Chem 1A Dr. White Fall Handout 4

Transcription

1 Chem 1A Dr. White Fall Handout Types of Chemical Reactions (Overview) A. Non-Redox Rxns B. Oxidation-Reduction (Redox) reactions 4.6. Describing Chemical Reactions in Solution A. Molecular Equation B. Complete Ionic Equation

2 Chem 1A Dr. White Fall C. Net Ionic Equation 4.9. Oxidation-Reduction Reactions ( Redox Reactions ) A. Oxidation: B. Reduction: C. Oxidizing Agent: D. Reducing Agent:

3 Chem 1A Dr. White Fall E. Types of Redox Reactions 1. Combination (Composition) Metal + Oxygen Metal Oxide OR Nonmetal + Oxygen Nonmetal Oxide Example: Carbon + limited Oxygen and Carbon + excess Oxygen 2. Displacement a. Metal A + Metal B Salt Metal A Salt + Metal B Example: Magnesium + aqueous silver nitrate

4 Chem 1A Dr. White Fall b. Active Halogen + Metal Halogen Salt Less Active Halogen + Metal Halogen Salt Example: Fluorine + Aqueous Sodium Chloride c. Metal + Acid Metal salt + hydrogen gas Example: Aluminum + Hydrochloric acid d. Metal + Water Metal hydroxide + hydrogen gas Example: Lithium + Water

5 Chem 1A Dr. White Fall Combustion reactions with oxygen one common type: Hydrocarbon + Oxygen CO 2 (g) + H 2 O (l or g) Example: C 4 H 10 (g) + oxygen F. Oxidation Numbers

6 Chem 1A Dr. White Fall Lecture Examples: a. What is the oxidation state of chromium in Cr 2+? b. What is the oxidation state of chromium in CrCl 3? c. What is the oxidation state of chromium in the dichromate ion? M M + e - Oxidized: Loses electrons Oxidation # increases Reducing agent X X - Reduced: Gains electrons Oxidation # decreases Oxidizing agent Lecture Examples: In each of the following examples, determine has been oxidized and what has been reduced and which is the oxidizing agent and which is the reducing agent. a. Mg (s) + 2HCl (aq) MgCl 2 (aq) + H 2 (g) b. PbO (s) + CO (g) Pb (s) + CO 2 (g) c. sodium metal reacts with water.

7 Chem 1A Dr. White Fall Balancing Redox Reactions A. Balancing by Inspection 1. Lecture Example: Balance the following redox reaction: Zn (s) + Ag + (aq) Zn 2+ (aq) + Ag (s) B. Balancing by the Half Reaction Method 1. Balancing redox reactions that occurs in an acidic solution: Example: Cr 2 O NO - 2 Cr NO 3 Step 1: Split into half reactions Step 2: Balance atoms and charges in the half reactions (MOHE) M: balance miscellaneous atoms (atoms other than O and H) O: balance O by adding water molecules H: balance H by adding H + ions E: balance charges by adding electrons

8 Chem 1A Dr. White Fall Step 3: Multiply reactions by an integer so that the number of electrons are equal Step 4: Add half reactions together Step 5: Check that the atoms and charges are balanced 2. Balancing redox reactions that occurs in a basic solution: Example: MnO 4- (aq) + SO 3 2- (aq) MnO 2 (s) + SO 4 2- (aq) (basic) Follow steps 1-5:

9 Chem 1A Dr. White Fall Step 6: Note the number of H + ions in the equation, add this number of OH - ions to both sides Step 7: Simplify by noting that H + reacts with OH - to give H 2 O 3. Balance the following: Cr(OH) 3 (s) + ClO 3- ( aq) --> CrO 4 2- (aq) + Cl - (aq) (basic)

