Unit 1.2 Acids and Bases

Question 1

What is a dative or coordinate bond?

Answer 1

A covalent bond in which one of the atoms supplies both of the electrons

Question 2

What is Kw

Answer 2

The dissociation constant of water
= 1.01x10-14 (at 25)

Question 3

What is Arrhenius’s theories for acids and bases?

Answer 3

Acids- substances that produce H+ ions in solution
Bases- substances that produce OH- ions in solution

Question 4

What is Bronsted-Lowry’s theory for acids and bases?

Answer 4

Acids- proton (H+) doners
Bases- Proton (H+) acceptors

Question 5

What is a conjugate base?

Answer 5

The substance left after a acid donates its proton

Question 6

What is a conjugate acid?

Answer 6

The substance that gains the proton

Question 7

How does a stronger or weaker acid effect the conjugate base and acid?

Answer 7

The stronger the acid the weaker the conjugate base
The stronger the base the weaker the conjugate acid

Question 8

What is an amphoteric substance?

Answer 8

These are substances that can react as an acid or base

Question 9

What is an example of an amphoteric substance?

Answer 9

Water

Question 10

What does pH stand for?

Answer 10

Potential of hydrogen

Question 11

As the [H3O+] increases what happens to the pH?

Answer 11

The pH decreases

Question 12

What is the pOH- of a solution measure?

Answer 12

[OH-]

Question 13

What expression is used to calculate the [H+] when the pH is known?

Answer 13

[H3O+]=-Log10^-pH

Question 14

What is the expression for calculating pOH?

Answer 14

pOH=-log10[OH-]

Question 15

What is the definition for a strong acid?

Answer 15

An acid that completely dissociates into ions in aqueous solution and is therefore in a equilibrium with a high Ka

Question 16

What are examples of strong acids?

Answer 16

-Hydrochloric acid
-Nitric acid
-Sufuric acid

Question 17

What happens when you dilute a strong acid by a factor of 10?

Answer 17

The pH will change by 1 unit

Question 18

What is the definition for a weak acid?

Answer 18

An acid that only partially dissociates in solution and is therefore in equilibrium with a low Ka

Question 19

What are examples for weak acids?

Answer 19

-Carbonic acid
-Sulphurous acid

Question 20

What does Ka mean?

Answer 20

The acid dissociation constant

Question 21

What value is assigned to water in Ka?

Answer 21

1

Question 22

What does a higher Ka mean?

Answer 22

There is a stronger more dissociated acid

Question 23

What does a low and high Ka indicate?

Answer 23

High Ka- a strong acid
Low Ka- a weak acid

Question 24

What is the expression to find the pH for a strong acid?

Answer 24

pH= -log10[H3O+] so
[H3O+]=10^-pH

Question 25

What is the expression to find the pKa for a weak acid?

Answer 25

pKa= -log10Ka so Ka=10^-pKa

Question 26

What is a Polyprotic acid?

Answer 26

Proyprotic acids have more than one ionisable proton. The protons are removed one by one, not all at once

Question 27

Which stage is the easiest when removing protons in polyprotic acid?

Answer 27

The first proton

Question 28

What does it mean if the acid is equimolar?

Answer 28

They contain the same number of moles per litre

Question 29

What does it mean if the acids are monoprotic?

Answer 29

They both release one H+ per molecule

Question 30

How does a pH value work with a base which doesn't have H+ ions?

Answer 30

-Every water based solution sets up an equilibrium -If additional hydroxide ions are present -The [H+] will decrease to below that of water -pH is a measure of the conc of theses [H+] ions

Question 31

What is a weak base?

Answer 31

They only partially dissociated into ions in aqueous solution

Question 32

Examples of weak base?

Answer 32

Ammonia and amines

Question 33

How is a salt produced?

Answer 33

A substance that is produced when H+ ion of an acid is replaced by a positive ion, usually a metal

Question 34

What happens when a strong acid fully neutralises a strong base?

Answer 34

The pH of the salt solution will always be 7 at 25C

Question 35

Do strong bases and strong acids affect the water dissociation?

Answer 35

It does not affect the water dissociation equilibrium so there are equal concentrations of H+ and OH- ions in solution and pH=7

Question 36

Strong acid/strong base salt pH?

Answer 36

=7

Question 37

Strong acid/ weak base salt pH?

Answer 37

<7

Question 38

Weak acid/ Strong base salt pH?

Answer 38

>7

Question 39

Weak acid/ Weak base salt pH?

Answer 39

Approximately 7

Question 40

What is the end point of a reaction?

Answer 40

The point in a titration that is shown by a change in colour

Question 41

What is an equivalence point?

Answer 41

The point in a neuralisation reaction when the moles of base = moles of acid so the solution only contains salt and water (neutral)

Question 42

What do indicators change colour in response too?

Answer 42

pH

Question 43

What is KIn?

Answer 43

Acid dissociation constant for indicators

Question 44

What pH of an indicator should be chosen for a strong acid / strong base?

Answer 44

One will a pKIn value one less than the pH of the equivalent point , If using a strong base against strong acid it should be one greater than the pH at the equivalent point

Question 45

What pH of an indicator should be used for a weak acid / strong base?

Answer 45

pH ~ 7.5

Question 46

What is a buffer solution?

Answer 46

A solution in which the pH remains approximately constant when small volumes of acid, base or water are added

Question 47

What is an acid buffer made from?

Answer 47

A weak acid and one of its salts from a strong base The salt will supplies the conjugate base of the acid

Question 48

What does the pH of an acid buffer depend on?

Answer 48

The Ka of the weak acid and the ratio of [acid] to [conjugate base] (salt)

Question 49

How can you change the pH of a buffer?

Answer 49

By changing the ratio of acid to salt, or by choosing a different acid and one of its salts

Question 50

How is a basic buffer solution prepared?

Answer 50

A basic buffer consists of a solution of a weak base and one of its salts

Question 51

How does a buffer maintain a constant pH on the addition of acid?

Answer 51

If a small amount of acid is added to the buffer, the weak base removes the excess H+

Question 52

What happens to the pH of a buffer when water is added?

Answer 52

The ration remains unchanged between the base and its salt so the pH stays the same