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Principles of Chemistry: A Molecular Approach, 1st Ed. Nivaldo Tro Chapter 3 Molecules, Compounds, and Chemical Equations Chapt 3 A. Ghumman Chapt 3 A. Ghumman Compounds The properties of the compound are totally different from the constituent elements. Compounds are composed of atoms held together by chemical bonds. Chapt 3 A. Ghumman 1 Chemical Bond and bond types Bonds are forces of attraction between atoms. The bonding attraction comes from attractions between protons and electrons Two general types of bonding: ionic and covalent Chapt 3 A. Ghumman Ionic bond Ionic bonds result when electrons have been transferred between atoms, resulting in oppositely charged ions that attract each other e.g.Na+Cl between metal atoms and nonmetal atoms (ionic compounds NaCl) Anion: An atom(a nonmetal) that picks up an extra electron becomes a negatively charged ion e.g. ClCation: An atom(metal) that loses electrons becomes a positively charged ion e.g. Na+. An ionic compound is a compound composed of cations and anions attracted to one another by electrostatic forces(ionic bonds)e.g. NaCl. Chapt 3 A. Ghumman Chapt 3 A. Ghumman Ionic bond 2 Covalent bond •Covalent bonds result when two atoms share some of their electrons. 9generally found when nonmetal atoms bond together (Molecular compounds) Chapt 3 A. Ghumman Representing Compounds with Chemical Formula Compounds are generally represented with a chemical formula. All formulas and models convey a limited amount of information—none are perfect representations. All chemical formulas indicates the elements present in the compound. Chapt 3 A. Ghumman Types of chemical Formulas Ionic compound s 1. Empirical Formula- Gives the relative number of atoms of each element in a compound Does not describe how many atoms, the order of attachment, or the shape. The formulas for ionic compounds are empirical The empirical formula for the ionic compound fluorspar is CaCl2.(one Ca2+for every 2 Cl- ions) The empirical formula for the molecular compound oxalic acid is CHO2.(actual formula is C2H2O4) Chapt 3 A. Ghumman 3 Types of Formulas 2. Molecular Formula-Gives the actual number of atoms of each element in a molecule of a compound Molecular formula is always whole-number multiple of empirical formula For some compound molecular formula is empirical formula e.g H2O does not describe the order of attachment, or the shape The molecular formula is C2H2O4, (E.F =CH2O) Chapt 3 A. Ghumman Types of chemical Formulas Structural Formula-shows how the atoms in a molecule are connected or bonded to each other. Uses lines to represent the covalent bonds Single covalent bond a single line = 2 shared electrons, Double covalent bond double line = 4 shared electrons, Triple covalent bond triple line ≡ 6 shared electrons, Chapt 3 A. Ghumman Representing Compounds— Molecular Models Amore accurate and complete way to specify a compound is with molecular models Ball-and-Stick Models Oxalic acid Space-Filling Models use interconnected spheres to show the electron clouds of atoms connecting together Chapt 3 A. Ghumman 4 Chapt 3 A. Ghumman An Atomic –level view of elements and compounds Atomic elements-exist in nature with single atom as their basic unit Molecular elements- exist as molecules (diatomic or polyatomic Molecular compounds-usually composed of two or more covalently bonded non-metals e.g. water is composed of H2O molecules, propane gas is composed of C3H8 molecules Chapt 3 A. Ghumman Molecular View of Elements and Compounds Chapt 3 A. Ghumman 5 Molecular Elements Certain elements occur as two-atom molecules. Rule of 7’s Other elements occur as polyatomic molecules. 7A P4, S8, Se8 H2 N2 7 O2 F2 Cl2 Br2 Chapt 3 A. Ghumman I2 Molecular and Ionic compounds Ionic compounds- compounds whose particles are cations(metal) and anions (nonmetal) bound together by ionic bonds Basic unit of ionic compound is the formula unit, the smallest, electrically neutral collection of of ions Polyatomic ions are composed of a group of covalently bonded atoms with an overall charge e.g. ClO- (hypochlorite ion) Chapt 3 A. Ghumman Sample Problem Classify each of the following as either an atomic element, molecular element, molecular compound, or ionic compound. aluminum, Al aluminum chloride, AlCl3 chlorine, Cl2 acetone, C3H6O carbon monoxide, CO cobalt, Co Chapt 3 A. Ghumman 6 Writing formula for Ionic compound 1. 