Transcript Acids and Bases - Ms. Drury's Flipped Chemistry Classes

Acids and Bases
A substance that dissolves in water and conduct
electricity. Acids and bases are electrolytes.
◦ Acid: Substance that, when
dissolved in water, increases the
concentration of hydrogen H+
(or hydronium H3O+) ions.
◦ Acids have a sour taste and can burn
your skin.
◦ Acids react vigorously with metals to
make H2
◦ pH is less than 7
◦ On table K
Base: Substance that, when dissolved
in water, increases the concentration
of hydroxide ions.
 Bases have a bitter taste and are
corrosive.
 pH>7
 On Table L


If an acid is added to a base, it results in
neutralization, where all properties of the
acid and base are lost. The products are a salt
and water.
NaOH + HCl  H2O + NaCl
Salt is another name for solid ionic compounds
containing elements other than H+ and OH-.
Salts are electrolytes with high mp and bp.
1.
H2SO4 + LiOH  H2O + Li2SO4
Acid
2.
Salt
Base
KOH + HNO3  KNO3 + H2O
Base
Acid
Salt
1.
NaOH + HF  H2O + NaF
2.
Ca(OH)2 + H2SO4  H2O + CaSO4
Make sure you check your compounds with the
criss cross rule for ions!
Alternate Acid Base Theory
◦Acid:
◦Base:
Proton donor
Proton acceptor
Protons refer to hydrogen ions.
H
H+
HCO3−
−
HSO4
H2O
These all have hydrogen atoms to
donate and a negative charge
that would attract H+


Water acts as a
Brønsted–Lowry
base and
removes a
proton (H+)
from the acid.
As a result, the
conjugate base
of the acid and
a hydronium
ion are formed.

Reactions between acids and bases always
yield their conjugate bases and acids.
Strong acids and bases are completely
dissociated in water to make a lot of
H+or OH-.
 Weak acids and bases only dissociate
partially in water to make a small
amount of H+or OH-.


How is strength different from
concentration?
Strength refers to the amount of ions
a substance makes when it breaks
down.
 Concentration refers to the amount of
the substance initially, before it
breaks down. This is usually measured
in molarity (mol/L).

pH and indicators

For less accurate
measurements,
one can use
◦ Litmus paper
 “Red” paper
turns blue
above ~pH = 8
 “Blue” paper
turns red below
~pH = 5
◦ An indicator
For more accurate
measurements, one
uses a pH meter,
which measures the
voltage in the
solution.

Hydrangeas are blue when the acidity of
the soil is between 5-5.5 and red if the
acidity is between 6.5-7.5. A mix of colors
can be seen between 5.5-6.5.
If the pH goes up one, the
concentration of hydrogen ions
decreases by 10. The solution is more
basic.
 If the pH goes down one, the
concentration of hydrogen ions
increases by 10. The solution is more
acidic.




If the pH changes from 3 to 4, how much
more basic is the solution?
If the pH = 3 and the hydrogen concentration
increases by 100 times, what is the new pH?
If the pH = 8 and the hydrogen ion
concentration decreases by 10,000 times,
what is the new pH?




If NaOH is tested with methyl orange, what
color will it be? yellow
At what pH will bromocrescol green turn
yellow? 3.8
What type of solution will turn bromothymol
blue, yellow? acidic
At what pH will both bromothymol and
thymol blue be yellow? 7.6-8




Why won’t methyl orange be good at
determining the difference between an acid
and a base? Bases and acids can both be yellow
Which indicator is the best to test the Thymol blue
difference between a strong and weak base?
What color change will be seen if NaOH is
added to HCl with methyl orange? Red to yellow
What color change will be seen if nitric acid is
added to lithium hydroxide using
bromocrescol green? Blue to yellow
Titrations



ACID + BASE  SALT + WATER
Salt is another name for any ionic substance.
They can conduct electricity.
HCl + NaOH  NaCl + H2O
acid
base
salt


Titrations are used to find the concentration
of a solution. Usually the concentration of the
base is unknown, so a known acid is added to
the base until the solution neutralizes.
The endpoint, or the point where the solution
is neutral and the titration is over, is marked
by a faint pink color in the solution (due to
phenolphthalein).

To calculate the molarity of the unknown use
the formula on Table T:
MAVA=MBVB
What is the molarity of NaOH if 100.mL of
3.00M HCl is titrated with 200.mL of NaOH?
1.
MAVA=MBVB
2.
(3.00)(100) = x(200)
x = 1.50M
What is the molarity of 100.0mL HCl if it is
neutralized by 250mL of 2.0M NaOH?
MAVA=MBVB
(x)(100) = (2.0)(250)
x = 5.0M

The titration formula only works if the acid and the
base have equal numbers of H+ and OH-. If not, the
acid side must be multiplied by the number of
hydrogen ions and the base side must be
multiplied by the number of hydroxide ions in the
formulas.
◦ What is the molarity of a solution of Ca(OH)2 if
750mL of it is titrated with 250mL of 3.5M
H3PO4?
3MAVA = 2MBVB
3(3.5)(250) = 2(x)(750)
x = 1.75M
How much
acid is in
each burette?
0.6mL
How much
acid was
released?
15.4mL
15.4-.6 =
14.8mL
released
from the
burette.