Module 2: ACIDITY AND BASICITY OF ORGANIC COMPOUNDS Flashcards
- acids and bases are defined through three main concepts:
✓ Arrhenius Theory
✓ Brønsted-Lowry Theory
✓ Lewis electron pair Theory
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
accept a proton
gives the exact strength of a given acid in water
Ka (acidity constant)
ArrHenius Theory
- “acid” is any species that can increase the concentration of ______________ in an aqueous solution
hydrogen ions (protons)
HCl → H+ + Cl–
ArrHenius Theory
- “base” is any species that can increase the concentration of _____________ in an aqueous solution
hydroxide ions, OH–,
NaOH → Na+ + OH–
BRønsted-Lowry Theory
- an “acid” is any species that can _________________________
- a Brønsted-Lowry acid must have a hydrogen that can dissociate as H+
donate a proton (H+)
___________ react almost completely with water
stronger acids (eg. inorganic acids)
Lewis “electron” pair Theory
- an “acid” is a species that can _______________
accept a pair of non-bonding electrons
in a Brønsted-Lowry acid-base reaction
a _______________ is the species formed after an acid donates its proton
conjugate base
HCl (aq) + H2O (l) → H3O+(aq) + Cl–(aq)
__________ acts as the Brønsted-Lowry acid; __________ is the conjugate base of HCl
- HCl
- Cl
react only slightly with water
weak acids (eg. acetic acid)
HCl (aq) + H2O (l) → H3O+(aq) + Cl–(aq)
__________ is the Brønsted-Lowry base; ________
is the conjugate acid of the water
- H2O
- H3O+
in a Brønsted-Lowry acid-base reaction
____________ is a species formed after the base accepts a proton
conjugate acid
acid strengths are normally given using
pKa values (pKa = –log Ka)
- note that the negative logarithm in the definition of pKa indicates an _____________ between Ka and pKa
inverse relationship
Lewis electron pair Theory
- suggest that acids react with bases, ___________, with no change in the oxidation numbers of any atoms
sharing a pair of electrons
Lewis electron pair Theory
- a “base” is a species that can ________________
donate a pair of non-bonding electrons
pOH
power of hydroxide
- the Lewis structure of “water” shows that it has a _________________________, therefore acting as the Lewis base
non-bonding pairs of valence electrons
- the reaction between a Lewis acid and a Lewis base gives rise to an _______________
acid-base complex or complex ion
- the “aluminum ion” (Al3+) suggests that it has free orbitals that can ________________________ donated by the water molecules, thereby acting as the Lewis acid
accept pairs of non-bonding electrons
pH means
power of hydrogen
- the acidity and basicity of a substance can be measured in terms of the molar ___________________________ ions, respectively
concentration of the hydrogen (H+) or hydroxide (OH–)
- pOH is defined as the _________________ ion concentration of a substance
negative logarithm of the OH–
- pH is defined as the _________________ ion concentration of a substance
negative logarithm of the H+
pH of battery acid
0 pH
pH of stomach acid
1 pH
pH of vinegar
2 pH
pH of tomato
4 pH
pH of baking soda
9 pH
pH of orange juice
3 pH
pH of sea water
8 pH
pH of black coffee
5 pH
pH of urine
6 pH
pH of indigestion tablet
10 pH
pH of water
7 pH
8 - 14 pH
Base (alkali)
pH of ammonia solution
11 pH
neutral pH
7
pH of bleach
13 pH
0 - 6 pH
Acid
pH of soapy water
12 pH
pH of drain cleaner
14 pH
- the pH of a solution may be measured using _____________
pH paper
- pH paper measures the pH of the solution by __________________ depending on the concentration of H+ and OH–ions
changing its color
- this paper is treated with an indicator, which is ______________, an “anthocyanin” commonly found in “red cabbages”
flavin
- this paper is treated with an indicator, which is flavin, an ___________ commonly found in red __________________
- anthocyanin
- red cabbages
- flavin usually turns:
- ___________ if the solution is acidic
- ___________ if the solution is neutral
- ___________ if the solution is basic
- red
- greenish
- purple
- ________________ is a more accurate method than pH paper
pH meter
- contains a _____________that passes the electrical signals to the meter itself which interprets the electrical signals and display the results on its screen
probe
- the glass pH probe contains two electrodes:
____________ that contains a pH 7 buffer
solution
sensor electrode
- the glass pH probe contains two electrodes:
_______________ that usually contains saturated potassium chloride solution
reference electrode
- these electrodes made up of porous glass have both a silver wire covered with ________________
silver chloride or calomel
- 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
hydrogen ions
- the _____________ is measured by the meter and then converts it to pH value
voltage of this electrical flow
CLASSIFICATION OF pH
= 0.1 M acetic acid
acidic (weak)
CLASSIFICATION OF pH
= 0.1 M acetamide
basic (weak)
CLASSIFICATION OF pH
= 0.1 M phenol
acidic (weak)
CLASSIFICATION OF pH
= aniline
basic (weak)
CLASSIFICATION OF pH
= 0.1 M glycine
neutral (theoretically)
CLASSIFICATION OF pH
= 1% glucose
neutral (theoretically)
CLASSIFICATION OF pH
= acetone
acidic to neutral
CLASSIFICATION OF pH
= isopropyl alcohol
acidic (weak)
pH scale allows us to easily classify substances based on their acidity and basicity at ____________
25°C
indicator of pH paper
flavin