2. 3. 4. 5. ¾ ¾ Write the symbol for the metal cation and its charge. Write the symbol for the nonmetal anion and its charge. Charge (without sign) becomes subscript for other ion. Reduce subscripts to smallest whole number ratio. Check that the sum of the charges of the cation cancels the sum of the anions. Compound must have no total charge; therefore, we must balance the numbers of cations and anions in a compound to get 0 charge. If Na+ is combined with S2−, you will need 2 Na+ ions for every S2− ion to balance the charges; therefore, the formula must be Na2S. Chapt 3 A. Ghumman Sample Problem Write the formula of a compound made from aluminum ions and oxide ions. Solution: Write the symbol for the metal cation Write the symbol for the nonmetal anion Charge (without sign) becomes subscript for other ion. Reduce subscripts to smallest whole number ratio Check that the total charge of the cations cancels the total charge of the anions. Chapt 3 A. Ghumman Practice—What are the formulas for compounds made from the following ions? potassium ion with a nitride ion + 3– K with N calcium ion with a bromide ion 2+ with Br– Ca aluminum ion with a sulfide ion 3+ with S2– Al Chapt 3 A. Ghumman 7 Naming Ionic compounds Write systematic name by simply naming the ions. if cation is: metal with only one type of ion = metal name metal with variable charge = metal name(charge in roman numeral) polyatomic ion = name of polyatomic ion if anion is: nonmetal = stem of nonmetal name + -ide polyatomic ion = name of polyatomic ion E.g. CuCl2 = copper (II)chloride CaO calcium oxide Chapt 3 A. Ghumman Chapt 3 A. Ghumman Metal cations Naming Monatomic Nonmetal Anion Determine the charge from position on the Periodic Table. Most of the main group metals form cations with the charge equal to their group number The charge on a monatomic anion for a nonmetal equals the group number minus 8 Most transition elements form more than one ion, each with a different charge To name anion, change ending on the element name to -ide. Chapt 3 A. Ghumman 8 Naming Binary Ionic Compounds for Metals with Invariant Charge 1. name metal cation first, name nonmetal anion second by changing the ending with –ide For example NaF -Sodium Fluoride LiCl Lithium Chloride MgO Magnesium Oxide Chapt 3 A. Ghumman Common cations of the Transitions metals Chapt 3 A. Ghumman Practice problem Name the following compounds. KCl MgBr2 Al2S3 Chapt 3 A. Ghumman 9 Naming Binary Ionic compounds containing metals that form cations with variable charges CrBr3 Chromium(III) bromide Chapt 3 A. Ghumman Determining the Charge on a Cation with Variable Charge Au2S3 1. 2. 3. 4. Determine the charge on the anion. Au2S3—The anion is S. Since it is in Group 6A, its charge is 2−. Determine the total negative charge. Since there are 3 S in the formula, the total negative charge is −6. Determine the total positive charge. Since the total negative charge is −6, the total positive charge is +6. Divide by the number of cations. Since there are 2 Au in the formula and the total positive charge is +6, each Au has a 3+ charge. Chapt 3 A. Ghumman Find the charge on the cation 1. TiCl4 2. CrO3 3. Fe3N2 Chapt 3 A. Ghumman 10 Naming binary Ionic compounds 1. TiCl4 titanium(IV) chloride 2. Fe2S3 iron(III) sulfide 3. PbBr2 lead(II) bromide Example—Writing Formula for Binary Ionic Compounds Containing Variable Charge Metal manganese(IV) sulfide Mn = (1) × (4+) = +4 S = (2) × (2–) = −4 Chapt 3 A. Ghumman Naming Polyatomic ions A polyatomic ion is an ion consisting of two or more atoms chemically bonded together and carrying a net electric charge. Name any ionic compound by naming cation first and then anion. − SO 4 NO 3 nitrate NO 2 nitrite See table 3.5 in the textbook Chapt 3 sulfate 2− − 2− SO 3 sulfite A. Ghumman Some Common Polyatomic Ions Name Formula Name Formula acetate C2H3O2– hypochlorite ClO– carbonate CO32– chlorite ClO2– chlorate ClO3– hydrogen carbonate (aka bicarbonate) HCO3– perchlorate ClO4– hydroxide OH– sulfate SO42– nitrate NO3– sulfite SO32– nitrite NO2– chromate CrO42– hydrogen sulfate (aka bisulfate) HSO4– dichromate Cr2O72– ammonium NH4+ hydrogen sulfite (aka bisulfite) HSO3– Chapt 3 A. Ghumman 11 Naming