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© 2014 Pearson Education, Inc. Christian Madu, Ph.D. Collin College Lecture Presentation Chapter 3 Molecules, Compounds, and Chemical Equations.

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Presentation on theme: "© 2014 Pearson Education, Inc. Christian Madu, Ph.D. Collin College Lecture Presentation Chapter 3 Molecules, Compounds, and Chemical Equations."— Presentation transcript:

1 © 2014 Pearson Education, Inc. Christian Madu, Ph.D. Collin College Lecture Presentation Chapter 3 Molecules, Compounds, and Chemical Equations

2 © 2014 Pearson Education, Inc. How Many Different Substances Exist? Elements combine with each other to form compounds. The great diversity of substances that we find in nature is a direct result of the ability of elements to form compounds.

3 © 2014 Pearson Education, Inc. Hydrogen, Oxygen, and Water The dramatic difference between the elements hydrogen and oxygen and the compound water is typical of the differences between elements and the compounds that they form. When two or more elements combine to form a compound, an entirely new substance results.

4 © 2014 Pearson Education, Inc. Hydrogen, Oxygen, and Water

5 © 2014 Pearson Education, Inc. Definite Proportion A hydrogen–oxygen mixture can have any proportions of hydrogen and oxygen gas. Water, by contrast, is composed of water molecules that always contain two hydrogen atoms to every one oxygen atom. Water has a definite proportion of hydrogen to oxygen.

6 © 2014 Pearson Education, Inc. Definite Proportion

7 © 2014 Pearson Education, Inc. Chemical Bonds Compounds are composed of atoms held together by chemical bonds. Chemical bonds result from the attractions between the charged particles (the electrons and protons) that compose atoms. Chemical bonds are classified into two types: –Ionic –Covalent

8 © 2014 Pearson Education, Inc. Ionic Bonds Ionic bonds—which occur between metals and nonmetals—involve the transfer of electrons from one atom to another. When a metal interacts with a nonmetal, it can transfer one or more of its electrons to the nonmetal. –The metal atom then becomes a cation. –The nonmetal atom becomes an anion.

9 © 2014 Pearson Education, Inc. Ionic Bonds These oppositely charged ions attract one another by electrostatic forces and form an ionic bond. The result is an ionic compound, which in the solid phase is composed of a lattice— a regular three-dimensional array—of alternating cations and anions.

10 © 2014 Pearson Education, Inc. Ionic Bonds

11 © 2014 Pearson Education, Inc. Covalent Bonds Covalent bonds—which occur between two or more nonmetals—involve the sharing of electrons between two atoms. When a nonmetal bonds with another nonmetal, neither atom transfers its electron to the other. Instead the bonding atoms share some of their electrons. The covalently bound atoms compose a molecule. –Hence, we call covalently bonded compounds molecular compounds.

12 © 2014 Pearson Education, Inc. Representing Compounds: Chemical Formulas and Molecular Models A compound is represented with its chemical formula. Chemical formula indicates the elements present in the compound and the relative number of atoms or ions of each. –Water is represented as H 2 O. –Carbon dioxide is represented as CO 2. –Sodium Chloride is represented as NaCl. –Carbon tetrachloride is represented as CCl 4.

13 © 2014 Pearson Education, Inc. Types of Chemical Formulas Chemical formulas can generally be categorized into three different types: Empirical formula Molecular formula Structural formula

14 © 2014 Pearson Education, Inc. Types of Chemical Formulas An empirical formula gives the relative number of atoms of each element in a compound. A molecular formula gives the actual number of atoms of each element in a molecule of a compound. (a)For C 4 H 8, the greatest common factor is 4. The empirical formula is therefore CH 2. (b)For B 2 H 6, the greatest common factor is 2. The empirical formula is therefore BH 3. (c)For CCl 4, the only common factor is 1, so the empirical formula and the molecular formula are identical.

