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Chapter 4 Types of Chemical Reactions And Solution Stoichiometry.

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1 Chapter 4 Types of Chemical Reactions And Solution Stoichiometry

2 Section 4.1: Water, The Common Solvent Hydration of an ionic compound will occur when the partial positive end of a water becomes attracted to the anions in the compound; likewise for the partial negative center of the water and the cations. Solubility depends on the strength of the intermolecular attractions between the ions and water, as well as the intramolecular attractions of the cations and anions of the compound. NH 4 NO 3(s)  NH 4 + (aq) + NO 3 - (aq)

3 What can dissolve in H 2 O? Soluble Soluble Alcohols Alcohols ex: C 2 H 5 OH ex: C 2 H 5 OH Sugars Sugars ex: C 6 H 12 O 6 ex: C 6 H 12 O 6 Ionic compounds Ionic compounds ex: NaCl, KOH, LiBr Insoluble Insoluble Fats ex: bacon grease Oils ex: cooking oil Non-Polar Substances ex: turpentine Because of intermolecular forces: the OH group on the sugars and alcohols is particularly attractive to a water molecule. Generally speaking: “Like Dissolves Like”

4 Section 4.2: Strong and Weak Electrolytes Solute + Solvent = Solution Solute + Solvent = Solution Strong electrolytes conduct electricity Strong electrolytes conduct electricity Weak electrolytes barely conduct electricity Weak electrolytes barely conduct electricity Conductivity depends upon ionization Conductivity depends upon ionization

5 Strong Electrolytes Strong Electrolytes Soluble salts Soluble salts Strong acids Strong acids Strong bases Strong bases All of these dissociate completely in water. Weak Electrolytes Weak Electrolytes Weak acids Weak bases All of these partially dissociate in water HCl  H + + Cl - NaOH  Na + + OH - HC 2 H 3 O 2 H + + C 2 H 3 O 2 Non-Electrolytes Non-Electrolytes are completely molecular substances in water (not even a little dissociation); Non polar substances.

6 Section 4.3: Composition of Solutions Concentration is measured in molarity, molality, and many others. Concentration is measured in molarity, molality, and many others. Concentration DOES NOT directly express the number of ions present in a solution. Concentration DOES NOT directly express the number of ions present in a solution. M= moles solute liters solution M= moles solute liters solution MgCl 2  Mg Cl M 1.0 M 2.0 M

7 Sample Problems Calculate the number of moles of Cl - ions in 1.75 L of 1 x M ZnCl 2. Calculate the number of moles of Cl - ions in 1.75 L of 1 x M ZnCl 2. A chemist needs 1.0 L of 0.20 M K 2 Cr 2 O 7 solution. How much solid K 2 Cr 2 O 7 must be weighed out to make this solution?

8 Standard Solution: a solution whose concentration is accurately known. Standard Solution: a solution whose concentration is accurately known. Example: M HCl; M NaOH Example: M HCl; M NaOH Creating dilutions Creating dilutions Chemical analysis of a compound Chemical analysis of a compound Theoretical Calculations Theoretical Calculations ANSWERNOW What would you do to prepare a standard solution? In your answer, include specific pieces of glassware, techniques, or equipment you should use.

9 Dilutions Dilution is the process used to make the solution less concentrated. Dilution is the process used to make the solution less concentrated. moles before dilution = moles after dilution moles before dilution = moles after dilution Because M =mol/L, V 1 (M 1 ) = V 2 (M 2 ) Lab Technique: Use a pipet to deliver the correct amount of original solution to a volumetric flask. Add some water, swirl. Fill to line, invert.

10 DONOW You have a large quantity of 1.5 M NaOH solution available. Dilute this to 100.0mL of a 0.05 M solution. Submit your calculations and store your final product for use in our first lab.

