Unit 4 Toxins, Section IV, L17-22
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Unit 4 Toxins, Section IV, L17-22
Transcript of Unit 4 Toxins, Section IV, L17-22
Unit 4 Toxins, Section IV, L17-22
Lesson 17 Heartburn
Lesson 18 Pass the Proton
Lesson 19 pHooey!
Lesson 20 Watered Down
Lesson 21 Neutral Territory
Lesson 22 Drip Drop
Acids and Bases
What are the properties of acids and bases?
› identify acids and bases based on general
observable properties
› explain how an indicator is used to determine whether a solution is acidic, basic, or neutral
Indicator: An indicator is a molecular substance that changes color when it comes into contact with an acid or a base.
Almonds contain Amygdalin
which, under certain conditions
can produce hydrogen cyanide.
In fact, cyanide gas has an
almond scent.
Produce H+ (as H3O+) ions in water (the hydronium ion is a
hydrogen ion attached to a water molecule)
Taste sour
Corrode metals (react to form H2(g))
Electrolytes
React with bases to form a salt and water
pH is less than 7
Turns blue litmus paper to red
Produce OH- ions in water
Taste bitter, chalky
Are electrolytes
Feel slippery
React with acids to form salts and water (neutralize)
pH greater than 7
Turns red litmus paper to blue “Basic Blue”
NaOH sodium hydroxide lye
KOH potassium hydroxide liquid soap
Mg(OH)2 magnesium hydroxide Milk of magnesia
Al(OH)3 aluminum hydroxide Maalox (antacid)
hydro- prefix
-ic ending
2 elements
-ate ending
becomes
-ic ending
-ite ending
becomes
-ous ending
no hydro- prefix
3 elements
ACIDSstart with 'H'
HBr hydrobromic acid
carbonic acid
sulfurous acid
H2CO3
H2SO3
An easy way to remember…
“In the cafeteria, you ATE something ICky”
Hydrogen bromide
Hydrogen carbonate
Hydrogen sulfite
The substances on the left side of the number line (from 0 to 7) are all acids.
The substances on the right side of the number line (from 7 to 14) are called bases.
The substances located in the middle of the number line (around 7) are called neutral substances.
What are the properties of acids and bases?
› Acids and bases are solutions that are
classified according to their observable
behavior.
› Acids and bases change the color of
indicators.
› Substances that are not acids or bases are
considered neutral.
Acid-Base Theories
How are acids and bases defined?
› define Arrhenius and Brønsted-Lowry acids
and bases
› explain the behavior of acids and bases on
a particulate level
› explain the difference between strong and
weak acids and bases
Acids are substances that add H+ to solution.
Bases are substances that add OH- to solution.
Svante Arrhenius made the revolutionary
suggestion that some solutions contain ions &
that acids produce H3O+ (hydronium) ions in
solution.
+ Cl H
H
H
O
+ H
H
H O Cl +
Arrhenius (traditional)
Acids – increase [H+] in aqueous solutions
(H3O+)
Bases – produce OH- ions in solution OR react with water to remove a H leaving OH-
Arrhenius acid is a substance that produces H+ (H3O+) in water
Arrhenius base is a substance that produces OH- in water
Acid – a molecule or ion that is a proton donor
Bases – a molecule or ion that is a proton acceptor
After all, a “proton” is really just a hydrogen atom that has lost it’s electron!
A Brønsted-Lowry acid is a proton donor
A Brønsted-Lowry base is a proton acceptor
acid base
The Brønsted-Lowry definition also means NH3 is a BASE in water — and water is itself acts as an
!
Lewis acid - a substance that accepts an electron pair
Lewis base - a substance that donates an electron pair
G.N. Lewis H+
H-N-H
H
..
H
H:N-H
H
Formation of hydronium ion is also an
excellent example.
Electron pair of the new O-H bond originates on the Lewis base.
HH
H
BASE
••••••
O—HO—H
H+
ACID
Lewis acid - a substance that accepts an electron pair
The heme group in
hemoglobin can
interact with O2
and CO.
The Fe ion in
hemoglobin is a
Lewis acid
O2 and CO can act
as Lewis bases
• When an acid gives up a proton, it can re-accept that proton (act as a base) and visa versa
• “Conjugate” acids and bases are found on the products side of the equation.