15 © 2014 Pearson Education, Inc. Types of Chemical Formulas A structural formula uses lines to represent covalent bonds and shows how atoms in a molecule are connected or bonded to each other. The structural formula for H 2 O 2 is shown below:

16 © 2014 Pearson Education, Inc. Types of Chemical Formulas The type of formula we use depends on how much we know about the compound and how much we want to communicate. A structural formula communicates the most information, while an empirical formula communicates the least.

17 © 2014 Pearson Education, Inc. A molecular model is a more accurate and complete way to specify a compound. A ball-and-stick molecular model represents atoms as balls and chemical bonds as sticks; how the two connect reflects a molecule’s shape. The balls are typically color- coded to specific elements. Molecular Models

18 © 2014 Pearson Education, Inc. Molecular Models In a space-filling molecular model, atoms fill the space between each other to more closely represent our best estimates for how a molecule might appear if scaled to visible size.

19 © 2014 Pearson Education, Inc. Ways of Representing a Compound

20 © 2014 Pearson Education, Inc. An Atomic-Level View of Elements and Compounds Elements may be either atomic or molecular. Compounds may be either molecular or ionic.

21 © 2014 Pearson Education, Inc. View of Elements and Compounds Atomic elements exist in nature with single atoms as their basic units. Most elements fall into this category. Examples are Na, Ne, C, K, Mg, etc. Molecular elements do not normally exist in nature with single atoms as their basic units; instead, they exist as molecules—two or more atoms of the element bonded together. There only seven diatomic elements and they are H 2, N 2, O 2, F 2, Cl 2, Br 2, and I 2. Also, P 4 and S 8 are polyatomic elements.

22 © 2014 Pearson Education, Inc. Molecular Elements

23 © 2014 Pearson Education, Inc. Molecular Compounds Molecular compounds are usually composed of two or more covalently bonded nonmetals. The basic units of molecular compounds are molecules composed of the constituent atoms. Water is composed of H 2 O molecules. Dry ice is composed of CO 2 molecules. Propane (often used as a fuel for grills) is composed of C 3 H 8 molecules.

24 © 2014 Pearson Education, Inc. Ionic Compounds Ionic compounds are composed of cations (usually a metal) and anions (usually one or more nonmetals) bound together by ionic bonds. The basic unit of an ionic compound is the formula unit, the smallest, electrically neutral collection of ions. The ionic compound table salt, with the formula unit NaCl, is composed of Na + and Cl – ions in a one-to-one ratio.

25 © 2014 Pearson Education, Inc. Molecular and Ionic Compounds

26 © 2014 Pearson Education, Inc. Polyatomic Ion Many common ionic compounds contain ions that are themselves composed of a group of covalently bonded atoms with an overall charge. This group of charged species is called polyatomic ions. –NaNO 3 contains Na + and NO 3 –. –CaCO 3 contains Ca 2+ and CO 3 2–. –KClO Contains K + and ClO –.

27 © 2014 Pearson Education, Inc. Ionic Compounds: Formulas and Names Summarizing Ionic Compound Formulas: –Ionic compounds always contain positive and negative ions. –In a chemical formula, the sum of the charges of the positive ions (cations) must equal the sum of the charges of the negative ions (anions). –The formula of an ionic compound reflects the smallest whole-number ratio of ions.

28 © 2014 Pearson Education, Inc. Ionic Compounds: Formulas and Names The charges of the representative elements can be predicted from their group numbers. The representative elements forms only one type of charge. Transition metals tend to form multiple types of charges. Hence, their charge cannot be predicted as in the case of most representative elements.

29 © 2014 Pearson Education, Inc. Naming Ionic Compounds Ionic compounds are usually composed of metals and nonmetals. Anytime you see a metal and one or more nonmetals together in a chemical formula, assume that you have an ionic compound. NaBr, Al 2 (CO 3 ) 3, CaHPO 4, and MgSO 4 are some examples of ionic compounds.