11 Section 4.4: Types of Chemical Reactions There are more than just these few types, but in this chapter we will cover… Precipitation Precipitation Acid-base Acid-base Oxidation-Reduction Oxidation-Reduction

12 Section 4.5: Precipitation Reactions Precipitation Reactions (double displacement) Precipitation Reactions (double displacement) Forms a solid precipitate from aqueous reactants. Forms a solid precipitate from aqueous reactants. Color of precipitate can help in identification Color of precipitate can help in identification Solubility rules help BUNCHES Solubility rules help BUNCHES MORE…

13 Solubility RULES All compounds containing alkali metal cations and the ammonium ion are soluble. All compounds containing alkali metal cations and the ammonium ion are soluble. All compounds containing NO 3 -, ClO 4 -, ClO 3 -, and C 2 H 3 O 2 - anions are soluble. All compounds containing NO 3 -, ClO 4 -, ClO 3 -, and C 2 H 3 O 2 - anions are soluble. All chlorides, bromides, and iodides are soluble except those containing Ag +, Pb 2+, and Hg 2+. All chlorides, bromides, and iodides are soluble except those containing Ag +, Pb 2+, and Hg 2+. All sulfates are soluble except those containing Hg 2+, Pb 2+, Sr 2+, Ca 2+, and Ba 2+. All sulfates are soluble except those containing Hg 2+, Pb 2+, Sr 2+, Ca 2+, and Ba 2+. All hydroxides are only slightly soluble, except those containing an alkali metal, Ca 2+, Ba 2+,and Sr 2+. NaOH and KOH are the most soluble hydroxides. All hydroxides are only slightly soluble, except those containing an alkali metal, Ca 2+, Ba 2+,and Sr 2+. NaOH and KOH are the most soluble hydroxides. All compounds containing PO 4 3-, S 2-, CO 3 2-, and SO 3 2- are only slightly soluble except for those containing alkali metals or the ammonium ion. All compounds containing PO 4 3-, S 2-, CO 3 2-, and SO 3 2- are only slightly soluble except for those containing alkali metals or the ammonium ion.

14 Practice Predicting Potassium nitrate and barium chloride Potassium nitrate and barium chloride Sodium sulfate and lead (II) nitrate Sodium sulfate and lead (II) nitrate Potassium hydroxide and iron (III) nitrate Potassium hydroxide and iron (III) nitrate

15 ALL REACTIONS SHOULD BE WRITTEN IN NET IONIC FORM

16 Section 4.7: Stoichiometry of Precipitation Reactions Stoichiometry in a precipitation reaction is performed just like stoichiometry for a molecular reaction. Stoichiometry in a precipitation reaction is performed just like stoichiometry for a molecular reaction. You need to know which ion comes from which molecular formula. You need to know which ion comes from which molecular formula.

17 Sample problem Calculate the mass of solid NaCl needed to add to 1.5 L of 0.1 M silver nitrate solution to precipitate all Ag + ions in the form of AgCl. Calculate the mass of solid NaCl needed to add to 1.5 L of 0.1 M silver nitrate solution to precipitate all Ag + ions in the form of AgCl. Net Ionic Eq: Ag + + Cl -  AgCl

18 General Format Write the Net Ionic Equation Write the Net Ionic Equation Calculate the moles present Calculate the moles present Identify the Limiting Reactant* Identify the Limiting Reactant* Use Mole Ratio(s) Use Mole Ratio(s) Fancy-fy your answer (put in correct units) Fancy-fy your answer (put in correct units)

19 Try Me! What mass of precipitate will be produced when 50.0 mL of 0.200M aluminum nitrate is added to mL of M potassium hydroxide? What mass of precipitate will be produced when 50.0 mL of 0.200M aluminum nitrate is added to mL of M potassium hydroxide?

20 Section 4.8: Acid-Base Reactions Definitions of acid and base vary. Definitions of acid and base vary. Arrhenius and Bronsted/Lowry are common theories. Arrhenius and Bronsted/Lowry are common theories. Acid-Base rxns are called NEUTRALIZATIONS Acid-Base rxns are called NEUTRALIZATIONS Acids yield H + Bases yield OH - Acids are proton donors Bases are proton acceptors

21 Strong Acid-Strong Base (HCl) (NaOH) Both dissociate completely H + + OH -  H 2 O Na + and Cl - are spectators. Weak Acid - Strong Base (HC 2 H 3 O 2 ) (KOH) Acetic acid will not dissociate KOH will completely HC 2 H 3 O 2 + OH -  H 2 O + C 2 H 3 O 2 - K + is a spectator.

