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1 3-1 Chapter 3 Stoichiometry of Formulas and Equations

2 3-2 Mole - Mass Relationships in Chemical Systems 3.1 The Mole 3.2 Determining the Formula of an Unknown Compound 3.3 Writing and Balancing Chemical Equations 3.4 Calculating the Amounts of Reactant and Product 3.5 Fundamentals of Solution Stoichiometry

3 mole(mol) - the amount of a substance that contains the same number of entities as there are atoms in exactly 12 g of carbon-12. This amount is 6.022x1023. The number is called Avogadro s number and is abbreviated as N. One mole (1 mol) contains 6.022x1023 entities (to four significant figures) 3-3

12 red marbles @ 7g each = 84g 12 yellow

4 3-4 Figure 3.1 Counting objects of fixed relative mass. 12 red 7g each = 84g 12 yellow each = 48g 55.85g Fe = x atoms Fe 32.07g S = x atoms S

Figure 3.2 One mole of common substances. Oxygen 32.

5 Figure 3.2 One mole of common substances. Oxygen g CaCO g Water g 3-5 Copper g

6 3-6 Information Contained in the Chemical Formula of Glucose C 6 H 12 O 6 ( M = g/mol) Table 3.1 Carbon (C) Hydrogen (H) Oxygen (O) Atoms/molecule of compound 6 atoms 12 atoms 6 atoms Moles of atoms/ mole of compound 6 moles of atoms 12 moles of atoms 6 moles of atoms Atoms/mole of compound 6(6.022 x ) atoms 12(6.022 x ) atoms 6(6.022 x ) atoms Mass/molecule of compound 6(12.01 amu) =72.06 amu 12(1.008 amu) =12.10 amu 6(16.00 amu) =96.00 amu Mass/mole of compound g g g

7 3-7 Interconverting Moles, Mass, and Number of Chemical Entities Mass (g) = no. of moles x no. of grams 1 mol g No. of moles = mass (g) x 1 mol no. of grams M No. of entities = no. of moles x 6.022x1023 entities 1 mol No. of moles = no. of entities x 1 mol 6.022x10 23 entities

8 3-8 Figure 3.3 MASS(g) of element Summary of the mass-molenumber relationships for elements. M (g/mol) AMOUNT(mol) of element Avogadro s number (atoms/mol) ATOMS of element

9 3-9 Sample Problem 3.1 Calculating the Mass and the Number of Atoms in a Given Number of Moles of an Element PROBLEM: (a) Silver (Ag) is used in jewelry and tableware but no longer in U.S. coins. How many grams of Ag are in mol of Ag? (b) Iron (Fe), the main component of steel, is the most important metal in industrial society. How many Fe atoms are in 95.8g of Fe?

10 3-10 Figure 3.4 MASS(g) of compound Summary of the mass-molenumber relationships for compounds. AMOUNT(mol) of compound M (g/mol) chemical formula AMOUNT(mol) of elements in compound MOLECULES (or formula units) of compound Avogadro s number (molecules/mol)

11 3-11 Sample Problem 3.2 Calculating the Moles and Number of Formula Units in a Given Mass of a Compound PROBLEM: Ammonium carbonate is white solid that decomposes with warming. Among its many uses, it is a component of baking powder, first extinguishers, and smelling salts. How many formula unit are in 41.6 g of ammonium carbonate?

12 3-12 Mass percent from the chemical formula Mass % of element X = atoms of X in formula x atomic mass of X (amu) molecular (or formula) mass of compound(amu) x 100 Mass % of element X = moles of X in formula x molar mass of X (amu) molecular (or formula) mass of compound (amu) x 100

13 3-13 Sample Problem 3.3 Calculating the Mass Percents and Masses of Elements in a Sample of Compound PROBLEM: Glucose (C 6 H 12 O 6 ) is the most important nutrient in the living cell for generating chemical potential energy. (a) What is the mass percent of each element in glucose? (b) How many grams of carbon are in 16.55g of glucose?

14 3-14 Sample Problem 3.3 continued Calculating the Mass Percents and Masses of Elements in a Sample of Compound

15 3-15 Empirical and Molecular Formulas Empirical Formula - Molecular Formula -

16 3-16 Sample Problem 3.4 Determining the Empirical Formula from Masses of Elements PROBLEM: Elemental analysis of a sample of an ionic compound showed 2.82 g of Na, 4.35 g of Cl, and 7.83 g of O. What are the empirical formula and name of the compound?

