Upload
edgar-allison
View
212
Download
0
Embed Size (px)
Citation preview
1
Test 2 Study Guide
Thursday February 26
8:00 p.m. Dobo 134
2
What’s it on?
• End of C 3 (page 91 forward)
• Chapter 4 (except (4.4 – oxidation reduction pages 128-133 and titrations pages 140-143)
• Chapter 5 through 5.5 ( page 174)*
• Calorimetry will now be on this test*
* Updated Feb 17, 2004
3
What should I do?
• Do the first problems on the practice sheet I handed out
• Study the practice exam on the web (skip questions 18-20)
4
Top 8 Topics
• Empirical Formula from weight %• Limiting reactants• Ionic compounds in water• Strong/weak acids & bases• Moles• Molarity• Energy• Enthalpy
5
Empirical Formula from weight %
• Given mole ratio, be able to convert to whole number ratio to get empirical formula
• Give mass ratio – either as grams or as a percent – be able to convert to moles and then convert mole ratio to whole number ratio to get empirical formula
6
Limiting Reactants
• Theoretical Yield
• % Yield = (Actual/Theoretical) x 100
• How much is used, formed, left over
7
Ionic Compounds
• In water
• Strong / weak electrolytes
• Ionic equations
• Metathesis reactions
• Ion Solubility
8
Strong acids & bases• Strong acids/bases are strong electrolytes
• Common strong acids (Table 4.2) (memorize) – HCl HBr HI HClO3(chloric) HClO4
(perchloric) HNO3 H2SO4
• Common strong bases– Group I metal hydroxides (LiOH, NaOH, KOH,
RbOH, CsOH)
– Heavy Group II metal hydroxides Ca(OH)2, Sr(OH)2 Ba(OH)2
9
Weak acids & bases• Weak acids/bases are weak electrolytes
• An acid or base that is not strong is weak
• Examples of weak acids:– HF H3PO4 H2SO3 HC7H5O2 HC2H3O2
• Example of a weak base: NH3
• A molecular substance that is not an acid or base is a nonelectrolyte
10
Moles
• Be able to interconvert mass to moles and moles to mass
• How many atoms in 3 g H2 ?
• (1 Mole H2 / 2 g H2) (3 g H2) (2 moles atoms / Mole H2 ) =
3 moles atoms
= 18 x 1023 atoms = 1.8 x 1024 atoms
11
Molarity
• Interconverting molarity, moles, volume
• Dilution
12
Energy
E = q + w
13
Enthalpy
• Endo , exo, sign of H
• Given heat for a certain mass, calculate reaction H
• Given H and mass, calculate heat
14
Top 8 TopicsLet’s do some examples!
• Empirical Formula from weight %• Limiting reactants• Ionic compounds in water• Strong/weak acids and bases• Moles• Molarity• Energy• Enthalpy
15
A compound is 76.6%C; 6.38%H; and 17.0%O. What is the empirical formula?
• Divide by atomic weight to get mole ratio:– 76.6 / 12 = 6.38– 6.38/1 = 6.38– 17.0/16 = 1.06
• Divide mole ratio by smallest number to get whole number ratio– 6.38 /1.06 = 6.02– 6.38 / 1.06 = 6.02– 1.06 / 1.06 = 1
• Empirical formula is C6H6O
16
Limiting Reactants
• Theoretical Yield – how much you expect based upon the amount of reactants.
• If one reactant is present in excess, then the other limits how much can be made and is used to determine the theoretical yield.
17
2H2 + O2 2 H2O• If 10 moles of oxygen and 10 moles of hydrogen….• The hydrogen limits the amount of water that can be
formed
• Based upon 10 moles H2, we can make 10 moles water
• Based upon 10 moles O2, we can make 20 moles water.
• H2 limits. Theoretical Yield = 10 moles ( 180 g) H2O
• At end of reaction, will have 5 moles O2 left over
18
Ionic Compounds
• In water
• Strong / weak electrolytes
• Ionic equations
• Metathesis reactions
• Ion Solubility
19
• Group 1A ( alkali metals) cations soluble
• NH4+ soluble
• NO3- soluble
• CH3CO2- = C2H3O2
- = acetate soluble
• Will be given a chart for other ions
20
• Soluble ionic compounds in water exist as free ions surrounded by water molecules.
• Soluble ionic compounds are strong electrolytes
• Strong acids or bases (HCl, H2SO4), NaOH) are strong electrolytes
• Weak acids or bases (CH3CO2H, acetic acid) are weak electrolytes
• Molecules that do not disassociate (CO2, sugar) are non electrolytes.
21
What kind of electrolyte am I?
• (NH4)2SO4 ?
• Strong• HF• Weak
• C12H22O11 (sucrose)
• Non
• NH3
• Weak
22
potassium sulfate with barium nitrate
• 2K+(aq) + SO4-2 (aq) + Ba+2 (aq) + 2 NO3
- (aq)
2K+(aq) + 2 NO3- (aq) +BaSO4(s)
• SO4-2 (aq) + Ba+2 (aq) BaSO4(s)
23
Molarity
• Interconverting molarity, moles, volume
• M means moles per liter = moles/L
• M = moles/L
• If you know two things, can determine the third
• If you have moles and volume, can determine molarity
• 3 moles dissolved in 0.5 L = 3moles/0.5L = 6M
24
Molarity - dilution
• (Vconc )(Mconc ) = (Vdil )(Mdil )
• If you know 3, can solve for the fourth• How many mL of 3M HCl is needed to make
100mL of 1.5 M HCl?
• (Vconc)(3M) = (100mL)(1.5M)
• Vconc = 50 mL
25
E = q + w• q > 0 heat transferred from the surroundings to
the system (endothermic)• q < 0 heat transferred from the system to the
surroundings ( exothermic)• w > 0 work is done by the surroundings on the
system• w < 0 work is done by the system on the
surroundings• q > 0, w > 0 E > 0• q < 0, w < 0 E< 0
26
Enthalpy
• Endothermic H > 0
• Exothermic H < 0
27
Given heat for a certain mass, calculate reaction H
• If it takes 60 kJ to melt 180 grams of ice, what is H for the following reaction?
• H2O(s) H2O(l)
• (60kJ / 180g) ( 18 g/mole) = 6 kJ/moleH = 6kJ
28
Given H and mass, calculate heat
H2O(s) H2O(l) H = 6 kJ
How much heat is needed to melt 900 grams of ice?
(900g)(6 kJ/mole)(1mole/18 g) = 300 kJ