+ Cl H H
H
O
+ H
H
H O Cl +
acid base conjugate acid conjugate base
conjugate acid-base pairs
Label the acid, base, conjugate acid, and
conjugate base in each reaction:
HCl + OH- Cl- + H2O
H2O + H2SO4 HSO4- + H3O
+
acid base conjugate base conjugate acid
acid base conjugate base conjugate acid
Acids and bases that break apart (dissociate) completely in solution are called strong acids and strong bases.
Acids and bases that do not dissociate completely in solution are called weak acids and weak bases.
HNO3, HCl, H2SO4 and HClO4 are among the
only known strong acids.
Strong and Weak Acids/Bases
The strength of an acid (or base) is
determined by the amount of IONIZATION.
Weak acids are much less than 100%
ionized in water.
One of the best known is acetic acid =
CH3CO2H
Strong Base: 100% dissociated in
water.
NaOH (aq) ---> Na+ (aq) + OH- (aq)
Strong and Weak Acids/Bases
Other common strong bases
include KOH and Ca(OH)2.
CaO (lime) + H2O -->
Ca(OH)2 (slaked lime)
CaO
Weak base: less than 100% ionized in
water
One of the best known weak bases is ammonia
NH3 (aq) + H2O (l) NH4+ (aq) + OH- (aq)
Strong and Weak Acids/Bases
[H+] and pH
How is pH related to the acid or base concentration of a solution?
› explain the mathematical relationship
between the H+ and OH– concentrations in
a solution
› define pH and explain the relationship
between H+ concentration and pH
› determine the H+ concentration of a
solution given the [OH–], and vice versa
The pH scale is a logarithmic scale that
describes the concentration of H+ ions in
solution.
pH is related to [H+] by the formula
pH = -log [H+]
If the pH of Coke is 3.12, [H+] = ???
Because pH = - log [H+] then
- pH = log [H+]
Take antilog (10x) of both
sides and get
10-pH = [H+] [H+] = 10-3.12 = 7.6 x 10-4 M
*** to find antilog on your calculator, look for “Shift” or “2nd
function” and then the log button
pH = - log [H+] Example: If [H+] = 1 x 10-10
pH = - log (1 x 10-10)
pH = - (- 10)
pH = 10
Example: If [H+] = 6.2 x 10-9
pH = - log (6.2 X 10-9)
pH = - (- 8.21)
pH = 8.21
• from French – pouvoir hydrogene meaning hydrogen power
Def ined as: the negat ive of the common logar i thm* of the hydronium ion concentrat ion
another way to indicate [H3O+]
* Common log is the power to which 10 must be raised to equal the number
[H+] is critical in many chemical reactions.
A quick method of denoting [H+] is via pH.
By definition pH = – log [H3O+], [H+] = 10-pH
The pH scale describes a wide range of values
The pH scale condenses possible values of [H+]
to a 14 point scale
Also, it is easier to say pH = 7 vs. [H+] = 1 x 10–7
The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the negative power of 10 on the Molarity of the H+ (or OH-) ion.
There are several ways to test pH
Blue litmus paper (red = acid)
Red litmus paper (blue = basic)
pH paper (multi-colored)
pH meter (7 is neutral, <7 acid, >7 base)
Universal indicator (multi-colored)
Indicators like
phenolphthalein
Natural indicators like
red cabbage, radishes
Paper tests like litmus paper
and pH paper Place a drop of the solution onto a
piece of the paper
Read and record the color
change. Note what the color
indicates.
You should only use a small portion
of the paper. You can use one
piece of paper for several tests.
Tests the voltage of the
electrolyte
Converts the voltage
to pH
Very cheap, accurate
Must be calibrated
with a buffer solution
Indicators are dyes that can be added that will
change color in the presence of an acid or
base.
Some indicators only work in a specific range
of pH
Some dyes are natural,
like radish skin or
red cabbage
As acids get stronger, [H+] , pH . A pH of 1 is a very strong acid.
As bases get stronger, [H+] , pH . A pH of 14 is a very strong base.
NOTE: this is an inverse relationship:
pH [H+] [OH-] pOH
Pure water has an [H+]
concentration of 1.0 x 10–7 M and an
[OH–] of 1.0 X 10–7 M.
