Chapter 4 Handouts

Chapter 4 Handouts - Chapter 4 Chemical Quantities and...

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Unformatted text preview: Chapter 4 Chemical Quantities and Aqueous Reactions Quantities in Chemical Reactions 1.  Write balanced chemical equation 2.  Convert quantities of known substances into moles 3.  4.  Convert moles of sought quantity into desired units Reaction Stoichiometry •  The coefficients in a balanced chemical equation specify the relative amounts in moles of each of the substances involved in the reaction 2 C8H18(l) + 25 O2(g) ! 16 CO2(g) + 18 H2O(g) 2 moles of C8H18 react with 25 moles of O2 to form 16 moles of CO2 and 18 moles of H2O Predicting Amounts from Stoichiometry •  The amounts of any other substance in a •  chemical reaction can be determined from the amount of just one substance How much CO2 can be made from 22.0 moles of C8H18 in the combustion of C8H18? 2 C8H18(l) + 25 O2(g) ! 16 CO2(g) + 18 H2O(g) Practice - How many moles of water are made in the combustion of 0.10 moles of glucose? C6H12O6 + 6 O2 ! 6 CO2 + 6 H2O Given: Find: Conceptual Plan: Relationships: Solution: Check: Mass (g) of Compound A Mass (g) of Compound B Use molar mass of Compound A Moles of Compound A Use mole ratios of A and B from balanced equation Use molar mass of Compound B Moles of Compound B Example 4.1: How many grams of glucose can be synthesized from 37.8 g of CO2 in photosynthesis? Given: Find: Conceptual Plan: Relationships: Solution: Check: The Limiting Reactant (6) (12) Limiting Reagent Limiting and Excess Reactants in the Combustion of Methane CH4(g) + 2 O2(g) ! CO2(g) + 2 H2O(g) •  If we have 5 mols of CH4 and 8 mols of O2, which is the limiting reactant? Practice — How many moles of Si3N4 can be made from 1.20 moles of Si and 1.00 moles of N2 in the reaction 3 Si + 2 N2 ! Si3N4? Given: Find: Conceptual Plan: Relationships: Solution: Reaction Yield Theoretical Yield Actual Yield is the amount of product actually obtained from a reaction. Let’s do one together…. Titanium is a strong, lightweight, corrosion-resistant metal that is used in rockets, aircrafts, jet engines, and bicycle frames. It is prepared by the reaction of titanium (IV) chloride with molten magnesium at high temperatures: TiCl4 + 2Mg ! Ti + 2MgCl2 In a certain industrial operation, 3.54 x 107 g of TiCl4 are reacted with 1.13 x 107 g of Mg. Calculate the percent yield of Ti if 7.91 x 106 g of Ti are produced. Solutions A solution is a homogenous mixture of 2 or more substances regardless of state The solute is(are) the substance(s) present in the what is dissolved smaller amount(s) The solvent is the substance present in the larger does the dissolving amount Solution Solvent Solute Solution Concentration •  Qualitatively, solutions are •  •  often described as dilute or concentrated Dilute solutions have a small amount of solute compared to solvent Concentrated solutions have a large amount of solute compared to solvent Concentration = amount of solute in a given amount of solution Solution Concentration: Molarity molarity, M = amount of solute (in moles) / amount of solution (in L) What mass of KI is required to make 500 mL of a 2.80 M KI solution? volume KI moles KI grams KI ***always start with the given information that has 1 unit 500 ml x (1L/1000mL) x (2.8 mol KI/1 L soln) x (166g KI/1mol KI) = 232g KI Example 4.5: Find the molarity of a solution that has 25.5 g KBr dissolved in 1.75 L of solution Given: Find: Conceptual Plan: 25.5g KBr, 1/75 L solution molarity, M g KBr x (mol KBr/L sol'n) = M Relationships: Solution: 25.5 g KBr x (1mol KBr/119.00g KBr) = .21429 mol KBr (.21429 mol/ 1.75 L) = .12245 L solution Check: Example 4.6: How many liters of 0.125 M NaOH contain 0.255 mol NaOH? Given: Find: Conceptual Plan: moles to L Relationships: Solution: Check: 0.255 mol NaOH x (1L solution/0.125 mol NaOH) = 2.04 L solution Dilution Dilution is the procedure for preparing a less concentrated solution from a more concentrated solution Dilution Add Solvent Moles of solute before dilution (1) = M1 x V1 = M2 x V2 Moles of solute after dilution (2) Example 4.7: To what volume should you dilute 0.200 L of 15.0 M NaOH to make 3.00 M NaOH? Given: Find: Conceptual Plan: Relationships: Solution: Check: [(15.0 mol/L) x (.200L)] / (3.00 mol/L) = 1.00L Practice – What is the concentration of a solution prepared by diluting 45.0 mL of 8.25 M HNO3 to 135.0 mL? Given: