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9.1 General Properties of Aqueous Solutions Electrolytes and Nonelectrolytes

9.1 General Properties of Aqueous Solutions Electrolytes and Nonelectrolytes 9.2 Precipitation Reactions Solubility Guidelines for Ionic Compounds in Water Molecular Equations - Ionic Equations - Net Ionic Equations 9.3 Acid-Base Reactions Strong Acids and Bases

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9.1 General Properties of Aqueous Solutions Electrolytes and Nonelectrolytes

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  1. 9.1 General Properties of Aqueous Solutions Electrolytes and Nonelectrolytes 9.2 Precipitation Reactions Solubility Guidelines for Ionic Compounds in Water Molecular Equations - Ionic Equations - Net Ionic Equations 9.3 Acid-Base Reactions Strong Acids and Bases Brønsted Acids and Bases Acid-Base Neutralization 9.4 Oxidation-Reduction Reactions Oxidation Numbers Balancing Simple Redox Equations Other Types of Redox Reactions 9. Reactions in aqueous solution 9.5 Concentration of Solutions Molarity - Dilution Solution Stoichiometry 9.6 Aqueous Reactions and Chemical Analysis Acid-Base Titrations

  2. Many chemical reactions occur in solutions Solution = a mixture of two or more compounds mixture implies that they need not be in fixed proportions Solvent = the component of a solution present in greater amount Solute = the component(s) of a solution present in lesser amounts Aqueous solution = A solution with water as the solvent Types of chemical reactions • Precipitation reaction (typically involves ionic compounds) • Acid-base reactions • Oxidation – reduction reactions (redox reactions)

  3. Electrolytes A compound that produces ions when it dissolves in water is an electrolyte Solutions may be classified according to their ability to conduct electricity as …... Strong Electrolytes – fully dissociate in solution …… e.g. soluble ionic compounds MgCl2(s) (add water) → Mg2+(aq) + 2Cl-(aq). strong acids HCl (added to water) → H+(aq) + Cl-(aq). nonelectrolytes – may dissolve but do not “ionize” in aqueous solution. e.g. Glucose(s) (add water) ↔ Glucose(aq) Weak electrolytes – partially dissociate in solution …… e.g. weak acids CH3-COOH (added to water) ↔ H+(aq) + CH3-COO-(aq). acetic acid proton acetate ion. mostly some

  4. electrolyte ― A substance that dissolves in water to produce a solution that conducts electricity. include soluble ionic compounds and strong acids nonelectrolyte― Will not conduct electricity when dissolved in water. most molecular compounds (excluding strong acids) Non electrolyte weak electrolyte strong electrolyte

  5. Solubility - What does it mean to dissolve? Water (H2O) .. H – O – H ̈ Like dissolves Like NaCl(s) + H2O(l) → Na+(aq) + Cl- (aq) .. :O Cl- Na+ + - + - + - + - + - + - + - + - + - + - + - + - + - + - + - + - H H The interaction between a hydrated ion (either + or -) is called an ion-dipole interaction. Ions dissolved in water are called electrolytes. An NaCl solution conducts electricity, but a glucose solution will not.

  6. Molarity(M) = moles solute Liter of solution Solution stoichiometry: The amounts of solution reagents is measured by volume rather than mass. To do reaction stoichiometry we need to know how much of the solute was present in the measured volume. Solution concentration amount of solute amount of solution concentration units Molarity = Moles of solute per liter of solution Molality = moles of solute per kg of solvent Mole fraction = moles of solute per total moles of solution components % by weight = mass of solute  mass of solution • 100

  7. Molarity(M) = moles solute Liter of solution 1. Add solute to flask 2. Add solvent to mark (solute must be dissolved) 10.0 grams of glucose (C6H12O6 – 180 g mol-1) is added to a 500 ml flask. Water is added to the mark and the glucose dissolves. What is The concentration of the glucose solution? 0.5 Liter 10.0 g glu x 1 mol glu = 0.111 mol/L or Molar or M 0.5 L soln. 180 g glu

  8. Dilution Calculations In a lab solutions are often prepared at a higher concentration than they are used. The higher concentration solution is often referred to as the stock solution. The solution required is prepared from the stock solution by dilution. Dilutions always use the following equation ….. C1V1 = C2V2 C = concentration (any units may be sued as long as they match on both side of the equation) V = Volume (any units may be used as long as they match on both side of the equation) 1 = stock solution 2 = diluted solution

  9. 3.20 g of (NH4)2CO3 (96.0 g/mol) is diluted to a final volume of 200. ml. What is the [(NH4)2CO3] in Molarity? a. 0.167 M b. 0.975 M c. 0.0390 M d. 0.640 M 3.20 g (NH4)2CO3•1 mol = 0.200 L 96.0 g 0.167 M 10.0 ml of this solution is added to 25.0 ml of water. (assume additive volumes) What is the [(NH4)2CO3] in the diluted solution? a. 0.195 M b. 0.0195 M c. 0.0477 M d. 0.477 M M1 V1 = M2V2 0.167 M • 10.0 ml = M2• 35.0 ml M2 = 0.0477 M