What does this mean?
Remember: H2O can function as both an
ACID and a BASE.
In pure water there can be
AUTOIONIZATION
Let’s start with water
Water undergoes slight self-ionization:
in H2O @ 25°C: [H3O+] = 1.0 X 10-7 M
[OH-] = 1.0 X 10-7 M
because [OH-] = [H3O+] it is considered neutral
SO…if [OH-] < [H3O+] you have an acid
[OH-] > [H3O+] you have a base
for water [OH-][H3O+] = 1.0 X 10-14
This is known as the ionization constant
(Kw) and can be used in calculations to find
[OH-] and/or [H3O+] for any acid or base
solution with a known molarity.
one more thing to know before calculating begins…
Strong acids and bases are considered completely ionized or dissociated in water.
For example 2 X 10-4 M HCl has 2 X 10-4 M [H3O+]
It has been determined that 1 mole of acid (or base) = 1 mole of H3O
+ (or OH-). In other words: .01 M NaOH has 1.0 X 10-2 moles [OH-]
So, if 2 X 10-4 M HCl has a 2 X 10-4 M
[H3O+], what is the [OH-]?
hint: remember that Kw = [OH-][H3O+] = 1.0 X 10-14
hint: use your Algebra skills to solve for the unknown
Luke, use the force…
[OH-] = 1.0 X 10-14
[H3O+]
= 1.0 X 10-14 = 5.0 X 10-10
2.0 X 10-4
2.0 X 10-4 > 5.0 X 10-10 acid
H+ concentration OH– concentration pH
1.0 X 100 M 1.0 X 10–14 M 0
1.0 X 10–1 M 1.0 X 10–13 M 1
1.0 X 10–2 M 1.0 X 10–12 M 2
1.0 X 10–3 M 1.0 X 10–11 M 3
1.0 X 10–4 M 1.0 X 10–10 M 4
1.0 X 10–5 M 1.0 X 10–9 M 5
1.0 X 10–6 M 1.0 X 10–8 M 6
1.0 X 10–7 M 1.0 X 10–7 M 7
1.0 X 10–8 M 1.0 X 10–6 M 8
1.0 X 10–9 M 1.0 X 10–5 M 9
1.0 X 10–14 M 1.0 X 10–0 M 14
More
acidic
More basic
neutral
What is the pH of a 0.0010 M NaOH solution?
[OH-] = 0.0010 (or 1.0 X 10-3 M)
pOH = - log 0.0010
pOH = 3
pH = 14 – 3 = 11
OR Kw = [H3O+] [OH-]
[H3O+] = 1.0 x 10-11 M
pH = - log (1.0 x 10-11) = 11.00
Youtube review
A solution has a pH of 8.5. What is the
Molarity of hydrogen ions in the solution?
pH = - log [H+]
8.5 = - log [H+]
-8.5 = log [H+]
Antilog -8.5 = antilog (log [H+])
10-8.5 = [H+]
3.16 X 10-9 = [H+]
What is the [H+] if pH = 7.4?
[H+] = 10–pH mol/L
3.98 x 10–8 M
pH = -log[H+] -pH = log [H+] Antilog (-pH) = [H+] 1 x 10-pH = [H+]
Both humans and aquatic organisms depend on water.
The pH of water must be within a range of 5 to 9 in order for organisms to survive.
Waters with a pH less than about 5 are too acidic for humans to drink and will not allow most aquatic life to survive.
Waters that are too basic can also harm humans, plants, and animals. Water with a pH of greater that 9 can dissolve materials such as animal scales and skin.
Hank on pH
It’s very important that the pH
levels of water don’t increase or decrease
too much out of a certain range.
This change could affect food chains and the survival of species.
How can pH levels change?
pH can be affected by the chemicals in the water.
The pH of water affects organisms living in the water. A changing pH in water can mean that there is an increase of pollution or some other environmental factor.
Things such as burning fossil fuels (like with cars), mining, chemical spills, runoff (washing cars and farming), and sewage cause pH levels to change.
How is pH related to the acid or base concentration of a solution? › The pH scale is a logarithmic scale that describes
the concentration of hydrogen ions, H+, in solution: pH = -log [H+].