22 Stoichiometry sample What volume of M HCl is needed to neutralize 25 mL of 0.35 M NaOH? What volume of M HCl is needed to neutralize 25 mL of 0.35 M NaOH? H + + OH -  H 2 O

23 Titrations…define me! Volumetric analysis Volumetric analysis Titration Titration Titrant Titrant Analyte Analyte Equivalence point Equivalence point Indicator Indicator Endpoint Endpoint

24 To complete a successful titration… 1. The reaction between the titrant and the analyte should be known (you should know WHAT substances you have) 2. The equivalence point should be marked accurately (you should use the right indicator) 3. Volume of the titrant needed to reach the equivalence point should be recorded accurately (you should use a buret!)

25 Effective Indicator Ranges

26 Titration Try Me Calc 1 A 50.0 mL sample of a sodium hydroxide solution is to be standardized M of KHP (potassium hydrogen phthalate, KHC 8 H 4 O 4 ) is used as the titrant. KHP has one acidic hydrogen mL of the KHP solution is used to titrate the sodium hydroxide solution to the endpoint. What is the resulting concentration of the analyte?

27 Titration Try Me Calc 2 How many milliliters of a M sodium hydroxide solution are needed to neutralize 20.0 mL of a M sulfuric acid solution? How many milliliters of a M sodium hydroxide solution are needed to neutralize 20.0 mL of a M sulfuric acid solution?

28 Norton Tutorial Go to the website /chemistry3/ch/17/chemtours.aspx Go to the website /chemistry3/ch/17/chemtours.aspx /chemistry3/ch/17/chemtours.aspx /chemistry3/ch/17/chemtours.aspx Find the tutorial on Acid/Base ionization. Find the tutorial on Acid/Base ionization. Complete the tutorial question form. Complete the tutorial question form.

29 Section 4.9: Redox Reactions What is it?? -A reaction that occurs in conjunction with a transfer of electrons. We assign oxidation states to individual atoms in a reaction to observe the change in electrons. Oxidation states are written with the +/- sign before the quantity. Ion charges are written with the +/- sign behind the quantity.

30 The Oxidation State of… Quantity of Oxid. State Examples An atom in element form ZeroNa (s), O 2(g) A monatomic ionEqual to the charge on the ion Na +, Cl - Fluorine in a compound -1, alwaysHF, PF 3 Oxygen in a compound - 2, except in peroxide where it is -1 H 2 O, CO 2, H 2 O 2 Hydrogen in a compound +1, alwaysH 2 O, HCl, NH 3

31 Oxidation= an increase in the oxidation state Oxidation= an increase in the oxidation state Reduction = a decrease in the oxidation state Reduction = a decrease in the oxidation state 2Na (s) + Cl 2(g)  2NaCl (s) oxidation reduction

32 The metal is oxidized and the other substance is reduced. The metal is oxidized and the other substance is reduced. Metal Atom Metal Ion Other Ion Other Atom e- Oxidized Substance: Loss of electronsLoss of electrons Oxidation state increasesOxidation state increases Gets SmallerGets Smaller Called the Reducing AgentCalled the Reducing Agent Reduced Substance: Gain of electronsGain of electrons Oxidation state decreasesOxidation state decreases Gets BiggerGets Bigger Called the Oxidizing AgentCalled the Oxidizing Agent

33 Section 4.10: Balancing Redox 1. Write the ½ reactions 2. Balance the non-H and non-O atoms 3. Balance O by adding H 2 O where needed 4. Balance H by adding H + where needed 5. Balance charge using e- 6. Multiply by coefficients until both e- are equal for each ½ reaction 7. Add the ½ reactions together (cancel stuff)

34 Redox Sample Problem Balance: MnO Fe 2+  Fe 3+ + Mn 2+ Check Charges! x5! x5!

35 Redox Try Me Problem As 2 O 3(s) + NO 3 -  H 3 AsO 4 + NO (g)

36 1. Repeat steps from old procedure 2. Cancel out H + by adding OH - ions 3. Re-write H + and OH - as water 4. Add ½ reactions together (and cancel stuff)

37 Redox Try Me Problem 2 Balance, in base: Ag (s) + CN - + O 2  Ag(CN) 2 -


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