section 6.3—acidity, ph how does concentration of acid affect the ph of a sports drink?
TRANSCRIPT
Acids – Arrhenius Definition
Produce Hydronium ion (H3O+1) in water
Hydronium ion is water + a hydrogen cation
H
OH
water
H+1
H
OH
H +1
By this definition, if an acid is to give a H+1 to water, then all acids will have hydrogen as the cation (first element written).
Characteristics of Acids & Bases
BasesAcids
Produce H3O+1 (hydronium ion) in water
Produce OH-1 (hydroxide ion) in water
Tastes sour Tastes Bitter
React with active metals to form hydrogen gas
Feels slippery
Strong versus Weak Acids
+
++
-
-
-
Strong acidMost of the acid molecules
have donated the H+1 to water
How many hydronium ion – anion pairs can you find?
How many intact acid molecules can you find?
3
1
Strong versus Weak Acids
+
-
Weak acidOnly a few of the acid
molecules have donated the H+1 to water
How many hydronium ion – anion pairs can you find?
How many intact acid molecules can you find?
1
3
Concentrated versus Dilute
solute solvent
Lower concentration
Not as many solute (what’s being dissolved) particles
Higher concentration
More solute (what’s being dissolved) particles
Combinations of Concentration & Strength
DiluteConcentrated
A lot of acid added & most
dissociates
Not much acid added, but most of
what’s there dissociates
A lot of acid added, but most stays together
Not much acid added and most of what is there stays
together
Strong
Weak
Acids and Bases as Electrolytes
Acids and bases dissociate into ions in water
Free-floating ions in water conduct electricity
Acids & Bases are electrolytes
Strong acids and bases are strong electrolytesWeak acids and bases are weak electrolytes
Is a scale to measure the acidity of a sample
pH Scale
1 14
Highly acidic Very basic (not acidic)
neutral
7
Chapter 6 will give more detail about how pH is calculated!
pH is a Logarithmic Scale
Logarithm –The number of times a base must be multiplied by itself to reach a given number
yx blog# of multiples
Base
# you’re trying to reach
Calculating pH
pH scale – Logarithmic scale of the acidity of a solution
The pH scale uses base “10”
]log[ 13
OHpH
pHOH 10][ 13
pH has not units
[ ] = concentration in Molarity
The “-” in the pH equation
Concentration of Hydronium ion versus pH
0
0.5
1
0 0.5 1 1.5 2
pH
[H3
O+
]
Because pH is the negative log of concentration of hydronium, as concentration increases, the pH goes down.
The lowest pH is the highest concentration of hydronium
What does a “log” scale really mean?
pH
4
3
2
1
10x more acidic
100x more acidic
1000x more acidic
Leve
l of
acid
ity in
crea
ses
Every change of 1 in pH shows a change of 10x in concentration of hydronium
An example of calculating pH
pH = 0.60
]log[ 13
OHpH
)25.0log( MpH
Example:Find the pH if the concentration of [H3O+1] is 0.25 M
An example of calculating hydronium
H3O+1 = 0.0020 M
pHOH 10][ 13
7.213 10][ OH
Example:Find the [H3O+1] if
the pH is 2.7
Auto-ionization of Water
Water will split into ions 2 H2O H3O+1 + OH-1
Water will do this to make sure that at 25°C the following is true: [H3O+1] × [OH-1] = 1 × 10-14
So if you know the hydronium concentration at 25°C (which can be found from pH), then you can also find the hydroxide concentration
An example of calculating hydroxide
14113 101][][ OHOH
14111 101][]100.2[ OH
Example:Find the [OH-1] if the pH is 10.7
H3O+1 = 2.0 × 10-11 M
pHOH 10][ 13
7.1013 10][ OH
]100.2[
101][
11
141
OH
OH-1 = 0.0005 M
Let’s Practice #1
pH = 4.6
]log[ 13
OHpH
)105.2log( 5MpH
Example:Find the pH if the concentration of
[H3O+1] is 2.5 × 10-5 M
Let’s Practice #2
14113 101][][ OHOH
1414 101][]105.2[ OH
Example:Find the [OH-1] if
the pH is 3.6
H3O+1 = 2.5 × 10-4 M
pHOH 10][ 13
6.313 10][ OH
]105.2[
101][
4
141
OH
OH-1 = 4.0 ×10-11 M