  10. Solubility Guidelines (abbreviated) Precipitation reactions Ca(NO3)2(aq) + Na2CO3(aq)→ ? CaCO3(s) + 2NaNO3(aq) A solution contains Ba2+ and Pb2+ : What would you add to separate these ions? a. K2S b. Na2CO3 c. KOH d. NaNO3

  11. Molecular (Formula unit) Equation Ca(NO3)2(aq) + Na2CO3(aq)→ CaCO3(s) + 2NaNO3(aq) Spectator ions equation ionic equation Ca2+(aq) + 2NO3-(aq) + 2Na+(aq) + CO32-(aq) → Ca2+(aq) + CO32-(aq) → CaCO3(s) CaCO3(s) + 2Na+(aq) + 2NO3-(aq) Net ionic equation

  12. 1. Write/balance reaction (as needed) • Determine the # moles of all reagents given 3. Determine the # moles of the requested reagent. 4. Determine the # grams/concentration of the requested reagent. Solution Stoichiometry How many grams of CaCl2 are needed to precipitate all of the Ag+ ions in a 250. ml of a 0.0113 M AgNO3 solution? __AgNO3(aq)+ __CaCl2(aq)→ __Ca(NO3)2(aq)+ __AgCl(s) 2 1 1 2 0.0113 mol AgNO3 x 0.250 L AgNO3 1 L AgNO3 x 1 mol CaCl2 2 mol AgNO3 x 111 g CaCl2 = 1 mol CaCl2 0.157 g CaCl2 What is the final [Ca(NO3)2] and the amount of AgCl produced if 50. ml of 0.0113M AgNO3 is mixed with 50. ml of 0.0085M CaCl2?

  13. : : O H H proton H2O  H+ + OH- H2O+ H2O  H3O+ + OH- hydronium ion Water Water is amphoteric. Water & Arrhenius, Brønsted, & Lewis acid/base

  14. Acids: sour taste e.g. vinegar (acetic acid) lemon (citric acid) Bases: bitter taste e.g. numerous herbs slippery feel e.g. soap AcidsBases Arrhenius proton donor hydroxide ion donor Brønsted proton donor proton acceptor Lewis electron pair acceptor electron pair donor

  15. 9.3 Acid-Base Reactions Strong Acids and Bases BrønstedAcids and Bases Acid-Base Neutralization Acids can be either strong or weak. A strong acid is a strong electrolyte. weak

  16. Acid-Base Reactions A weak acid is a weak electrolyte; it does not dissociate completely. Acetic acid, HC2H3O2, is an example. Most acids are weak acids. H+(aq) + C2H3O2(aq) HC2H3O2(l) – acidic proton

  17. Neutralization Reactions Acid + Base → salt (ionic compound) + water HCl + NaOH → NaCl + H2O Write the neutralization reaction for any two other strong acid base pairs. Strong Bases - LiOH, NaOH, KOH, or Ca(OH)2. Strong Acids – HClO4, H2SO4, HI, HBr, HCl, HNO3. What salt is formed form the reaction of nitric acid with calcium hydroxide? a) CaNO3 b) Ca2NO3 c) Ca(NO3)2 d) CaNO2 2 HNO3 + Ca(OH)2 → Ca(NO3)2 + 2 H2O

  18. Acid-Base Titrations Quantitative studies of acid-base neutralization reactions are most conveniently carried out using a technique known as a titration. The point in the titration where the acid has been neutralized is called the equivalence point. The color change is brought about by the use of an indicator. Indicators have distinctly different colors in acidic and basic media. The indicator is chosen so that the color change, or endpoint, is very close to the equivalence point. Phenolphthalein is a common indicator.

  19. Strong Acids HCl, HBr, HI, HNO3, HCLO3, HClO4, H2SO4 HCl(aq) → H+(aq) + Cl-(aq) 100% dissociated All other acids are weak: Some examples include …. HF hydrofluoric acid HCN hydrocyanic acid CH3COOH acetic acid H2CO3 carbonic acid (or CO2 + H2O) H3PO4 phosphoric acid HF(aq) ↔ H+(aq) + F-(aq) partially dissociated

  20. Neutralization Reactions Acid + Base → salt (ionic compound) + water HCl + NaOH → NaCl + H2O Write the neutralization reaction for any two other strong acid base pairs. Strong Bases - LiOH, NaOH, KOH, or Ca(OH)2. Strong Acids – HClO4, H2SO4, HI, HBr, HCl, HNO3. What salt is formed form the reaction of nitric acid with barium hydroxide? a) BaNO3 b) Ba2NO3 c) Ba(NO3)2 d) BaNO2 2 HNO3 + Ca(OH)2 → Ca(NO3)2 + 2 H2O 2 HNO3(aq)+ Ba(OH)2(aq) → Ba(NO3)2(aq)+ 2 H2O(ℓ) Is it soluble? a) yes b) no Net ionic equation ….. 2 H+(aq)+ 2OH-(aq) → 2 H2O(ℓ)

  21. Acid-Base Titrations Quantitative studies of acid-base neutralization reactions are most conveniently carried out using a technique known as a titration. The point in the titration where the acid has been neutralized is called the equivalence point. The color change is brought about by the use of an indicator. Indicators have distinctly different colors in acidic and basic media. The indicator is chosen so that the color change, or endpoint, is very close to the equivalence point. Phenolphthalein is a common indicator.