17 3-17 Sample Problem 3.5 Determining a Molecular Formula from Elemental Analysis and Molar Mass PROBLEM: During physical activity, lactic acid (M=90.08 g/mol) forms in muscle tissue and is responsible for muscle soreness. Elemental analysis shows that this compound contains 40.0 mass% C, 6.71 mass% H, and 53.3 mass% O. (a) Determine the empirical formula of lactic acid. (b) Determine the molecular formula.

18 3-18 Sample Problem 3.5 continued Determining a Molecular Formula from Elemental Analysis and Molar Mass

19 3-19 Figure 3.5 Combustion apparatus for determining formulas of organic compounds. m m C n H m + (n+ ) O 2 = n CO(g) + H 2 O(g) 2 2

20 3-20 Sample Problem 3.6 PROBLEM: Determining a Molecular Formula from Combustion Analysis Vitamin C (M=176.12g/mol) is a compound of C,H, and O found in many natural sources especially citrus fruits. When a g sample of vitamin C is placed in a combustion chamber and burned, the following data are obtained: mass of CO 2 absorber after combustion mass of CO 2 absorber before combustion mass of H 2 O absorber after combustion mass of H 2 O absorber before combustion What is the molecular formula of vitamin C? =85.35g =83.85g =37.96g =37.55g

21 3-21 Sample Problem 3.6 continued Determining a Molecular Formula from Combustion Analysis

22 3-22 Table 3.2 Constitutional Isomers of C 2 H 6 O Property Ethanol Dimethyl Ether M(g/mol) Boiling Point Density at 20 0 C C g/ml (liquid) C g/ml (gas) Structural formulas H H C H H C H H OH H C O H H C H H Space-filling models

23 3-23 Figure 3.6 The formation of HF gas on the macroscopic and molecular levels.

24 3-24 Figure 3.7 A three-level view of the chemical reaction in a flashbulb.

25 translate the statement balance the atoms adjust the coefficients check the atom balance specify states of matter 3-25

26 3-26 Sample Problem 3.7 Balancing Chemical Equations PROBLEM: Within the cylinders of a car s engine, the hydrocarbon octane (C 8 H 18 ), one of many components of gasoline, mixes with oxygen from the air and burns to form carbon dioxide and water vapor. Write a balanced equation for this reaction.

27 Figure 3.8 Summary of the mass-mole-number relationships in a chemical reaction. MASS(g) of compound A MASS(g) of compound B M (g/mol) of compound A M (g/mol) of compound B AMOUNT(mol) of compound A molar ratio from AMOUNT(mol) of compound B MOLECULES (or formula units) of compound A balanced equation Avogadro s number (molecules/mol) MOLECULES (or formula units) of compound B Avogadro s number (molecules/mol) 3-27

28 3-28 Sample Problem 3.8 Calculating Amounts of Reactants and Products PROBLEM: In a lifetime, the average American uses 1750 lb(794 g) of copper in coins, plumbing, and wiring. Copper is obtained from sulfide ores, such as chalcocite, or copper(i) sulfide, by a multistep process. After an initial grinding, the first step is to roast the ore (heat it strongly with oxygen gas) to form powdered copper(i) oxide and gaseous sulfur dioxide. (a) How many moles of oxygen are required to roast 10.0 mol of copper(i) sulfide? (b) How many grams of sulfur dioxide are formed when 10.0 mol of copper(i) sulfide is roasted? (c) How many kilograms of oxygen are required to form 2.86 kg of copper(i) oxide?

29 3-29 Sample Problem 3.8 Calculating Amounts of Reactants and Products

molecule C 3 H 8 + 5 molecules O 2 Products 3CO 2 (g) + 4H 2 O(g) 3 molecules CO 2 + 4 molecules H 2 O amount (mol) 1

30 3-30 Table 3.3 Information Contained in a Balanced Equation Viewed in Terms of molecules Reactants C 3 H 8 (g) + 5O 2 (g) 1 molecule C 3 H molecules O 2 Products 3CO 2 (g) + 4H 2 O(g) 3 molecules CO molecules H 2 O amount (mol) 1 mol C 3 H mol O 2 3 mol CO mol H 2 O mass (amu) amu C 3 H amu O amu CO amu H 2 O mass (g) g C 3 H g O g CO g H 2 O total mass (g) g g

31 3-31 Sample Problem 3.9 Using Molecular Depictions to Solve a Limiting- Reactant Problem PROBLEM: Nuclear engineers use chlorine trifluoride in the processing of uranium fuel for power plants. This extremely reactive substance is formed as a gas in special metal containers by the reaction of elemental chlorine and fluorine. (a) Suppose the box shown at left represents a container of the reactant mixture before the reaction occurs (with chlorine colored green). Name the limiting reactant, and draw the container contents after the reaction is complete. (b) When the reaction is run again with mol of Cl 2 and 3.00 mol of F 2, what mass of chlorine trifluoride will be prepared?

