Module 2: ACIDITY AND BASICITY OF ORGANIC COMPOUNDS

Question 1

• acids and bases are defined through three main concepts:

Answer 1

✓ Arrhenius Theory
✓ Brønsted-Lowry Theory
✓ Lewis electron pair Theory

Question 2

BRønsted-Lowry Theory

• a “base” is any species that can _________________
• a Brønsted-Lowry base must have at least one lone pair of electron to be able to form bond with a proton

Answer 2

accept a proton

Question 2

gives the exact strength of a given acid in water

Answer 2

Ka (acidity constant)

Question 3

ArrHenius Theory

• “acid” is any species that can increase the concentration of ______________ in an aqueous solution

Answer 3

hydrogen ions (protons)

HCl → H+ + Cl–

Question 3

ArrHenius Theory

• “base” is any species that can increase the concentration of _____________ in an aqueous solution

Answer 3

hydroxide ions, OH–,

NaOH → Na+ + OH–

Question 4

BRønsted-Lowry Theory

• an “acid” is any species that can _________________________
• a Brønsted-Lowry acid must have a hydrogen that can dissociate as H+

Answer 4

donate a proton (H+)

Question 4

___________ react almost completely with water

Answer 4

stronger acids (eg. inorganic acids)

Question 5

Lewis “electron” pair Theory

• an “acid” is a species that can _______________

Answer 5

accept a pair of non-bonding electrons

Question 5

in a Brønsted-Lowry acid-base reaction

a _______________ is the species formed after an acid donates its proton

Answer 5

conjugate base

Question 5

HCl (aq) + H2O (l) → H3O+(aq) + Cl–(aq)

__________ acts as the Brønsted-Lowry acid; __________ is the conjugate base of HCl

Answer 5

1. HCl
2. Cl

Question 5

react only slightly with water

Answer 5

weak acids (eg. acetic acid)

Question 5

HCl (aq) + H2O (l) → H3O+(aq) + Cl–(aq)

__________ is the Brønsted-Lowry base; ________
is the conjugate acid of the water

Answer 5

1. H2O
2. H3O+

Question 5

in a Brønsted-Lowry acid-base reaction

____________ is a species formed after the base accepts a proton

Answer 5

conjugate acid

Question 5

acid strengths are normally given using

Answer 5

pKa values (pKa = –log Ka)

Question 6

• note that the negative logarithm in the definition of pKa indicates an _____________ between Ka and pKa

Answer 6

inverse relationship

Question 6

Lewis electron pair Theory

• suggest that acids react with bases, ___________, with no change in the oxidation numbers of any atoms

Answer 6

sharing a pair of electrons

Question 6

Lewis electron pair Theory

• a “base” is a species that can ________________

Answer 6

donate a pair of non-bonding electrons

Question 6

pOH

Answer 6

power of hydroxide

Question 7

• the Lewis structure of “water” shows that it has a _________________________, therefore acting as the Lewis base

Answer 7

non-bonding pairs of valence electrons

Question 8

• the reaction between a Lewis acid and a Lewis base gives rise to an _______________

Answer 8

acid-base complex or complex ion

Question 8

• the “aluminum ion” (Al3+) suggests that it has free orbitals that can ________________________ donated by the water molecules, thereby acting as the Lewis acid

Answer 8

accept pairs of non-bonding electrons

Question 9

pH means

Answer 9

power of hydrogen

Question 10

• the acidity and basicity of a substance can be measured in terms of the molar ___________________________ ions, respectively

Answer 10

concentration of the hydrogen (H+) or hydroxide (OH–)

Question 10

• pOH is defined as the _________________ ion concentration of a substance

Answer 10

negative logarithm of the OH–

Question 10

* pH is defined as the _________________ ion concentration of a substance

Answer 10

negative logarithm of the H+

Question 11

pH of battery acid

Answer 11

0 pH

Question 12

pH of stomach acid

Answer 12

1 pH

Question 13

pH of vinegar

Answer 13

2 pH

Question 14

pH of tomato

Answer 14

4 pH

Question 14

pH of baking soda

Answer 14

9 pH

Question 15

pH of orange juice

Answer 15

3 pH

Question 15

pH of sea water

Answer 15

8 pH

Question 15

pH of black coffee

Answer 15

5 pH

Question 16

pH of urine

Answer 16

6 pH

Question 16

pH of indigestion tablet

Answer 16

10 pH

Question 16

pH of water

Answer 16

7 pH

Question 17

8 - 14 pH

Answer 17

Base (alkali)

Question 17

pH of ammonia solution

Answer 17

11 pH

Question 17

neutral pH

Answer 17

7

Question 17

pH of bleach

Answer 17

13 pH

Question 18

0 - 6 pH

Answer 18

Acid

Question 18

pH of soapy water

Answer 18

12 pH

Question 19

pH of drain cleaner

Answer 19

14 pH

Question 20

* the pH of a solution may be measured using _____________

Answer 20

pH paper

Question 20

* pH paper measures the pH of the solution by __________________ depending on the concentration of H+ and OH–ions

Answer 20

changing its color

Question 21

* this paper is treated with an indicator, which is ______________, an "anthocyanin" commonly found in "red cabbages"

Answer 21

flavin

Question 22

* this paper is treated with an indicator, which is flavin, an ___________ commonly found in red __________________

Answer 22

1. anthocyanin 2. red cabbages

Question 23

* flavin usually turns: * ___________ if the solution is acidic * ___________ if the solution is neutral * ___________ if the solution is basic

Answer 23

1. red 2. greenish 3. purple

Question 24

* ________________ is a more accurate method than pH paper

Answer 24

pH meter

Question 25

* contains a _____________that passes the electrical signals to the meter itself which interprets the electrical signals and display the results on its screen

Answer 25

probe

Question 26

* the glass pH probe contains two electrodes: ____________ that contains a pH 7 buffer solution

Answer 26

sensor electrode

Question 27

* the glass pH probe contains two electrodes: _______________ that usually contains saturated potassium chloride solution

Answer 27

reference electrode

Question 28

* these electrodes made up of porous glass have both a silver wire covered with ________________

Answer 28

silver chloride or calomel

Question 29

* when the probe is immersed in a solution, the ____________ accumulate around the bulb of the electrode, generating an electrical flow captured by the silver wire

Answer 29

hydrogen ions

Question 30

* the _____________ is measured by the meter and then converts it to pH value

Answer 30

voltage of this electrical flow

Question 31

CLASSIFICATION OF pH = 0.1 M acetic acid

Answer 31

acidic (weak)

Question 32

CLASSIFICATION OF pH = 0.1 M acetamide

Answer 32

basic (weak)

Question 33

CLASSIFICATION OF pH = 0.1 M phenol

Answer 33

acidic (weak)

Question 34

CLASSIFICATION OF pH = aniline

Answer 34

basic (weak)

Question 34

CLASSIFICATION OF pH = 0.1 M glycine

Answer 34

neutral (theoretically)

Question 35

CLASSIFICATION OF pH = 1% glucose

Answer 35

neutral (theoretically)

Question 36

CLASSIFICATION OF pH = acetone

Answer 36

acidic to neutral

Question 37

CLASSIFICATION OF pH = isopropyl alcohol

Answer 37

acidic (weak)

Question 38

pH scale allows us to easily classify substances based on their acidity and basicity at ____________

Answer 38

25°C

Question 39

indicator of pH paper

Answer 39

flavin