30 © 2014 Pearson Education, Inc. Ionic compounds can be categorized into two types, depending on the metal in the compound. The first type contains a metal whose charge is invariant from one compound to another. Whenever the metal in this first type of compound forms an ion, the ion always has the same charge. Naming Ionic Compounds

31 © 2014 Pearson Education, Inc. Naming Type I Ionic Compounds

32 © 2014 Pearson Education, Inc. Naming Type II Ionic Compounds The second type of ionic compound contains a metal with a charge that can differ in different compounds. The metals in this second type of ionic compound can form more than one kind of cation (depending on the compound). Its charge must therefore be specified for a given compound.

33 © 2014 Pearson Education, Inc. Type II Ionic Compounds Iron, for instance, forms a 2+ cation in some of its compounds and a 3+ cation in others. Metals of this type are often transition metals. –FeSO 4 Here iron is +2 cation (Fe 2+ ). –Fe 2 (SO 4 ) 3 Here iron is +3 cation (Fe 3+ ). –Cu 2 O Here copper is +1 cation (Cu + ). –CuO Here copper is +2 cation (Cu 2+ ). Some main group metals, such as Pb, Tl, and Sn, form more than one type of cation.

34 © 2014 Pearson Education, Inc. Type II Ionic Compounds

35 © 2014 Pearson Education, Inc. Naming Binary Ionic Compounds of Type I Cations Binary compounds contain only two different elements. The names of binary ionic compounds take the following form:

36 © 2014 Pearson Education, Inc. Naming Type I Binary Ionic Compounds For example, the name for KCl consists of the name of the cation, potassium, followed by the base name of the anion, chlor, with the ending -ide. KCl is potassium chloride. The name for CaO consists of the name of the cation, calcium, followed by the base name of the anion, ox, with the ending -ide. CaO is calcium oxide.

37 © 2014 Pearson Education, Inc. Base Names of Monoatomic Anions The base names of some nonmetals, and their most common charges in ionic compounds, are shown in Table 3.3.

38 © 2014 Pearson Education, Inc. Naming Type II Binary Ionic Compounds For these types of metals, the name of the cation is followed by a roman numeral (in parentheses) that indicates the charge of the metal in that particular compound. –For example, we distinguish between Fe 2+ and Fe 3+ as follows: Fe 2+ Iron(II) Fe 3+ Iron(III)

39 © 2014 Pearson Education, Inc. Naming Type II Binary Ionic Compounds The full names for compounds containing metals that form more than one kind of cation have the following form: The charge of the metal cation can be determined by inference from the sum of the charges of the nonmetal.

40 © 2014 Pearson Education, Inc. Naming Type II Binary Ionic Compounds For example, to name CrBr 3 determine the charge on the chromium. Total charge on cation + total anion charge = 0. Cr charge + 3(Br – charge) = 0. Since each Br has a –1 charge, then –Cr charge + 3(–1) = 0 –Cr charge –3 = 0 –Cr = +3 Hence, the cation Cr 3+ is called chromium(III), while Br – is called bromide. Therefore, CrBr 3 is chromium(III) bromide.

41 © 2014 Pearson Education, Inc. Type II Cation

42 © 2014 Pearson Education, Inc. Naming Ionic Compounds Containing Polyatomic Ions We name ionic compounds that contain a polyatomic ion in the same way as other ionic compounds, except that we use the name of the polyatomic ion whenever it occurs. For example, NaNO 2 is named according to –its cation, Na +, sodium, and –its polyatomic anion, NO 2 –, nitrite. Hence, NaNO 2 is sodium nitrite.

