Transcript A Student want to prepare 250mL of .10 M NaCl solution

ACS Review
• Quick refresher of materials
• Some sample questions and short cuts
Sections in ACS prep book
to review
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Atomic Structure
Molecular Structure and bonding
Stoichiometry
States of Matter/ Solutions
Energetics
Descriptive Chemistry/ Periodicity
Laboratory Chemistry
Basics
• Dimensional analysis is very very important
– Know how to make conversions
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cent, kilo, ect.
Grams  moles (MM)
Vol  grams (density)
Vol  moles (concentration)
The periodic table
Notation and Calculation
56
26
Fe
Remember this?
26 protons
30 neutrons
26 electrons
Calculations: you may need to do weighted averages.
20% of a sample is 32grams/mol and 80% 28grams/mol
what is the average?
20x32 + 80x28 /100 = 28.8g/mol
The table
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Which has the highest electronegativity?
Which is isoelectric to X?
Which is likely to form the same structure as __ ?
What has 25 protons?
If it has 24 neutrons and a mass of 52 what is the
element?
formulas
Know how to use charges to determine
formula
Example: the correct formula for the compound formed
between Al and S?
Al+3 and S-2  Al2S3
Even more useful, use formula to
determine charge.
Example: you can’t remember if Ag has a +1 or +2 charge.
if AgCl is a formula given in the question or in some
other question, knowing Cl is -1 tells you Ag is +1
Formulas from %
• Given mass % or total mass of each element
determine empirical formula.
A sample contains 11.1% H and 88.9% O
11.2grams H (1 mol/1.001g)=moles H =11.18
88.9grams O(1 mol/16.0g)=moles O =5.55
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H2O
Reactions
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Single
Double
Composition
Decomposition
Combustion
Acid / Base
• Balance equations
know difference in
– General
– Ionic
– Net ionic
• stoichiometry
Acid base theories
• Bronsted/ lowry
• Lewis
• Arrhenius
• Protons
• electron pairs
• What’s produced in water
You should have your six strong acids and bases memorized.
HCl, HBr, HI, HNO3, H2SO4, HClO4
LiOH, NaOH, KOH, CaOH2, SrOH2, BaOH2
Why?
a) It helps identify weak acids and weak bases
b) It will help with determining solubility
•Balance equations
Yields
•Use stoichiometry
•Limiting reagents
• Grams------mole------mole------gram
• Amt------mole------mole-----amt
• Amt -------- Mole
– Grams (molar mass)
– Liters of solution (concentration)
– Gas (Ideal gas law)
Solution
•Molarity(M) Vs Molality(m)
mole
L of solution
Total solution solvent and solute
Dilution:
C1V1=C2V2
m ole
Kg of solvent
Solvent only
Titration:
naMaVa=nbMbVb
Gas laws
• PV=nRT
– Mostly the relationships (when P goes from 1020, V does what?)
• Remember T is in K
– When gases are non ideal (correct for molecular
volume and intermolecular forces)
– Diffusion small things faster
Structure
• Quantum numbers
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n
l
ml
s
is the major shell(1,2,3…
is the subshell (0=s, 1=p)
is the axis (x, y, z)
spin (+ ½ )
• Filling the orbital (use the table)
Bonding and geometry
• Ionic vs. Covalent
• Electronic vs. Molecular geometry (VSEPR)
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Drawing Lewis structures
Dipoles
Hybrids
Pi bonds
MO
Delocalized bonds (resonance)
Lewis structures
• Multiple Choice Test Just be able to pick the
correct drawing!!
• Some things to look for
– Octets on non-central atoms (all atoms if central is 1st row)
– Happy elements
– Charges
• Negative usually carried by single bonded O (one for each charge)
• Positive usually carried by a four bond N or P
O -1
O
N
Cl
O
O Cl O
O
-3
O
O
P
O
O
H
+1
H N H
H
States of matter
Know the basic properties
Remember this:
Freezing / melting
Liquid
Solid
Condensing / boiling
Gas
Sublimation / Deposition
Triple point
energy
– Heat of formation ( to form from the elements)
 DHf of MgCl2 is Mg(s) + ½ Cl2(g)  MgCl2 DH=___kJ
– Heat of combustion(react with O2)
 DH of CH4 is CH4 + 2O2(g)  CO2 + 2H2O DH=___kJ
Solid at STP
Diatomic gas at STP
State function have D which means final - initial
Energy
Bond Enthalpy = Sum of bond energy of
reactants - sum of bond energy of products
(Breaking bonds- forming bonds)
Enthalpy of reaction using DHf= sum of
products – sum of reactants
Hess’s Law===Get to the goal by
manipulating reaction information given and
adding up the reactions used
When Solving Problems
• Look for the easiest way to solve! There
are 70 questions and only 110 minutes so
THERE MUST BE SHORT CUTS!
