5.1.3 - Acid, Bases and Buffers

Question 1

What is a bronsted -Lowry acid ?

Answer 1

A species that donates a proton

Question 2

What s a bronsted-Lowry base ?

Answer 2

A species that accepts a proton

Question 3

Just to be aware

Answer 3

Question 4

What happens when you react a base with water ?

Answer 4

You form an OH^- ion

Question 5

What are monoprotic acids and what are monobasic acids ?

Answer 5

• monoprotic - Acids that donates one H⁺ ion per molecule
  Example : HNO₃
• monobasic acids react with only one mole of base per mole of acid in neutralisation (for each mole of acid in neutralisation)

Question 6

What are diprotic acids and what are dibasic acids ?

Answer 6

• Diprotic : Acids that donates **two H⁺ per molecule.
  Example: H₂SO₄
• Dibasic : Acid that reacts with two moles of a base per mole of acid.

Question 7

What are triprotic acids and what are tribasic acids ?

Answer 7

• Triprotic : Acids that donate three H⁺ per molecule.
  Example : H₃PO₄
• Tribasic : Acids that react with three moles of a base per mole of acid.

Question 8

What is a conjugate acid ?

Answer 8

The species that has GAINED a proton.
(Opposite of brownsted-Lowry and standard acids)

Question 9

What is a conjugate base

Answer 9

The species that has LOST a proton.

(Opposite of brownsted-Lowry and standard base )

Question 10

Example of weak base and what type of reaction is favoured.

Answer 10

Question 11

Example of weak acid and what type of reaction is favoured

Answer 11

Question 12

Example of strong acid and what type of reaction is favoured

Answer 12

Equilibrium lies well over to the right

Question 13

Example of strong base and what type of reaction is favoured

Answer 13

Equilibrium lies well over to the left

Question 14

How can we calculate pH when we are given the concentration of H⁺

Answer 14

Question 15

What is the ionic product of water

Answer 15

In water , the water dissociates into its ions very weakly is [H2O] is very much greater than [H+] and [OH-] that [H2O] is effectively a constant number. We assume that the concentration of water has a constant value.

Question 16

What is the units and formula of Kw ?

Answer 16

Mol² dm^-6

Question 17

What is the value of Kw and pH (unless sated otherwise)

Answer 17

10^-14 and 7

Question 18

What is the equation for Kw in pure water

Answer 18

As we can assume that the amount of H+ ions is the same as the amount of OH- ions

Question 19

What is the effect of temperature on Kw ?

Answer 19

Peep how its and endothermic reaction (on false card 14) so if temp increases Kw increase and therefore pH decrease

Question 20

How do we calculate pH of pure water

Answer 20

Question 21

Tip when calculating the pH of diprotic acids (Strong acids)

Answer 21

x2 of the concentration

Question 22

When we are calculating the pH of strong acids what should we assume in terms of concentration ?

Answer 22

We assume that the Strong acids dissociate fully.
- Therefore the concentration of the acids=concentration of H⁺

Question 23

When we are calculating the pH of strong bases what should we assume in terms of concentration ?

Answer 23

We assume that the Strong bases dissociate fully.
- Therefore the concentration of the base=concentration of OH^-

Question 24

How do we calcite the pH of a base ?

Answer 24

Rearrange the Kw expression to get H+
And then pH = -log[H+]

Question 25

When calculating the [H+] after being given the pH of a **diprotic acid ** what should we always remember to do ?

Answer 25

➗ by 2 to get 1 H+ concentration

Question 26

Answer 26

We are only x2 because it’s a diprotic acid

Question 28

The bigger the value of Ka what happens to the strength of it ?

Answer 28

The bigger the value of Ka, **the stronger the weak acid**

Question 29

The smaller the value of pKa what happens to the strength of the acid ?

Answer 29

The smaller the value of pKa, **the stronger the weak acid**

Question 30

For weak acids and bases what **can’t we assume** that we can for strong acids and bases ?

Answer 30

That the concentration of the acid or base is = to the concentration of H+ or OH- ions. - With weak acids and bases we can’t assume this because they don’t fully dissociate.

Question 31

How do we calculate Ka ?

Answer 31

R

Question 32

What assume can we make for the dissociation of weak acids ?

Answer 32

Question 33

How do we measure pH experimentally ?

Answer 33

Question 34

How do we carry out a titration ?

Answer 34

Question 35

What type of acids are inficators considered to be ?

Answer 35

Weak acids. on

Question 36

What two forms does an indicator exist in ?

Answer 36

Acid and conjugate base form. In each form it will have two different colours

Question 37

What is the end point of a titration and when is it reached ?

Answer 37

The pH at which the indicator changes color.

Question 38

How should we choose an indicator

Answer 38

To choose the correct indicator, the indicator should change colour very close to the equivalence point so that the visual change signals that the titration is complete (the point where the amount of acid and base are exactly equal). Allergy Chen says : a suitable Indicator must change colour entirely within the vertical part of the titration curve for it to be effective at determining the end point

Question 39

What is the equivalence point ?

Answer 39

The pH at which all of the acid has reacted with the base (or vice versa).

Question 40

What is the pH range for the two suitable indicators ?

Answer 40

Question 41

How would a strong acids strong base titration look like(if OH is added) and give suitable indicators and the pH range

Answer 41

Methyl orange and phenolphalein. - Equivalence point : 7 - If more base is added after the equivalence point, the pH will rise above 7 due to excess OH-. If more acid is added, the pH will drop below 7 due to excess H+.

Question 42

How would a strong acids weak base titration look like and give suitable indicators and the pH range

Answer 42

Methyl orange - Equivalence point : below 7 - excess acid so final ph <7

Question 43

How would a weak acids strong base titration look like and give suitable indicators and the pH range

Answer 43

Phenolphyhalein - Equivalece point : Above 7 - Excess base so final pH >7

Question 44

How would a weak acids weak base titration look like and give suitable indicators and the pH range

Answer 44

No suitable indicator. As there is **no sharp vertical change ** Must use a pH meter

Question 45

How do we find the equivalence point on a graph

Answer 45

At this point we assume that the concentration of H+ ions is the same as the concentration of OH- ions : [H+] = [OH-]

Question 46

Fill out

Answer 46

Question 47

How do we create an acidic buffer solution ?

Answer 47

Concentrations of acid base and salt must be much greater that the concentration of H+

Question 48

What is a buffer solution

Answer 48

Spec : **A system that minimises pH changes on addition of small amount of an acid or a base**. Allery chem : Buffers resit the change in pH in order to keep the solution below pH 7

Question 49

How can we calculate acid buffer solutions ?

Answer 49

You must know the **Ka value** and [of weak acid - HA] and [of salt - A-] - At equilibrium !!!

Question 50

What happens when you add H+, OH- and water to an acidic buffer solution

Answer 50

Tbh just keep watching this skip to 1:00:00 [Link](https://youtu.be/6xHwx6Y1TgA?si=4RMUuRraRgauAomV)

Question 51

What expressions can we Use in buffers ?

Answer 51

Question 52

What do you understand about buffers in our blood ?

Answer 52

Question 53

Tricky part of buffer

Answer 53

Adding H+ will react with all the salt to form weak acid. HA will increase by the number of moles of H+ added A- will decreases as it’s used up by the same number it moles of H+ added

Question 54

How do we create a basic buffer

Answer 54

Concentrations of weak base and salt must be much greater that the concentration of H+

Question 55

What happens when we add H+, OH- and water to a basic buffer