43 © 2014 Pearson Education, Inc. Common Polyatomic Ions

44 © 2014 Pearson Education, Inc. Oxyanions Most polyatomic ions are oxyanions, anions containing oxygen and another element. Notice that when a series of oxyanions contains different numbers of oxygen atoms, they are named according to the number of oxygen atoms in the ion. If there are two ions in the series, the one with more oxygen atoms has the ending -ate, and the one with fewer has the ending -ite. For example, NO 3 – is nitrateSO 4 2– is sulfate NO 2 – is nitriteSO 3 2– is sulfite

45 © 2014 Pearson Education, Inc. Oxyanions If there are more than two ions in the series then the prefixes hypo-, meaning less than, and per-, meaning more than, are used. ClO – hypochloriteBrO – hypobromite ClO 2 – chloriteBrO 2 – bromite ClO 3 – chlorateBrO 3 – bromate ClO 4 – perchlorateBrO 4 – perbromate

46 © 2014 Pearson Education, Inc. Hydrated Ionic Compounds Hydrates are ionic compounds containing a specific number of water molecules associated with each formula unit. –For example, the formula for epsom salts is MgSO 4 7H 2 O. –Its systematic name is magnesium sulfate heptahydrate. –CoCl 2 6H 2 O is cobalt(II)chloride hexahydrate.

47 © 2014 Pearson Education, Inc. Common hydrate prefixes hemi = ½ mono = 1 di = 2 tri = 3 tetra = 4 penta = 5 hexa = 6 hepta = 7 octa = 8 Other common hydrated ionic compounds and their names are as follows : –CaSO 4 1/2H 2 O is called calcium sulfate hemihydrate. –BaCl 2 6H 2 O is called barium chloride hexahydrate. –CuSO 4 6H 2 O is called copper sulfate hexahydrate. Hydrates

48 © 2014 Pearson Education, Inc. Molecular Compounds: Formulas and Names The formula for a molecular compound cannot readily be determined from its constituent elements because the same combination of elements may form many different molecular compounds, each with a different formula. –Nitrogen and oxygen form all of the following unique molecular compounds: NO, NO 2, N 2 O, N 2 O 3, N 2 O 4, and N 2 O 5.

49 © 2014 Pearson Education, Inc. Molecular Compounds Molecular compounds are composed of two or more nonmetals. Generally, write the name of the element with the smallest group number first. If the two elements lie in the same group, then write the element with the greatest row number first. –The prefixes given to each element indicate the number of atoms present.

50 © 2014 Pearson Education, Inc. Binary Molecular Compounds These prefixes are the same as those used in naming hydrates: mono = 1hexa = 6 di = 2hepta = 7 tri = 3octa = 8 tetra = 4nona = 9 penta = 5deca = 10 If there is only one atom of the first element in the formula, the prefix mono- is normally omitted.

51 © 2014 Pearson Education, Inc. Acids Acids are molecular compounds that release hydrogen ions (H + ) when dissolved in water. Acids are composed of hydrogen, usually written first in their formula, and one or more nonmetals, written second. –HCl is a molecular compound that, when dissolved in water, forms H + (aq) and Cl – (aq) ions, where aqueous (aq) means dissolved in water.

52 © 2014 Pearson Education, Inc. Acids Acids are molecular compounds that form H + when dissolved in water. –To indicate the compound is dissolved in water (aq) is written after the formula. »A compound is not considered an acid if it does not dissolve in water. Sour taste Dissolve many metals –such as Zn, Fe, Mg; but not Au, Ag, Pt Formula generally starts with H –e.g., HCl, H 2 SO 4

53 © 2014 Pearson Education, Inc. Binary acids have H +1 cation and nonmetal anion. Oxyacids have H + cation and polyatomic anion. Acids

54 © 2014 Pearson Education, Inc. Naming Binary Acids Write a hydro- prefix. Follow with the nonmetal name. Change ending on nonmetal name to –ic. Write the word acid at the end of the name.

