1 Test 2 Study Guide Thursday February 26 8:00 p.m. Dobo 134.

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Test 2 Study Guide

Thursday February 26

8:00 p.m. Dobo 134

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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

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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)

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Top 8 Topics

• Empirical Formula from weight %• Limiting reactants• Ionic compounds in water• Strong/weak acids & bases• Moles• Molarity• Energy• Enthalpy

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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

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Limiting Reactants

• Theoretical Yield

• % Yield = (Actual/Theoretical) x 100

• How much is used, formed, left over

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Ionic Compounds

• In water

• Strong / weak electrolytes

• Ionic equations

• Metathesis reactions

• Ion Solubility

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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

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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

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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

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Molarity

• Interconverting molarity, moles, volume

• Dilution

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Energy

E = q + w

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Enthalpy

• Endo , exo, sign of H

• Given heat for a certain mass, calculate reaction H

• Given H and mass, calculate heat

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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

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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

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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.

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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

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Ionic Compounds

• In water

• Strong / weak electrolytes

• Ionic equations

• Metathesis reactions

• Ion Solubility

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• Group 1A ( alkali metals) cations soluble

• NH4+ soluble

• NO3- soluble

• CH3CO2- = C2H3O2

- = acetate soluble

• Will be given a chart for other ions

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• 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.

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What kind of electrolyte am I?

• (NH4)2SO4 ?

• Strong• HF• Weak

• C12H22O11 (sucrose)

• Non

• NH3

• Weak

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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)

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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

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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

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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

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Enthalpy

• Endothermic H > 0

• Exothermic H < 0

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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

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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