10 Chem 1A Dr. White Fall Precipitation Reactions A. Precipitation Reactions Overview Solubility rules 1. Salts containing Group I elements are soluble (Li +, Na +, K +, Cs +, Rb + ). Exceptions to this rule are rare. Salts containing the ammonium ion (NH 4 + ) are also soluble. 2. Salts containing nitrate ion (NO 3 - ) are generally soluble. 3. Salts containing Cl -, Br -, I - are generally soluble. Important exceptions to this rule are halide salts of Ag +, Pb 2+, and Hg Thus, AgCl, PbBr 2, and Hg 2 Cl 2 are all insoluble. 4. Most sulfate salts are soluble. Important exceptions to this rule include BaSO 4, PbSO 4, Ag 2 SO 4, Hg 2 SO 4 and CaSO Most hydroxide salts are only slightly soluble. Hydroxide salts of Group I elements are soluble. Hydroxide salts of Group II elements (Ca, Sr, and Ba) are slightly soluble. Hydroxide salts of transition metals and Al 3+ are insoluble. Thus, Fe(OH) 3, Al(OH) 3, Co(OH) 2 are not soluble. 6. Most sulfides, carbonates, chromates, and phosphates are only slightly soluble except for those containing alkali metals and NH 4 +.

11 Chem 1A Dr. White Fall Lecture Examples: a. Determine the net ionic equation for the following reaction: Ba(NO 3 ) 2 + Na 2 SO 4 BaSO 4 + 2NaNO 3 b. Write molecular and net ionic equations for the following: i. aqueous solutions of sodium chloride and iron (II) nitrate are mixed ii. Aqueous solutions of aluminum sulfate and sodium hydroxide are mixed 4.8 Acid-Base Reactions A. Acid-Base Definitions

12 Chem 1A Dr. White Fall B. Acid-Base reactions

13 Chem 1A Dr. White Fall Stoichiometric Calculations A. Mole to Mole Conversions Lecture Example: How many moles of hydrogen gas will form if mol of aluminum completely reacts with an excess of HCl? B. Gram to gram conversions Lecture Example: 96.1 g C 3 H 6 reacts with oxygen to form carbon dioxide and water. How much oxygen do we need to react with all the C 3 H 6? Lecture Example: Baking soda (NaHCO 3 ) is used as an antacid. It neutralizes HCl in the stomach. How many grams of HCl are neutralized per 1.00 gram of baking soda? If all the baking soda reacts, how many grams of water is produced?

14 Chem 1A Dr. White Fall Calculations involving Limiting Reactants A. Limiting reactants A simple example: Lecture Example: Carbon disulfide (CS 2 ) burns in oxygen according to the following equation. CS O 2 CO SO 2 Calculate the moles of SO 2 each component present in the flask at the end of the reaction when 3.0 mol of CS 2 and 3.0 mol of O 2 are mixed.

15 Chem 1A Dr. White Fall Lecture Example: Nitrogen gas is prepared by passing ammonia gas over solid copper (II) oxide at high temperatures. The other products are solid copper and water vapor. If 18.1 g of NH 3 are reacted with 90.4 g of CuO, which is the limiting reactant? How many grams of nitrogen gas will be formed? How much of the excess reactant is left? Lecture Example: For the reaction below, if you start with g Fe 2 O 3 and g CO, how many grams of Fe will you produce? Fe 2 O 3 (s) + 3 CO (g) 2 Fe (s) + 3 CO 2 (g)

16 Chem 1A Dr. White Fall B. Theoretical Yield C. Actual Yield D. Percentage Yield Lecture Example: if actual yield of Fe (s) produced from the previous example is 98.9 g, what is the percent yield? 4.7 Stoichiometry of Precipitation Reactions A. Lecture Examples: 1. How many grams of precipitate form when 35.0 ml of 0.160M barium chloride reacts with 58.0 ml of M sodium sulfate?

17 Chem 1A Dr. White Fall ml of 0.210M sodium sulfate reacts with L of 0.196M barium nitrate. A precipitate forms. What are the concentrations of all the ions after the reaction is complete? What is the mass of the ppt? Assume the volumes are additive.

18 Chem 1A Dr. White Fall L of 0.100M silver nitrate is mixed with L of 0.100M sodium carbonate. A precipitate forms. What are the concentrations of all the ions after the reaction is complete? What is the mass of the ppt? Assume the volumes are additive.

19 Chem 1A Dr. White Fall Titrations A. Types of Titration B. Equivalence Point C. Examples: 1. You perform an acid-base titration to standardize an HCl solution by placing ml in a flask with a few drops indicator solution. You put M NaOH in the buret with an initial buret reading of 0.55 ml. At the end point the reading on the buret is ml. What is the molarity of the acid solution?