› The H+ concentration is related to the OH–
concentration: [H+][OH–] =10–14. So, as [H+] increases, [OH–] decreases, and vice-versa.
› The pH of water is 7. In water the H+ concentration is equal to the OH– concentration. Thus, water is neutral.
Acid/Base Reactions
Acidic compounds react with basic compounds and neutralize each other producing a salt (and usually gas and water too!)
NaHCO3 + HCl NaCl + H2(g) + H2O
Base Acid Salt
Neutralization is the reaction of hydronium ions and hydroxide ions to form water.
?! Huh?!
What happens when HCl and NaOH are combined in water?
NaOH + H2O dissociates to produce Na+ and OH- ions
HCl completely ionizes in H2O to produce H3O+ and Cl- ions
The equation of the reaction:
H3O+ + Cl- + Na+ + OH- Na+ + Cl- + 2H2O
Cl– and Na+ appear on both sides of the equation and are known as “spectator ions”
If the solution evaporates, and additional product is formed: NaCl – a salt: an ionic compound formed of a cation from a base and an anion from an acid.
We can use this knowledge to find an
unknown concentration of an acid or a base
by performing a procedure known as a
titration
1. Add solution from the buret.
2. Reagent (base) reacts with compound (acid) in solution in the flask.
3. Indicator shows when exact stoichiometric reaction has occurred. (Acid = Base)
This is called
NEUTRALIZATION.
A neutralization reaction
Dilution
Add water to the 3.0 M solution to lower
its concentration to 0.50 M
Dilute the solution!
But how much water
do we add?
How does dilution affect acids and bases?
How much water is added?
The important point is that --->
moles of NaOH in ORIGINAL solution =
moles of NaOH in FINAL solution
Amount of NaOH in original solution =
M • V =
(3.0 mol/L)(0.050 L) = 0.15 mol NaOH
Amount of NaOH in final solution must also =
0.15 mol NaOH
Volume of final solution =
(0.15 mol NaOH)(1 L/0.50 mol) = 0.30 L
or 300 mL
Conclusion:
add 250 mL of
water to 50.0
mL of 3.0 M
NaOH to make
300 mL of 0.50
M NaOH.
A shortcut
M1 • V1 = M2 • V2
You have a stock bottle of hydrochloric
acid, which is 12.1 M. You need 400 mL
of 0.10 M HCl. How much of the acid
and how much water will you need?
M1V1=M2V2
12.1(x) = (400)(0.10)
12.1x = 40
x = 3.3
• complete a serial dilution of a solution
• explain the effect of dilution on the acidity or basicity of a solution
Adding water to an acid or a base dilutes the solution, making it less acidic or less basic.
NOTE! An acid can never be turned into a base by diluting it with water, and a base can never be turned into an acid by diluting it with water.
Each time the H+ concentration is diluted tenfold, the pH number goes up 1 unit.
pH H+ concentration (decimal
number)
H+ concentration
(scientific notation)
2 0.010 mol/L 1.0 X 10–2 mol/L
3 0.0010 mol/L 1.0 X 10–3 mol/L
4 0.00010 mol/L 1.0 X 10–4 mol/L
5 0.000010 mol/L 1.0 X 10–5 mol/L
6 0.0000010 mol/L 1.0 X 10–6 mol/L
7 0.00000010 mol/L 1.0 X 10–7 mol/L
Neutralization Reactions
Excess stomach acid, HCl, can
cause extreme discomfort and
pain. Milk of magnesia, Mg(OH)2,
is often taken to reduce stomach
acid.
a. What products do you think are
produced when Mg(OH)2 and HCl
are mixed?
b. What products do you think are
produced when HNO3 and HCl are
mixed?
What happens when acids and bases are mixed?
• write a chemical equation for an acid-base
neutralization reaction
• describe how the pH changes when acids and bases are mixed
A neutralization reaction between a strong acid
and a strong base in aqueous solution produces an
ionic compound (salt) and water.
A neutralization reaction can be
described as a double exchange
reaction in which the two compounds
exchange cations.
Sulfuric acid, H2SO4(aq), reacts with
magnesium hydroxide, Mg(OH)2(aq). Write
a balanced equation for the reaction that
occurs.
H2SO4(aq) + Mg(OH)2(aq) MgSO4 + H2O
