Download Praxis II Chemistry prep

Praxis II Chemistry prep
Karen M. Morris
Univ. of Notre Dame
[email protected]
631-6945
The Atom
What we observe vs. What we represent
6
C
Carbon
12.011
12
6
C
C
C
13
6
14
6
Let’s Practice
1. Explain why atomic
weights of elements
often differ markedly
from whole numbers.
3. In what way do the
isotopes of a given
element differ?
2. Determine the number
of protons, electrons and
neutrons in each:
235
92
U
22
10
Ne
59
28
Ni
1. Explain why one of
the following is not
a property of an
element:
a. boiling point
b. density
c. volume
The Periodic Table
What we observe vs. What we represent
115
Ds
Rg
Cn
Uut Uuq
Uup
116
Uuh
117
118
Uuo
Let’s Practice
1. Compare the atomic size of row 4 elements to row 5
elements. Describe the general trend as one goes from left
to right across the periodic table.
1. Arrange the following ions in order of increasing
size: Mg2+, Na+, Al3+
1. In the following pairs of ions, identify which is
most likely to exist and explain why you think so.
Ca2+ or Ca2S2+ or S24. Why is the radius of a positive ion smaller than
the radius of its parent atom?
Chemical Formulae and
Equations
What we observe vs. What we represent
Forming Chemical Compounds
Ionic
Covalent
Writing Chemical Equations
Law of Conservation of Matter
Let’s Practice
1. The chemical formula of the compound dopamine is
C8H11O2N
Would you expect this to be an ionic or covalent compound?
Explain…
1. Identify the pure compound as ionic or covalent:
HCl CuBr2
F2
Na3PO4
CCl4
AgCl
Let’s Practice
1. Balance the following chemical equations
a. H2 + Cl2
HCl
b. Na + H2O
NaOH + H2
c. Zn + AgCl
ZnCl2 + Ag
d. KClO3
KCl + O2
Observations of Matter
1. Representations can be atoms or large quantities of atoms
2. Experimentally discovered that all large quantities
represented by one number (discovered by Avogadro) and
measured as 6.022 x 1023 atoms
3. This is DEFINED as “1 mole” of matter
4. You measure this mass quantity in grams per mole.
1 mole of C contains 6.022 X 1023 atoms and masses 12.011 g
1 mole of H contains 6.022 X 1023 atoms and masses 1.008 g
1 mole of U contains 6.022 X 1023 atoms and masses 238.029 g
Compounds
1 mole of carbon dioxide, CO2, contains
6.022 x 1023 molecules of CO2
and masses the sum of 1 Carbon plus
2 Oxygen: (12.011 g) + 2(15.99 g) = 43.99 g
A.K.A. as a “molar mass” (mass of 1 mole)
1 mole of calcium carbonate, CaCO3, contains
_________ molecules of CaCO3
and masses the sum of __________
Compounds
We can manipulate the molar mass of CO2 to determine the
mass percent of each element in the sample.
This idea is the basis of quantitative analysis of materials.
Molar Mass CO2 = (12.011 g) + 2(15.99 g) = 43.99 g
Mass % of C in the sample = [(12.011)/(43.99)] * 100 = 27.3%
Mass % of O in the sample = [2(15.99)/(43.99)]* 100 = 72.7%
or 100% - 27.3% = 72.7% (the easy way ;-)
Let’s Practice
H2O
H2 + O2
1. Something is “wrong” with this equation. Fix it.
2. After fixing it, determine the mass of each compound.
3. How many moles of hydrogen and oxygen do we get
if we break down 3 moles of water?
4. How many grams of hydrogen to we get if we break
down 3 moles of water?
5. What is the mass percent of hydrogen in water?
Let’s Practice
The chemical formula of the compound dopamine is
C8H11O2N
What is the mass percent of carbon, C, in dopamine?
What is the molar mass of dopamine?
What is the mass of 0.15 moles of dopamine?
How many moles of C are in 0.15 moles of dopamine?
How many grams of C are in 0.15 moles of dopamine?
Let’s Practice
a) H2 + Cl2
2 HCl
a) Na + 2 H2O
2 NaOH + H2
a) Zn + 2 AgCl
ZnCl2 + 2 Ag
a) 2 KClO3
2 KCl + 3 O2
Physical Properties of Matter
What we OBSERVE vs. what we REPRESENT
1. Ice cube melting
2. Melted puddle of water evaporating
Phases of matter
1. Solid
2. Liquid
3. Gas
Let’s Practice
1. Draw representations of solid, liquid and gas at the atomic
level. How are your drawings different? How the same?
1. What happens to a gas volume when it is compressed?
What happens to a liquid volume when it is compressed?
What happens to a solid volume when it is compressed?
1. What happens to a gas volume when it is heated?
What happens to a liquid volume when it is heated?
What happens to a solid volume when it is heated?
Chemical Changes
What we OBSERVE vs. what we REPRESENT
1. Observed:
a. Sometimes NOTHING!! Need instrumentation
to measure
b. Sometimes solid is formed, bubbles (gas), heat,
light
c. Reactant materials will not easily return.
2. Represented:
a. Physical rearrangement of atoms
b. Balance in number of atoms in reactants
and products.
Let’s Practice
a) H2 (g) + Cl2 (g)
2 HCl (g)
a) Na (s) + 2 H2O (l)
2 NaOH (aq) + H2 (g)
a) Zn (s) + 2 AgCl (aq)
ZnCl2 (aq) + 2 Ag (s)
a) 2 KClO3 (s)
2 KCl (s) + 3 O2 (g)
General Types of Reactions
Reaction Types:
What we OBSERVE vs. what we REPRESENT
Precipitation:
MgCl2 + 2 NaOH
Mg(OH)2 + 2 NaCl
2 clear and colorless solutions poured together and
a white solid appears
Acid-Base Neutralization:
HCl + NaOH
H2 O + NaCl
a very acidic and a very basic solution poured together
to form a clear and colorless neutral solution
(salt + water)