1.
Which of these compounds contains the greatest
percentage of nitrogen?
A) C6H3N307
B) CH4N20
C6H3N307 229 g/mol
C) LiNH2
CH4N20
60.1 g/mol
D) Pb(N3)2
LiNH
23.0 g/mol
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Pb(N3)2
229.1 g/mol
The long way: calculate the %N for each one
mass N
x100
total mass
The quicker way: all N have the same mass so,
Which has the highest N to mass ratio or Even better
which has the lowest total mass per N
A cursory glance tells us it is not B or A
D has 6 N it may need a second look 229/6=38
The answer is C
The Number of atoms in 9.0g of Aluminum is equal to the
Number of atoms in
A) 8.1g Mg
B) 12.1g Mg The Long way:
C) 9.0g Mg Calculate # of atoms in 9.0 g Al
D) 18.0g Mg Then calculate mass of that # of Mg atoms
Look for ratios: Al has a molar mass of 27
This is 1/3 of a mole Al
Which one is 1/3 mole of Mg
24.3 x 1/3 = 8.1g
So “A”
When NF3 and BF3 are reacted together they form BF3NF3
what is the geometry of the B and N atoms.
A) Both tetrahedral
B) B is triganal planer and N is tetrahedral
C) Both triganal planer
D) N is triganal planer and B is tetrahedral
How many things are around each?
B and N each will have 4 bonds
Both tetrahedral
A student wants to prepare a 250mL sample of 0.10 M NaCl.
Which procedure is the most appropriate?
Molar mass of NaCl 58.4 g ·mol-1
A) Add 5.84g NaCl to 250mL of water
B) Add 1.46g of NaCl to 250mL of water
C) Dissolve 5.84g of NaCl in 50mL and Dilute to 250mL
D) Dissolve 1.46g of NaCl in 50mL and Dilute to 250mL
Mol/L of solution
¼ L of 0.1M
So A and B are out
5.84 is 0.1 mole NaCl
1.46 is ¼ of that
So “D”
The oxidation number of chlorine in KClO3 is
a) +6
b) +5
c) -1
d) -2
e) +2
O only oxidation is –2 (unless peroxide)
3 x -2 = -6
K only oxidation +1
1 x +1 =+1
-5
+5 to Balance it out
B
Which one of the following sets of quantum numbers is not
allowed?
a) n = 3, l = 2, ml = +1
b) n = 3, l = 3, ml = 0
c) n = 3, l = 0, ml = 0
d) n = 4, l = 3, ml = -2
l must be less than n
ml absolute value must be less than or equal to l
B
Which ion has 26 electrons?
a)
b)
c)
d)
Cr+2
Fe+2
Ni+2
Cu+2
Its really asking “Which is iso-electronic to Fe?”
On the table “What minus 2 electrons looks like iron?”
C  Ni+2
Element X has two isotopes 13X with 80% abundance
and 12X with 20% abundance, what is the average
mass of the element?
a) 12. amu
b) 12.8 amu
c) 12.5 amu
d) 13.0 amu
Long way: (13 X 80) + (12 X 20)/100
But why bother:
the weighted average will be
closer to the larger abundance
B
GOOD LUCK!!!
• 10 AM class your final is Friday April 27 at
8 am in LCTR 346
• 11 AM class your final is Monday April 30
at 8 am in LCTR 346
• You must get permission to switch from one
time to another.
SI sessions and Office Hours
• SI sessions in RHSC 317 Tuesday at 5 pm
and Wednesday 8 pm
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– Wednesday (April 25th)11-4
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