55 © 2014 Pearson Education, Inc. Naming Oxyacids If polyatomic ion name ends in –ate, then change ending to –ic suffix. If polyatomic ion name ends in –ite, then change ending to –ous suffix. Write word acid at the end of all names. oxyanions ending with -ate oxyanions ending with -ite

56 © 2014 Pearson Education, Inc. 1. H 2 S 2. HClO 3 3. HC 2 H 3 O 2 Name the Following

57 © 2014 Pearson Education, Inc. hydrosulfuric acid chloric acid acetic acid 1. H 2 S 2. HClO 3 3. HC 2 H 3 O 2 Name the Following

58 © 2014 Pearson Education, Inc. Writing Formulas for Acids When name ends in acid, formulas starts with H. Write formulas as if ionic, even though it is molecular. Hydro- prefix means it is binary acid; no prefix means it is an oxyacid. For oxyacid –if ending is –ic, polyatomic ion ends in –ate. –if ending is –ous, polyatomic ion ends in –ous.

59 © 2014 Pearson Education, Inc. Acid Rain Certain pollutants—such as NO, NO 2, SO 2, SO 3 —form acids when mixed with water, resulting in acidic rainwater. Acid rain can fall or flow into lakes and streams, making these bodies of water more acidic.

60 © 2014 Pearson Education, Inc. Inorganic Nomenclature Flow Chart

61 © 2014 Pearson Education, Inc. Formula Mass The mass of an individual molecule or formula unit also known as molecular mass or molecular weight Sum of the masses of the atoms in a single molecule or formula unit whole = sum of the parts! Mass of 1 molecule of H 2 O = 2(1.01 amu H) amu O = amu

62 © 2014 Pearson Education, Inc. Molar Mass of Compounds The molar mass of a compound—the mass in grams of 1 mol of its molecules or formula units—is numerically equivalent to its formula mass.

63 © 2014 Pearson Education, Inc. Molar Mass of Compounds The relative masses of molecules can be calculated from atomic masses: formula mass = 1 molecule of H 2 O = 2(1.01 amu H) amu O = amu 1 mole of H 2 O contains 2 moles of H and 1 mole of O: molar mass = 1 mole H 2 O = 2(1.01 g H) g O = g so the molar mass of H 2 O is g/mole Molar mass = formula mass (in g/mole)

64 © 2014 Pearson Education, Inc. Using Molar Mass to Count Molecules by Weighing Molar mass in combination with Avogadro’s number can be used to determine the number of atoms in a given mass of the element. –Use molar mass to convert to the amount in moles. Then use Avogadro’s number to convert to number of molecules.

65 © 2014 Pearson Education, Inc. Composition of Compounds A chemical formula, in combination with the molar masses of its constituent elements, indicates the relative quantities of each element in a compound, which is extremely useful information.

66 © 2014 Pearson Education, Inc. Composition of Compounds Percentage of each element in a compound by mass Can be determined from 1. the formula of the compound and 2. the experimental mass analysis of the compound. The percentages may not always total to 100% due to rounding.

67 © 2014 Pearson Education, Inc. Conversion Factors from Chemical Formula Chemical formulas contain within them inherent relationships between numbers of atoms and molecules. –Or moles of atoms and molecules These relationships can be used to determine the amounts of constituent elements and molecules. –Like percent composition

68 © 2014 Pearson Education, Inc. Determining a Chemical Formula from Experimental Data Empirical Formula Simplest, whole-number ratio of the atoms of elements in a compound Can be determined from elemental analysis –Masses of elements formed when a compound is decomposed, or that react together to form a compound Combustion analysis –Percent composition Note: An empirical formula represents a ratio of atoms or a ratio of moles of atoms, not a ratio of masses.

69 © 2014 Pearson Education, Inc. Finding an Empirical Formula 1.Convert the percentages to grams. a)Assume you start with 100 g of the compound. b)Skip if already grams. 2.Convert grams to moles. a)Use molar mass of each element. 3.Write a pseudoformula using moles as subscripts.