Find: Conceptual Plan: Relationships: Solution: Check: [(8.25 mol/L) x (45.0mL)] / (135.0 mL) = 2.75mol/L = 2.75M Practice – How would you prepare 200.0 mL of 0.25 M NaCl solution from a 2.0 M solution? Given: Find: Conceptual Plan: Relationships: Solution: [(.25 mol/L) x (200.0mL)] / (2.00 mol/L) = 25mL so you've added 175mL of water Check: Solution Stoichiometry •  Because molarity relates the moles of solute to the liters of solution, it can be used to convert between amount of reactants and/or products in a chemical reaction Example 4.8: What volume of 0.150 M KCl is required to completely react with 0.150 L of 0.175 M Pb(NO3)2 in the reaction 2 KCl(aq) + Pb(NO3)2(aq) ! PbCl2(s) + 2 KNO3(aq)? Given: Find: Conceptual Plan: Relationships: Solution: Check: .150 L Pb (NO3)2 x (1.75 mol/ 1 L) x (2 mol/ 1 mol) x ( 1 L/ .150 mol) = .350 L KCl What Happens When a Solute Dissolves? •  There are attractive forces between the solute particles holding them together •  there are also attractive forces between the colvent molecules •  When we mix the solute with the solvent, there are attractive forces between the solute particles and the solvent molecules •  if the attractions between solute and solvent are strong enough, the solute will dissolve for dissolution to occure solute-solvent interactions must be stronger than solute-solute and solvent-solute interactions (might be written wrong) Electrolytes and Nonelectrolytes •  Materials that dissolve •  in water to form a solution that will conduct electricity are called electrolytes Materials that dissolve in water to form a solution that will not conduct electricity are called nonelectrolytes Salt vs. Sugar Dissolved in Water ionic compounds dissociate into ions when they dissolve ELECTROLYTE molecular compounds do not dissociate when they dissolve NON-ELECTROLYTE Conduct electricity in solution? Cations (+) and Anions (-) Strong Electrolyte – 100% dissociation NaCl (s) H 2O Na+ (aq) + Cl- (aq) Weak Electrolyte – not completely dissociated CH3COOH CH3COO- (aq) + H+ (aq) A reversible reaction. The reaction can occur in both directions Hydration + "-# O : slightly negative H 2O "+# - H : slightly positive ***************************** ************ Solubility Rules ************************* ************ know this chart Practice – Determine if each of the following is soluble in water KOH AgBr CaCl2 Pb(NO3)2 PbSO4 anything with K is soluble no yes yes, becasue of Nitrate no, it is an exception 2 KI(aq) + Pb(NO3)2(aq) ! PbI2(s) + 2 KNO3(aq) •  Precipitation reactions are reactions in which a solid forms when we mix two solutions No Precipitate Formation = No Reaction KI(aq) + NaCl(aq) ! KCl(aq) + NaI(aq) all ions still present, $ no reaction no reaction Ionic Equations •  Equations that describe the chemicals put into the water and the product molecules are called molecular equations •  Equations that describe the material’s structure when dissolved are called complete ionic equations " aqueous strong electrolytes are written as ions # soluble salts, strong acids, strong bases " insoluble substances, weak electrolytes, and nonelectrolytes are written in molecule form # solids, liquids, and gases are not dissolved, therefore molecule form Ionic Equations •  Ions that are both reactants and products are called spectator ions $  An ionic equation in which the spectator ions are removed is called a net ionic equation Example 4.10: Write the equation for the precipitation reaction between an aqueous solution of potassium carbonate and an aqueous solution of nickel(II) chloride 1. Write the formulas of the reactants 2. Determine the possible products a) determine the ions present b) exchange the Ions c) write the formulas of the products #  balance charges Acids Have a sour taste. Vinegar owes its taste to acetic acid. Citrus fruits contain citric acid. Cause color changes in plant dyes. React with certain metals to produce hydrogen gas. 2HCl (aq) + Mg (s) MgCl2 (aq) + H2 (g) React with carbonates and bicarbonates to produce carbon dioxide gas 2HCl (aq) + CaCO3 (s) CaCl2 (aq) + CO2 (g) + H2O (l) Aqueous acid solutions conduct electricity. Bases Have a bitter taste. Feel slippery. Many soaps contain bases. Cause color changes in plant dyes opposite that of acids. Aqueous base solutions conduct electricity. 