pH to the formula:
  -log[] (1)
• Add to [H+] in the expression:
  Ka = [H+]^2 / Acid (1)
• Find Acid (1)

Question 21

What is the expression for pure water? (2)

Answer 21

• Kw = [H+]^2 (1)
• Because there is an equal
  concentration of H+ and OH-
  (1)

Question 22

How is pKw calculated? (2)

Answer 22

-log[Kw] (1)

This displays Kw at a smaller scale to make easier to use (1)

Question 23

How is pKa calculated? (2)

Answer 23

-log[Ka] (1)

This is an alternate method for measuring acid strength (1)

Question 24

How is pH measured during experiments? (2)

Answer 24

• Use of pH probe (1)
• Distilled water resetting pH to
  7.0 (1)

Question 25

How do you calculate Ka with mass and pH? (4)

Answer 25

- Work out moles: = Mass/Mr (1) - work out concentration: = moles / vol(dm) (1) - Calculate [H+] with: -log[] - Substitute into expression: Ka = [H+]^2 / Acid (1)

Question 26

What happens when acids are diluted? (2)

Answer 26

- Concentration of [H+] decrease (1) - pH will increase (1)

Question 27

What is the purpose of titration? (1)

Answer 27

- To work out the concentrations of an acid/base (1)

Question 28

How are titrations carried out? (2)

Answer 28

- Have an acid/base with known concentration in the burette (1) - Add to the conical flask with no known concentration until colour change (1)

Question 29

What are the titration curves? (2)

Answer 29

- S shaped (1) - Will be longer the stonger the acid/base (1)

Question 30

What is the equivalence point on the titration curve? (2)

Answer 30

- Sharp vertical rise on the curve (1) - At this point the acid has been fully neutralised by the base (1)

Question 31

What is the half neutralisation point? (2)

Answer 31

- The point half way between zero and the equivalence point (1) - Here is where: pH = pKa (1)

Question 32

What are the two common indicators used in titrations? (6)

Answer 32

- Methyl Orange (1) - Red at low pH and Yellow at high pH (1) - Used for strong acid titrations (1) - Phenolphthalein (1) - Colourless at low pH and Pink at high pH (1) - Used for weak acid/strong base titrations (1)

Question 33

What indicator do we use for weak acid/weak base titrations? (2)

Answer 33

- Use a pH meter instead (1) - Since there is no sharp pH change present (1)

Question 34

How do you calculate titrations? (4)

Answer 34

- Write a balanced equation (1) - Calculate the number of moles: = Concentration x Volume(Dm3) (1) - Find the molar ratio using the equation (1) - Calculate the volume: = (Moles/Conc) x 1000 (1)

Question 35

What is an acidic buffer? (3)

Answer 35

- Resists pH change to keep solution below pH 7 (1) - They are made from EXCESS of: - Weak Acid (1) - Its conjugate base (1)

Question 36

Explain how acidic buffers work with Ethanoic acid and Sodium ethanoate (5)

Answer 36

- 2 equilibrium equations co exist in the same beaker (1) - The conjugate base (Sodium Ethanoate) reacts with added H+ (1) - Equilibrium shifts to the left as more acid is produced (1) - The weak acid (Ethanoic acid) reacts with added OH- (1) - Equilibrium shifts to the right to replace the H+ (1)

Question 37

Where is the evidence of buffer action on a titration curve? (1)

Answer 37

- Flat line on curve before the equivalence point (1)

Question 38

How are buffers used in blood? (3)

Answer 38

- CO2 breathed out reduces levels of carbonic acid (1) - Equilibrium shifts to right to replace the acid and increases H+ production (1) - Hydrogencarbonate ions will react with H+ to control blood pH (1)

Question 39

How would you work out the Ka value in a titration curve? (2)

Answer 39

- Find pKa value from half equivalent point (1) - Ka = 10^-pKa (1)