acids burn.. bases burn. vi. strength of acids and bases a. strong acids and bases… 1. completely...
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Acids burn.
Bases burn.
VI. Strength of Acids and BasesA. Strong acids and bases…
1. completely dissociate (come apart) or ionizes 100% of the molecules become ions2. are strong electrolytes and dangerous!
Ex. acids: HCl, HBr, HI, HNO3, H2SO4, HClO4
bases: NaOH and other Group 1 or 2 hydroxides
B. Weak acids and bases… 1. dissociate or ionize very little
maybe only 1% of molecules become ions2. are weak electrolytes
Ex: acids: acetic acid, carbonic, and many others bases: ammonia and many others
STRONG ACIDS
STRONG Bases
C. pH Scale1. In any solution, if you pay attention only to the
concentration of hydronium H3O+ (same as H+ !!!)
and hydroxide OH- ions…
…and use brackets [ ] to mean “the concentration of…”
then..
In an acidic solution: [H+] > [OH-]
In a neutral solution: [H+] = [OH-]
In a basic solution: [H+] < [OH-]
Ex. Is the solution shown at right
acidic, basic or neutral?
H+
OH-
H+
H+
OH-
H+
OH- H+
H+
OH-
OH-
OH-
OH-
2. The pH scale is used to express how acidic or basic a solution is.
a/ The pH scale goes from 0 to 14
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
neu
tralstronger acids
more acidicmore [H+] or [H3O+]
stronger basesmore basicmore [OH-]
b/ pH = 7 means a neutral solution with [H+] = [OH-]
Lower pH (< 7): more acidic with [H+] > [OH-]
Higher pH (> 7): more basic with [OH-] > [H+]
Ex. As acid is added to base, what happens to the..
…the pH?
…the acidity? …the basicity?
…the H3O+ concentration? …the OH- concentration?
Ex. Which pH value is most basic?
11 13 2 7 4
Ex. Which pH value it most acidic?
11 13 2 7 4
Ex. Which pH value has the greatest [H3O+]?
11 13 2 7 4
Ex. Which pH value has the greatest [OH-]?
11 13 2 7 4
Sometimes it is written right to left:
Ex. The list at right
gives the pH’s of some
common solutions.
a/ Write A (acid), B (base) and N (neutral) next to each
b/ Put them in order…
…from strongest acid to strongest base:
…of increasing H+ (or H3O+) concentration.
…of increasing OH- concentration.
bleach: 13
blood: 7.4
coffee: 5
OJ: 3
pure water: 7
3/ pH is logarithmic. This means that…
a change …means a change in pH of: in concentration of:
1 101 or 10x
2 102 or 100x
3 103 or 1000x
etc
Ex. Which has a greater [H+] or [H3O+]:
urine (pH 6) or pure water (pH 7)?
How much greater?
Which has a greater [OH-]?
How much greater?
Ex. Which has a greater [H+]: soapy water (pH 12) orbaking soda (pH 9)?
How much greater?Which has a greater [OH-]?How much greater?
Ex. Which has a greater [OH-]: a can of soda (pH 3) or black coffee (pH 5)?
How much greater?
Which has a greater [H30+]?
How much greater?
Ex. The pH of a solution changes from 4 to 3. Did the [H+] decrease or increase? By what factor?Did the [OH-] dec. or incr.? By what factor?
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