20 Chem 1A Dr. White Fall What volume of M Ba(OH) 2 would neutralize ml of the HCl solution standardized in the preceding example. 3. A common analysis for iron is titration of iron (II) with potassium dichromate, K 2 Cr 2 O 7. The half reactions associated with this reaction are below: Cr 2 O H +1 +6e - 2Cr H 2 O Fe +2 Fe +3 + e - If a 5.00 ml sample of an unknown solution that contains iron (II) and iron (III) requires ml of M potassium dichromate to reach the equivalence point, calculate the concentration of Fe 2+ in the unknown solution.

21 Chem 1A Dr. White Fall Calcium ion is required for blood to clot and for many other cell processes. An abnormal calcium ion concentration is indicative of disease. To measure the calcium ion concentration, 1.00 ml of human blood is treated with a Na 2 C 2 O 4. The resulting precipitate is dissolved in dilute acid to release C 2 O 4 2- into solution and allow it to be oxidized using KMnO 4. This solution required 2.05 ml 4.88 x 10-4 M KMnO 4 to reach the endpoint of the titration. Calculate the molar concentration of calcium ion in the blood. NOTE: One product of the rxn is Mn 2+ and the other product of the redox reaction is a gas that turned limewater cloudy. 3.5 Percent Composition of Compounds A. Mass Percent from the Chemical Formula (not from data!)

22 Chem 1A Dr. White Fall Lecture Example: Consider magnesium chlorate. a. What is the mass % of each atom in magnesium chlorate? b. How many grams of oxygen are in g of magnesium chlorate? Lecture Example: A farmer determines that 60. Lbs N per acre is necessary in her field. If she is using ammonium nitrate as fertilizer, how many pounds of ammonium nitrate must she spread on 1.0 acre?

23 Chem 1A Dr. White Fall Determining the Formulas of Compounds A. Determining formulas from data: 1. Determining formulas from mass % (we did this already) Try this example on your own to review: During physical activity, lactic acid (molar mass = g/mol) forms in muscles and is responsible for muscle soreness. Elemental analysis shows that this compound contains 40.0 mass % C and 53.3 mass % O. Determine the empirical formula and the molecular formula for lactic acid. 2. Combustion analysis of organic compounds

24 Chem 1A Dr. White Fall Lecture Example: A g sample of an organic compound containing only carbon, hydrogen and oxygen was burned completely in air to produce g of CO 2 and g of H 2 O. What is the empirical formula of the compound? Chapter 5: Gases 5.2 The Gas Laws of Boyle, Charles, Avogadro A. Boyle's Law

25 Chem 1A Dr. White Fall B. Charles' Law C. Avogadro s Law

26 Chem 1A Dr. White Fall The Ideal Gas Law A. Derivation B. Examples using the ideal gas law: 1. Lecture Example: 2.96g Mercuric Chloride vaporized in a 1.0L bulb at 680 K and P=453 torr. What is the molar mass? 2. What is the density (in g/l) of CO 2 at 30.3 C and 744 mmhg?

27 Chem 1A Dr. White Fall A balloon contains 5.41 dm 3 of He at 24 C and kpa. The gas in the balloon is heated to 35 C and the pressure becomes kpa. What is the volume of the gas? (101.3 kpa = 1 atm) 5.4 Gas Stoichiometry A. Lecture Example: A sample of CH 4 (g) having a volume of 2.80 Liters at 25 C and 1.65 atm, was ignited with a sample of oxygen gas having a volume of 35.0 Liters at 31 C and 1.25 atm to produce CO 2 and H 2 O vapor. Calculate the volume of CO 2 formed at a pressure of 2.50 atm and a temperature of 125 C.

28 Chem 1A Dr. White Fall Copper dispersed in absorbent beds is used to react with oxygen impurities in ethylene used for producing polyethylene. The beds are regenerated when hot H 2 reduces the metal oxide forming the pure metal and H 2 O. On a laboratory scale, what volume of H 2 at 765 torr and 25 C is needed to reduce 35.5 g of copper (II) oxide? The Group IA metals react with the halogens (Group 7A) to form ionic metal halides. What mass of potassium chloride forms when 5.25 L of chlorine gas at atm and 293 K reacts with 17.0 g of potassium?