32 3-32 Sample Problem 3.9 continued Using Molecular Depictions to Solve a Limiting- Reactant Problem

33 3-33 Sample Problem 3.10 Calculating Amounts of Reactant and Product in a Limiting-Reactant Problem PROBLEM: A fuel mixture used in the early days of rocketry is composed of two liquids, hydrazine(n 2 H 4 ) and dinitrogen tetraoxide(n 2 O 4 ), which ignite on contact to form nitrogen gas and water vapor. How many grams of nitrogen gas form when 1.00x10 2 g of N 2 H 4 and 2.00x10 2 g of N 2 O 4 are mixed?

34 3-34 Sample Problem 3.10 continued Calculating Amounts of Reactant and Product in a Limiting-Reactant Problem

35 3-35 Figure 3.9 The effect of side reactions on yield. A + B (reactants) C (main product) D (side products)

36 3-36 Sample Problem 3.11 Calculating Percent Yield PROBLEM: Silicon carbide (SiC) is an important ceramic material that is made by allowing sand(silicon dioxide, SiO2) to react with powdered carbon at high temperature. Carbon monoxide is also formed. When kg of sand is processed, 51.4 kg of SiC is recovered. What is the percent yield of SiC from this process?

37 3-37 Sample Problem 3.12 Calculating the Molarity of a Solution PROBLEM: Glycine (H 2 NCH 2 COOH) is the simplest amino acid. What is the molarity of an aqueous solution that contains mol of glycine in 495 ml?

38 3-38 Figure 3.10 Summary of mass-mole-number-volume relationships in solution. MASS (g) of compound in solution M (g/mol) AMOUNT (mol) of compound in solution Avogadro s number (molecules/mol) MOLECULES (or formula units) of compound in solution M (g/mol) VOLUME (L) of solution

39 3-39 Sample Problem 3.13 Calculating Mass of Solute in a Given Volume PROBLEM: of Solution A buffered solution maintains acidity as a reaction occurs. In living cells phosphate ions play a key buffering role, so biochemistry often study reactions in such solutions. How many grams of solute are in 1.75 L of M sodium monohydrogen phosphate?

40 3-40 Figure 3.11 Converting a concentrated solution to a dilute solution.

41 3-41 Sample Problem 3.14 Preparing a Dilute Solution from a Concentrated Solution PROBLEM: Isotonic saline is a 0.15 M aqueous solution of NaCl that simulates the total concentration of ions found in many cellular fluids. Its uses range from a cleaning rinse for contact lenses to a washing medium for red blood cells. How would you prepare 0.80 L of isotomic saline from a 6.0 M stock solution?

42 3-42 Sample Problem 3.15 Calculating Amounts of Reactants and Products for a Reaction in Solution PROBLEM: Specialized cells in the stomach release HCl to aid digestion. If they release too much, the excess can be neutralized with antacids. A common antacid contains magnesium hydroxide, which reacts with the acid to form water and magnesium chloride solution. As a government chemist testing commercial antacids, you use 0.10M HCl to simulate the acid concentration in the stomach. How many liters of stomach acid react with a tablet containing 0.10g of magnesium hydroxide?

43 3-43 Sample Problem 3.15 continued Calculating Amounts of Reactants and Products for a Reaction in Solution

44 3-44 Sample Problem 3.16 Solving Limiting-Reactant Problems for Reactions in Solution PROBLEM: Mercury and its compounds have many uses, from fillings for teeth (as an alloy with silver, copper, and tin) to the industrial production of chlorine. Because of their toxicity, however, soluble mercury compounds, such mercury(ii) nitrate, must be removed from industrial wastewater. One removal method reacts the wastewater with sodium sulfide solution to produce solid mercury(ii) sulfide and sodium nitrate solution. In a laboratory simulation, 0.050L of 0.010M mercury(ii) nitrate reacts with 0.020L of 0.10M sodium sulfide. How many grams of mercury(ii) sulfide form?

45 3-45 Sample Problem 3.16 continued Solving Limiting-Reactant Problems for Reactions in Solution

3. Formula and chemical reaction

Dr.ssa Rossana Galassi 320 4381420 rossana.galassi@unicam.it 3. Formula and chemical reaction Empirical formula Molecular formula Types of Chemical Formulas A chemical formula is comprised of element symbols