Download Report

Calendar: Final Exam, Essays & Rockets
Acids & Bases
What are Acids & Bases?
Brønsted–Lowry Acids & Bases
Brønsted–Lowry Acids & Bases
Brønsted–Lowry Acids & Bases
Brønsted–Lowry Acids & Bases
The pH Scale
The pH Scale
The pH Scale
Self-Ionization of Water
The self-ionization of water occurs when two water molecules
spontaneously form one hydronium ion & one hydroxide ion.
A surplus of [H+] means that the solution will be acidic.
A surplus of [OH-] means that the solution will be basic.
Ion Product Constant of Water (Kw)
When the number of H+ ions is equal to the number of OHions, the solution is said to be neutral and it has a pH of 7.0
The [H+] of a neutral solution is 1.0 x 10-7
The Kw is constant and is always equal to 1.0 x 10-14
The Kw equation can be used to solve for [H+] or [OH-]:
Kw = [H+] x [OH-] = 1.0 x 10-14
pH + pOH = 14
Calculating pH
If we know the [H+] for a solution then we can calculate
the pH of that solution using the following formula:
pH = - log [H+]
Calculating pH = -log [H+]
Watch as I calculate pH for the following concentrations:
[H+] = 5.4 x 10-3
[H+] = 3.9 x 10-8
[H+] = 9.8 x 10-5
If the pOH of an unknown solution is 9.5, what is the solution’s pH?
The Strength of Acids & Bases
Part of what determines if an acid or base is "strong" is
the concentration of H+ or OH- ions that it creates when
dissolved in water.
Acids and bases are classified as strong or weak based
on the degree to which they ionize (or disassociate) in
water.
Strong Acid & Weak Acid
Hydrochloric acid is a strong acid because 100% of the
acid molecules disassociate in a water solution:
HCl (g) + H2O(l)  H3O+ + Cl- (100% dissolved)
Formic acid is a weak acid because less than 5% of the
acid molecules disassociate in water:
HCOOH (aq) + H2O(l)  H3O+ + COOH- (5% dissolved)
Types of Chemical Reactions
There are six categories of chemical reaction that
we must know:
1.
2.
3.
4.
5.
6.
Combination reaction
Decomposition reaction
Single-displacement reaction
Double-displacement reaction
Combustion reaction
Acid-Base reaction
Combination & Decomposition
Two or more reactants join together to make products that
are fewer in number but larger in atom count.
A reactant breaks apart to form products that are
greater in number but smaller in atom count.
Single & Double Displacement
An element reacts with a compound to form a new element and a
different compound. The reactant displaces and element in the
compound. For example, a metal will replace a different metal.
Two compounds react to form two new compounds, and the
reacting elements displace each other.
Combustion Reaction
Identifying Chemical Reactions
1. Does the reaction have oxygen as one of its reactants
and carbon dioxide and water as products? If yes,
then it's a combustion reaction.
2. Does the reaction have two (or more) chemicals
combining to form one chemical? If yes, then it's a
combination reaction.
3. Does the reaction have one large molecule falling apart
to make several small ones? If yes, then it's a
decomposition reaction.
Identifying Chemical Reactions
4. Does the reaction have molecules on both sides of the
reaction that contain only one element? If yes, then
it's a single displacement reaction.
5. Does the reaction have water as one of the products? If
yes, then it's an acid-base reaction.
6. If you haven't answered "yes" to any of the questions
above, then the reaction is possibly a double
displacement reaction.
Bonus: Identifying Chemical Rxns
Work alone & work quietly. Notebooks may be open.
Part 1 of 1 is 20 Minutes.
Identify the following reactions as either combustion,
combination, decomposition, single-displacement,
double-displacement or an acid-base reaction.
1. HBr + NaOH  NaBr + H2O
2. 2 H2O  2 H2 + O2
3. C10H8 + 12 O2  10 CO2 + 4 H2O
4. 8 Fe + S8  8 FeS
5. Pb(NO3)2 + 2 KI ---> PbI2 + 2 KNO3
6. Mg + 2 H2O  Mg(OH)2 + H2
Three Types of Chemical Formula
There are three types of chemical formula:
1.
2.
3.
Molecular
Empirical or “Simple”
Structural
An unknown compound has two formulas associated
with it, C8H4O8 and C2HO2, which is the molecular
formula? Which is the empirical formula?
Three Types of Chemical Formula
A molecular formula tells us what atoms are in each
molecule. Empirical formulas give us the ratio of atoms.