  22. 1. Balanced reaction 2. moles known 3. moles unknown 4. amount unknown 2 HNO3(aq)+ Ba(OH)2(aq) → Ba(NO3)2(aq)+ 2 H2O(ℓ) What volume of 6.0 M nitric acid is required to reach the equivalence point in a titration with 250. ml of 0.47 M Barium hydroxide? a) 20 ml b) 39 ml c) 52 ml d) 78 ml Given: 6.0M 0.47 M 250. ml 2 HNO3(aq)+ Ba(OH)2(aq) → Ba(NO3)2(aq)+ 2 H2O(ℓ) Moles known:0.250 L • 0.47 moles = 0.118 moles 1 L Moles unknown:2 moles HNO3 • 0.118 moles Ba(OH)2 = 0.236 moles HNO3 1 mole Ba(OH)2 amount unknown:0.236 moles HNO3 • 1 L HNO3= 0.039 L or 39 ml 6.0 moles What is the [Ba(OH)2] if 27.3 ml of 6.00 M HNO3 is required to titrate 100.0 ml of an unknown Barium hydroxide solution? a) 0.205M b) 0.410M c) 0.819 M d) 1.64 M

  23. Oxidation Reduction Reactions -(Redox) Transfer of electrons (between atoms in compounds) oxidation = loss of electrons reduction = gain of electrons oxidizing agent –gets reduced by accepting electrons reducing agent – gets oxidized by donating electrons You can’t have one without the other A reaction is considered an oxidation-reduction reaction if any element in the reaction changes its ‘oxidation state’ during the reaction. example ….. Cu2+(aq) + Zn(s) Zn2+(aq) + Cu(s)

  24. Oxidation-Reduction Reactions Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)

  25. Oxidation State - Rules 1. 0 in elemental form (e.g. H2, O2, Zn(s)) 2. Ion charge = oxidation state for ions (of elements) 3. O = -2 (except in peroxides, e.g. H2O2) 4. H = +1 (except as hydride in ionic cpd) 5. F = -1 (other halides = -1 if ionic cpd) 6. Sum of ox #s = charge of ion or 0 for neutral cpd +4 -4 -4 -6 +4 +6 +4 -4 -3 -2 +1 +1 CH4 C2H6 CO2

  26. Oxidation State - Rules 1. 0 in elemental form (e.g. H2, O2, Zn(s)) 2. Ion charge = oxidation state for ions (of elements) 3. O = -2 (except in peroxides, e.g. H2O2) 4. H = +1 (except as hydride in ionic cpd) 5. F = -1 (other halides = -1 if ionic cpd) 6. Sum of ox #s = charge of ion or 0 for neutral cpd Mn is ….. a) +1 b) +2 c) +6 d) +7 KMnO4 K2Cr2O7 Cr is ….. a) +1 b) +2 c) +6 d) +7 Cl is ….. a) -1 b) +3 c) +7 d) +8 ClO4- C2H6O C is ….. a) -4 b) -2 c) +2 d) +4 S is ….. a) +1 b) +2 c) +6 d) +7 SO42-

  27. +1 0 0 +2 Oxidation-Reduction Reactions In a ‘redox’ reaction the oxidation state of 2 elements will change. One will increase (get oxidized) … and the other will decrease (get reduced). Reaction of acid with metals …. 2HCl(aq) + Zn(s) ZnCl2(aq) + H2(g) Half reactions: write one reaction showing species reduced (e- is reactant) …. And another reaction showing species oxidized (e- is product) oxidation: Zn→ Zn2+ + 2e-Zn is oxidized and is the reducing agent reduction: 2H+ + 2e-→ H2H is reduced and HCl (or H+) is the oxidizing agent

  28. Oxidation-Reduction Reactions Any combustion reaction: (CHO) + O2 CO2 + H2O 1 CH4 + 2 O2  1 CO2 + 2 H2O -4 +1 0 +4 -2 +1 -2 Oxidation: CH4+ 2 H2O → CO2 + 8e- + 8H+ Reduction: O2+ 4e- + 4H+→ 2 H2O Oxygen is reduced and O2 is the oxidizing agent Carbon is oxidized and methane is the reducing agent

  29. Breath Analyzer -2 +6 3 C2H6O + 2 K2Cr2O7(aq)+ 8 H2SO4(aq) 3 C2H4O2+ 2 Cr2(SO4)3(aq)+ 2 K2SO4(aq)+ 11 H2O 0 +3 Reduction: Cr2O72-(aq) 2 Cr3+ 14H+ + 6e- + + 7H2O + 7H2O Reduction: Cr2O72-(aq) 2 Cr3+ 14H+ + 6e- + Oxidation: C2H6O C2H4O2 H2O + +4e- + 4H+ C is oxidized and ethanol is the reducing agent Cr is reduced and the chromate ion is the oxidizing agent

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