70 © 2014 Pearson Education, Inc. Finding an Empirical Formula 4.Divide all by smallest number of moles. a)If the result is within 0.1 of a whole number, round to the whole number. 5.Multiply all mole ratios by a number to make all whole numbers. a)If ratio.5, multiply all by 2. b)if ratio.33 or.67, multiply all by 3. c)If ratio 0.25 or 0.75, multiply all by 4, etc. d)Skip if already whole numbers.

71 © 2014 Pearson Education, Inc. Molecular Formulas for Compounds The molecular formula is a multiple of the empirical formula. To determine the molecular formula you need to know the empirical formula and the molar mass of the compound. Molecular formula = (empirical formula)n, where n is a positive integer.

72 © 2014 Pearson Education, Inc. Molecular Formulas for Compounds The molar mass is a whole-number multiple of the empirical formula molar mass, the sum of the masses of all the atoms in the empirical formula: n = molar mass empirical formula molar mass

73 © 2014 Pearson Education, Inc. Combustion Analysis A common technique for analyzing compounds is to burn a known mass of compound and weigh the amounts of product made. –This is generally used for organic compounds containing C, H, O. By knowing the mass of the product and composition of constituent element in the product, the original amount of constituent element can be determined. –All the original C forms CO 2, the original H forms H 2 O, and the original mass of O is found by subtraction. Once the masses of all the constituent elements in the original compound have been determined, the empirical formula can be found.

74 © 2014 Pearson Education, Inc. Combustion Analysis

75 © 2014 Pearson Education, Inc. Chemical Reactions Reactions involve chemical changes in matter resulting in new substances. Reactions involve rearrangement and exchange of atoms to produce new molecules. –Elements are not transmuted during a reaction. Reactants  Products

76 © 2014 Pearson Education, Inc. Chemical Equations Shorthand way of describing a reaction Provide information about the reaction –Formulas of reactants and products –States of reactants and products –Relative numbers of reactant and product molecules that are required –Can be used to determine weights of reactants used and products that can be made

77 © 2014 Pearson Education, Inc.

78 Combustion of Methane Methane gas burns to produce carbon dioxide gas and gaseous water. –Whenever something burns it combines with O 2 (g). CH 4 (g) + O 2 (g)  CO 2 (g) + H 2 O(g) If you look closely, you should immediately spot a problem.

79 © 2014 Pearson Education, Inc. Combustion of Methane Notice also that the left side has four hydrogen atoms while the right side has only two. To correct these problems, we must balance the equation by changing the coefficients, not the subscripts.

80 © 2014 Pearson Education, Inc. Combustion of Methane, Balanced To show the reaction obeys the Law of Conservation of Mass the equation must be balanced. –We adjust the numbers of molecules so there are equal numbers of atoms of each element on both sides of the arrow. 1 C + 4 H + 4 O

81 © 2014 Pearson Education, Inc. Organic Compounds Early chemists divided compounds into two types: organic and inorganic. Compounds from living things were called organic; compounds from the nonliving environment were called inorganic. Organic compounds are easily decomposed and could not be made in the lab. Inorganic compounds are very difficult to decompose, but are able to be synthesized.

82 © 2014 Pearson Education, Inc. Modern Organic Compounds Today organic compounds are commonly made in the lab and we find them all around us. Organic compounds are mainly made of C and H, sometimes with O, N, P, S, and trace amounts of other elements The main element that is the focus of organic chemistry is carbon.

83 © 2014 Pearson Education, Inc. Carbon Bonding Carbon atoms bond almost exclusively covalently. –Compounds with ionic bonding C are generally inorganic. When C bonds, it forms four covalent bonds: –4 single bonds, 2 double bonds, 1 triple + 1 single, etc. Carbon is unique in that it can form limitless chains of C atoms, both straight and branched, and rings of C atoms.

84 © 2014 Pearson Education, Inc. Carbon Bonding

85 © 2014 Pearson Education, Inc. Hydrocarbons Organic compounds can be categorizing into types: hydrocarbons and functionalized hydrocarbons.