Molecular
Empirical
C6H12O6
CH2O
Structural
____________________________________
H2O
H2O
Three Types of Chemical Formula
An unknown compound has two formulas associated with it, C8H4O8
and C2HO2, which is the molecular formula?
Which is the empirical formula?
The molecular formula is C8H4O8 . This formula shows how many of each
atom are present in the molecule.
The empirical formula is C2HO2 . This formula does not show every atom
present in the molecule. There are 4 atoms of hydrogen present that are
not shown. This simplified formula only shows the ratio of the atoms. There
are two carbon for every one hydrogen and every two oxygen.
Reversible Reactions
Reversible Reactions & Equilibrium
Not all reactions are reversible (burning a match is not
reversible).
In a reversible reaction, both the forward and reverse
reactions occur at the same time. At first, the forward
reaction occurs much faster than the reverse reaction.
In time, as the amount of products increases, the reverse
reaction speeds up until both reactions occur at the same
rate. When both reactions occur at the same rate, the
reaction is at equilibrium.
Le Chatelier’s Principle
This principle is named after Henry Louis
Le Chatelier (1850 – 1936) and is often
referred to as the equilibrium law.
When a system at equilibrium is subjected to
change in concentration, temperature,
volume, or pressure, then the system readjusts
itself to counteract the effect of the change
and a new equilibrium is established.
Application of Le Chatelier’s Principle
Le Chatelier’s Principle is a fine
summary of what chemists do.
One important example of the
principle is that of Fritz Haber.
Haber found a way to create
artificial fertilizer and boost farm
production around the world.
Plants and Nitrogen
Plants need nitrogen to grow, but cannot uptake
nitrogen from the air.
Symbiotic Relationships
If we protect and nurture the mycorrhizal fungi and
rhizobium that take nitrogen from the air, then plants
grow bigger, and faster… a big deal for farming.
The Haber Process & Le Chatelier
However, around the turn of the 20th century (circa 1900)
human farming was proceeding at a pace that exceeded
what mycorrhizal fungi and rhizobium could provide
naturally.
Fritz Haber invented a way to artificially capture
nitrogen from the air and convert it to “fertilizer”.
Fritz invented the Haber process, which is an
application of Le Chatelier’s Principle.
Applying Le Chatelier’s Principle
“When a system at equilibrium is subjected to change in
concentration, temperature, volume, or pressure, then
the system readjusts itself to counteract the effect of
the change and a new equilibrium is established.”
The Haber Process involves:
Stoichiometry
Stoichiometry is the study of the relationship between
quantities of substances taking part in a chemical reaction.
These quantities are expressed as a ratio of whole integers.
Or… the atoms on the left side of a chemical reaction must be
equal in number to the atoms on the right side.
Stoichiometry is related to the Law of Conservation of Mass.
This principle and law were both
discovered by Antoine Lavoisier.
Stoichiometry
The left side and right side of the chemical reaction must
have equal amounts of each element.
We fix the problem by adding prefixes or coefficients.
Stoichiometry
After adding prefixes to the O2 and the H2O count the
atoms on the left and right again. Are they equal now?
Stoichiometry
For example…
Can We Really Count Atoms?
We cannot really count atoms or molecules. But…
A chemist named Lorenzo Romano Amedeo Carlo Avogadro di
Quaregna e di Cerreto found a way to counts lots of atoms.
Amedeo Avogadro discovered that 6.022 x 1023 atoms of any
element is equal to the mass number of that element, in grams.
If you have 6.022 x 1023 of a thing you have one mole (or 1 mol)
of that thing.
Moles & Prefixes
The prefixes in chemical reactions do not refer to numbers of
atoms or molecules, they in fact refer to moles of that substance.
How many moles of methane?
How many moles of water?
Keep it Simple: Moles
One mole of He is 4.003 grams.
One mole of Ne is 20.180 grams.
Two moles of Ar is 80 grams.
One mole of Kr is ______ grams.
One mole of Xe is ______ grams.
Two moles of Rn is ______ grams.
Let’s Practice: Calculating Moles
1 mole of any atom is equal to its mass number, in grams
Using a periodic table, determine how many grams are in:
1. One mol of carbon atoms.
2. Two mol of calcium atoms.
3. One mol of carbon dioxide…
For molecules, we must add all of the weights
for each of the atoms involved.
Exit-Ticket: Stoichiometry & Moles
If your cell phone comes out you get a zero. Work alone & quietly.
Open notebook – Part 1 of 3 (10 Minutes)
Answer in your bell-ringer notebook in complete sentences.