4.3 Arrhenius acid Arrhenius base NaOH is a substance that produces H+(H3O+) in water is a substance that produces OH- in water Na+ + OH- Hydronium ion, hydrated proton, H3O+ Electron rich region electron poor region A Brønsted acid A Brønsted base base acid is a ptoton donor is a proton acid base A Brønsted acid must contain at least one ionizable proton! Strong Acids Hydrochloric acid Hydrobromic acid Hydroiodic acid Nitric acid Sulfuric acid Perchloric acid HCl HBr HI HNO3 H2SO4 HClO4 completly dissociate Weak Acids Hydrofluoric acid Nitrous acid Phosphoric acid Acetic acid Bases HF HNO2 H3PO4 CH3COOH reversible reactoins Monoprotic acids HCl H+ + Cl- HNO3 H+ + NO3- CH3COOH H+ + CH3COO- Diprotic acids H2SO4 H+ + HSO4- HSO4- H+ + SO42- Triprotic acids H3PO4 H2PO4HPO42- H+ + H2PO4H+ + HPO42H+ + PO43- strong electrolyte Identify each of the following species as a Brønsted acid, base. (a) HI, (b) CH3COO-. HI (aq) H+ (aq) + Br- (aq) CH3COO- (aq) + H+ (aq) Bronsted CH3COOH (aq) bronsted base 4.3 Neutralization Reaction acid + base HCl (aq) + NaOH (aq) H+ + Cl- + Na+ + OHH+ + OH- salt + water NaCl (aq) + H2O Na+ + Cl- + H2O H 2O H2SO4 (aq) + 2NaOH (aq) Na2SO4 (aq) + 2H2O 2H+ + SO42- + 2Na+ + 2OH- 2Na+ + SO42- + 2H2O H+ + OH- H 2O 4.3 Practice – Predict the products and balance the equation HCl(aq) + Ba(OH)2(aq) ! H2SO4(aq) + Sr(OH)2(aq) !# Acid-Base Titrations In a titration a solution of accurately known concentration is added gradually added to another solution of unknown concentration until the chemical reaction between the two solutions is complete. Equivalence point – the point at which the reastoin is complete Indicator – Slowly add base to unknown acid UNTIL the indicator changes color Titration What volume of a 1.420 M NaOH solution is Required to titrate 25.00 mL of a 4.50 M H2SO4 solution? WRITE THE CHEMICAL EQUATION! H2SO4 + 2NaOH 2H2O + Na2SO4 Let’s do one more… What volume of a 1.420 M NaOH solution is required to titrate 25.00 mL of a 1.500 M H3PO4 solution? Practice — What is the concentration of NaOH solution that requires 27.5 mL to titrate 50.0 mL of 0.1015 M H2SO4? 2 NaOH(aq) + H2SO4(aq) ! Na2SO4(aq) + 2 H2O(aq) Given: Find: Conceptual Plan: Relationships: Solution: Check: Other Patterns in Reactions •  The precipitation and acid-basereactions all involve exchanging the ions in the solution •  redox reactions " also known as " many involve the reaction of a substance with O2(g) 4 Fe(s) + 3 O2(g) ! 2 Fe2O3(s) Redox Reactions (electron transfer reactions) 2Mg (s) + O2 (g) 2Mg O2 + 4e- 2Mg2+ + 4e2O2- 2MgO (s) oxidation half reaction (lose e-) reductino half-reaction (gain e-) 2Mg + O2 + 4e2Mg + O2 2Mg2+ + 2O2- + 4e2MgO Zn0 C u0 CuSO4 AgNO3 Metal Displacement Reaction Zn (s) + CuSO4 (aq) Zn ZnSO4 (aq) + Cu (s) Zn2+ + 2e- Zn is oxidized Cu2+ + 2e- Cu Cu2+ is reduced Z n is the reducing agent Cu2+ is the oxidizing agent LEO the lion goes GER! (lose electron oxidized) (Gain Elections Reduced) Copper wire reacts with silver nitrate to form silver metal. What is the oxidizing agent in the reaction? Oxidation number The charge the atom would have in a molecule (or an ionic compound) if electrons were completely transferred. 1.  Free elements (uncombined state) have an oxidation number of zero. Na, Be, K, Pb, H2, O2, P4 = 0 2.  In monatomic ions, the oxidation number is equal to the charge on the ion. Li+, Li = +1; Fe 3+, Fe = +3 3.  The oxidation number of oxygen is usually –2. In H2O2 and O22- it is –1. 4.  The oxidation number of hydrogen is +1 except when it is bonded to metals in binary compounds. In these cases, its oxidation number is –1 (LiAlH4). 6. The sum of the oxidation numbers of all the atoms in a molecule or ion is equal to the charge on the molecule or ion. Figure 4.10 The oxidation numbers of elements in their compounds Practice – Assign an oxidation state to each element in the following •  Br2 Br = 0 •  K+ K= +1 •  LiF Li= +1 & F= -1 •  CO2 0=-2, C= +4 •  SO42! 0=-2, S= +6 •  Na2O2 Oxidation and Reduction Another Definition •  Oxidation occurs when an atom’s oxidation •  state increases during a reaction Reduction occurs when an atom’s oxidation state decreases during a reaction Practice – Assign oxidation states, determine the element oxidized and reduced, and determine the oxidizing agent and reducing agent in the following reactions: ...
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This note was uploaded on 02/01/2012 for the course CHEM 105 taught by Professor Woodrum during the Fall '08 term at Kentucky.

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