86 © 2014 Pearson Education, Inc. Hydrocarbons are organic compounds that contain only carbon and hydrogen. Hydrocarbons compose common fuels such as –oil, –gasoline, –liquid propane gas, –and natural gas. Hydrocarbons

87 © 2014 Pearson Education, Inc. Hydrocarbons containing only single bonds are called alkanes, while those containing double or triple bonds are alkenes and alkynes, respectively. Hydrocarbons consist of a base name and a suffix. –alkane (-ane) –alkene (-ene) –alkyne (-yne) The base names for a number of hydrocarbons are listed here: –1 meth2 eth –3 prop 4 but –5 pent 6 hex –7 hept 8 oct –9 non 10 dec Naming of Hydrocarbons Base name determined by number of C atoms Suffix determined by presence of multiple bonds

88 © 2014 Pearson Education, Inc. Common Hydrocarbons

89 © 2014 Pearson Education, Inc. Functionalized Hydrocarbons The term functional group derives from the functionality or chemical character that a specific atom or group of atoms imparts to an organic compound. –Even a carbon–carbon double or triple bond can justifiably be called a “functional group.” A group of organic compounds with the same functional group forms a family.

90 © 2014 Pearson Education, Inc. Functionalized Hydrocarbons

91 © 2014 Pearson Education, Inc. Families in Organic Compounds

92 © 2014 Pearson Education, Inc.

93 Practice — How many moles are in 50.0 g of PbO 2 ? (Pb = 207.2, O = 16.00) because the given amount is less than g, the moles being < 1 makes sense 1 mol PbO 2 = g 50.0 g mol PbO 2 moles PbO 2 Check: Solution: Conceptual Plan: Relationships: Given: Find: g PbO 2 mol PbO 2 93 Tro: Chemistry: A Molecular Approach, 2/e

94 © 2014 Pearson Education, Inc. Example: Find the number of CO 2 molecules in 10.8 g of dry ice because the given amount is much less than 1 mol CO 2, the number makes sense 1 mol CO 2 = g, 1 mol = x g CO 2 molecules CO 2 Check: Solution: Conceptual Plan: Relationships: Given: Find: g CO 2 mol CO 2 molec CO 2 94 Tro: Chemistry: A Molecular Approach, 2/e

95 © 2014 Pearson Education, Inc. Example 3.15: Find the mass of hydrogen in 1.00 gal of water because 1 gallon weighs about 3800 g, and H is light, the number makes sense L = 1 gal, 1 L = 1000 mL, 1.00 g H 2 O = 1 mL, 1 mol H 2 O = g, 1 mol H = g, 2 mol H : 1 mol H 2 O 1.00 gal H 2 O, d H2O = 1.00 g/ml g H Check: Solution: Conceptual Plan: Relationships: Given: Find: gal H 2 OL H 2 OmL H 2 Og H 2 O mol H 2 OmoL Hg H 95 Tro: Chemistry: A Molecular Approach, 2/e

96 © 2014 Pearson Education, Inc. Example 3.13: Find the mass percent of Cl in C 2 Cl 4 F 2 because the percentage is less than 100 and Cl is much heavier than the other atoms, the number makes sense C 2 Cl 4 F 2 % Cl by mass Check: Solution: Conceptual Plan: Relationships: Given: Find: 96 Tro: Chemistry: A Molecular Approach, 2/e

97 © 2014 Pearson Education, Inc. Practice — Benzaldehyde is 79.2% carbon. What mass of benzaldehyde contains 19.8 g of C? because the mass of benzaldehyde is more than the mass of C, the number makes sense 100 g benzaldehyde : 79.2 g C 19.8 g C, 79.2% C g benzaldehyde Check: Solution: Conceptual Plan: Relationships: Given: Find: g Cg benzaldehyde 97 Tro: Chemistry: A Molecular Approach, 2/e