1. Which of the following chemical reactions is correctly balanced:
A. MgO  Mg + O2
B. 2MgO  Mg + O2
C. 2MgO  2Mg + O2
2. Which of the following chemical reactions is correctly balanced:
A. HCl + NaOH  H2O + NaCl
B. HCl + 2NaOH  H2O + 2NaCl
C. 2HCl + NaOH  2H2O + NaCl
3. Which of the following chemical reactions is correctly balanced:
A. 2CO2 + 2H2O  C6H12O6 + 2O2
B. 3CO2 + 3H2O  C6H12O6 + 3O2
C. 6CO2 + 6H2O  C6H12O6 + 6O2
Exit-Ticket: Stoichiometry & Moles
If your cell phone comes out you get a zero. Work alone & quietly.
Open notebook – Part 2 of 3 (10 Minutes)
Answer in your bell-ringer notebook in complete sentences.
(Use three significant figures.)
4. How many grams are 1 mol of chromium (Cr) atoms?
5. How many grams are 3 moles of beryllium (Be) atoms?
6. How many grams are 1 mol of methane (CH4) molecules?
7. How many grams are 2 moles of water (H2O) molecules?
Exit-Ticket: Stoichiometry & Moles
If your cell phone comes out you get a zero. Work alone & quietly.
Open notebook – Part 3 of 3 (5 Minutes)
Answer in your bell-ringer notebook in complete sentences.
Identify the following reactions as either combustion, acid-base, singledisplacement, double-displacement, combination or decomposition.
8. 2C2H2 + 5O2  4CO2 + 2H2O
9. 2MgO  2Mg + O2
10. HCl + NaOH  H2O + NaCl
Limiting Reagent: Making Hamburgers
In a chemical reaction, the limiting reagent, also known as the
"limiting reactant", is the substance which is totally consumed
when the chemical reaction is complete.
What is the limiting reagent in the image?
Excess Reactant
The excess reactant is the reactant in a chemical reaction with
greater amount than necessary to react completely with the
limiting reactant.
What are the excess reactants in the image?
Theoretical Yield & Actual Yield
Theoretical yield
The theoretical yield of a reaction is the amount of product that
would be formed if the reaction went to completion.
Actual yield
Amount of a specified pure product actually obtained from a given
reaction.
Calculating Percent Yield
Calculating Percent Yield
Exit-Ticket: Theoretical Yield
If your cell phone comes out you get a zero. Work alone & quietly.
Open notebook – Part 1 of 4 (10 Minutes)
Answer in your bell-ringer notebook in complete sentences.
Determine the grams needed for each theoretical reaction.
Example:
2MgO
80.6 grams

2Mg
48.6 grams
+
O2
32.0 grams
Note the total mass before and after the reaction.
(The total mass on the left is equal to the total mass on the right.)
1. 8 Fe + S8 → 8 FeS
2. Zn + 2 HCl → ZnCl2 + H2
3. 2 H2O → 2 H2 + O2
4. HCl + NaOH  H2O + NaCl
Excess & Limiting Reactants
What are the excess reactants?
What are the limiting reactants?
For limiting and excess we are talking about reactants.
Exit-Ticket: Limiting Reagent
If your cell phone comes out you get a zero. Work alone & quietly.
Open notebook – Part 2 of 4 (10 Minutes)
Answer in your bell-ringer notebook in complete sentences.
Determine the limiting reagent in the following reactions.
5.
2C2H2 + 5O2  4CO2 + 2H2O
Theoretical: _______
Actual:
52 grams
6.
_________
150 grams
HCl + NaOH  H2O + NaCl
Theoretical: _______
Actual:
33.5 grams
7.
Zn
_________
40 grams
+ 2 HCl → ZnCl2 + H2
Theoretical: _______
Actual:
65 grams
8.
8 Fe
Theoretical: _______
Actual:
448 grams
_________
70 grams
+
S8
→ 8 FeS
_________
251 grams
Theoretical Yield
For yield we are talking about products.
Exit-Ticket: Percent Yield
If your cell phone comes out you get a zero. Work alone & quietly.
Open notebook – Part 3 of 4 (5 Minutes)
Answer in your bell-ringer notebook.
Determine the theoretical yield for each product.
9. 2C2H2 + 5O2  4CO2 + 2H2O
10. HCl + NaOH  H2O + NaCl
Determine the percent yield for the given actual yield.
11. 2C2H2 + 5O2  4CO2 +
160 grams
12. HCl + NaOH  H2O
15.5 grams
2H2O
34 grams
+
NaCl
45 grams