98 © 2014 Pearson Education, Inc. Example 3.17 Laboratory analysis of aspirin determined the following mass percent composition. Find the empirical formula. C = 60.00% H = 4.48% O = 35.53% 98 Tro: Chemistry: A Molecular Approach, 2/e

99 © 2014 Pearson Education, Inc. Example: Find the empirical formula of aspirin with the given mass percent composition Write down the given quantity and its units Given:C = 60.00% H = 4.48% O = 35.53% Therefore, in 100 g of aspirin there are g C, 4.48 g H, and g O 99 Tro: Chemistry: A Molecular Approach, 2/e

100 © 2014 Pearson Education, Inc. Example: Find the empirical formula of aspirin with the given mass percent composition Write down the quantity to find and/or its units Find: empirical formula, C x H y O z Information Given:60.00 g C, 4.48 g H, g O 100 Tro: Chemistry: A Molecular Approach, 2/e

101 © 2014 Pearson Education, Inc. Example: Find the empirical formula of aspirin with the given mass percent composition Write a conceptual plan Information Given:60.00 g C, 4.48 g H, g O Find: empirical formula, C x H y O z g C mol C g H mol H pseudo- formula pseudo- formula empirical formula empirical formula mole ratio whole number ratio g O mol O 101 Tro: Chemistry: A Molecular Approach, 2/e

102 © 2014 Pearson Education, Inc. Example: Find the empirical formula of aspirin with the given mass percent composition Collect needed relationships 1 mole C = g C 1 mole H = g H 1 mole O = g O Information Given:60.00 g C, 4.48 g H, g O Find: empirical formula, C x H y O z CP: g C,H,O  mol C,H,O  pseudo form.  mol ratio  emp. form. 102 Tro: Chemistry: A Molecular Approach, 2/e

103 © 2014 Pearson Education, Inc. Example: Find the empirical formula of aspirin with the given mass percent composition Apply the conceptual plan –calculate the moles of each element 103 Information Given:60.00 g C, 4.48 g H, g O Find: empirical Formula, C x H y O z CP: g C,H,O  mol C,H,O  pseudo form.  mol ratio  emp. form. Rel: 1 mol C = g; 1 mol H = g; 1 mol O = g Tro: Chemistry: A Molecular Approach, 2/e

104 © 2014 Pearson Education, Inc. Example: Find the empirical formula of aspirin with the given mass percent composition Apply the conceptual plan –write a pseudoformula C H 4.44 O Information Given:60.00 g C, 4.48 g H, g O Find: empirical formula, C x H y O z CP: g C,H,O  mol C,H,O  pseudo form.  mol ratio  emp. form. Rel: 1 mol C = g; 1 mol H = g; 1 mol O = g Tro: Chemistry: A Molecular Approach, 2/e

105 © 2014 Pearson Education, Inc. Example: Find the empirical formula of aspirin with the given mass percent composition Apply the concept plan –find the mole ratio by dividing by the smallest number of moles Information Given:60.00 g C, 4.48 g H, g O Find: empirical formula, C x H y O z CP: g C,H,O  mol C,H,O  pseudo form.  mol ratio  emp. form. Rel: 1 mol C = g; 1 mol H = g; 1 mol O = g 105 Tro: Chemistry: A Molecular Approach, 2/e

106 © 2014 Pearson Education, Inc. Example: Find the empirical formula of aspirin with the given mass percent composition Apply the conceptual plan –multiply subscripts by factor to give whole number {C 2.25 H 2 O 1 } x 4 C9H8O4C9H8O4 Information Given:60.00 g C, 4.48 g H, g O Find: empirical formula, C x H y O z CP: g C,H,O  mol C,H,O  pseudo form.  mol ratio  emp. form. Rel: 1 mol C = g; 1 mol H = g; 1 mol O = g 106 Tro: Chemistry: A Molecular Approach, 2/e


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