Ionic compounds containing polyatomic Ions Ionic compounds containing polyatomic ions are named in the same way except the name of polyatiomic ion is used when ever it occurs. For example NaNO2 sodium nitrite • Na2SO4 • Na2SO3 • AgCN • Ca(OCl)2 • Cd(OH)2 • KClO4 sodium sulfate Chapt 3 A. Ghumman Oxyanions Oxyanions- polyatomic ions containing oxygen and another element. They are named systematically according to the number of oxygen atoms in the ion If there are only two ions in the series, the one with more oxygen atoms is given the ending –ate. With fewer oxygen atoms is given the ending – ite. e.g. NO2NO3- Nitrite ion Nitrate ion Chapt 3 A. Ghumman OXyanions More than two ions in the series are named using following prefixes hypo means less than and per means more than ClOHypochlorit ClO2Chlorite ClO3Chlorate ClO4Perchlorate Chapt 3 A. Ghumman 12 Writing Formula for Ionic Compounds Containing Polyatomic Ion Write the formula for Iron(III) phosphate 1. Write the symbol for the cation and its charge. 2. Write the symbol for the anion and its charge. 3. Charge (without sign) becomes subscript for other ion. 4. Reduce subscripts to smallest whole number ratio. 5. Check that the total charge of the cations cancels the total charge of the anions. Chapt 3 A. Ghumman PracticeProblem What are the formulas for compounds made from the following ions? • aluminum ion with a sulfate ion • chromium(II) with hydrogen carbonate Chapt 3 A. Ghumman Hydrates A hydrate is a compound that contains water molecules weakly bound in its crystals. Hydrates are named from the anhydrous (dry) compound, followed by the word “hydrate” with a prefix to indicate the number of water molecules per formula unit of the compound. in formula, attached waters follow · CoCl2·6H2O CoCl2·6H2O = cobalt(II) chloride hexahydrate CaSO4·½H2O = calcium sulfate hemihydrate Chapt 3 Prefix No. of Waters hemi ½ mono 1 di 2 tri 3 tetra 4 penta 5 hexa 6 hepta 7 octa 8 A. Ghumman 13 Hydrates Hydrate Anhydrous CoCl2·6H2O CoCl2 Chapt 3 A. Ghumman Molecular compounds: Formulas and Names 1. 2. 3. Binary compounds composed of two nonmetals are usually molecular and are named using a prefix system. Common names- water (H2O) and ammonia(NH3) Write the full name of the first element in the formula. Write the name of the second element in the formula with an ide suffix. Use a prefix in front of each name to indicate the number of atoms. a) Never use the prefix mono- on the first element. Chapt 3 A. Ghumman Subscript—Prefixes 1 = mono not used on first nonmetal 2 = di3 = tri4 = tetra5 = penta6 = hexa7 = hepta8 = octa 9 = nona10 = deca- •Drop last “a” if name begins with a vowel. Chapt 3 A. Ghumman 14 Example—Naming Binary Molecular Here are some examples of prefix names for binary molecular compounds: SF sulfur tetrafluoride 4 ClO chlorine dioxide 2 SF sulfur hexafluoride 6 Cl O dichlorine heptoxide 2 7 BF3 -- NO2 -- PCl5 -- I2F7 --Chapt 3 A. Ghumman 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. not named as acid if not dissolved in water sour taste dissolve many metals like Zn, Fe, Mg; but not Au, Ag, Pt formula generally starts with H e.g., HCl, H2SO4 Chapt 3 A. Ghumman Acids Binary acids consist of a H+ ion and any single anion. For example, HCl is hydrochloric acid. An oxoacid is an acid containing hydrogen, oxygen, and another element. An example is HNO3, nitric acid. Chapt 3 A. Ghumman 15 Naming Binary Acids Write a hydro prefix. Base name of nonmetal name. Change ending on nonmetal name to -ic. Write the word acid at the end of the name. Acids: HCl(aq) hydrochloric acid Examples Naming compounds from its formula Writing the formula from name of the compounds Chapt 3 A. Ghumman Naming Oxyacids 1. 2. 3. Naming Oxyacids H2SO4(aq) Identify the anion. SO42− = sulfate If the anion has -ate suffix, change it to -ic. If the anion has -ite suffix, change it to -ous. SO42− = sulfate ⇒ sulfuric Write the name of the anion followed by the word acid. sulfuric acid Chapt 3 A. Ghumman Oxoacids and their anions Chapt 3 A. Ghumman 16 3.7-Formula mass and mole concept for compounds Atomic mass of an element is the average mass of Formula mass-the average mass of a molecule (or an atom of the element formula unit) of a compound also known as molecular mass or molecular weight sum of the masses of the atoms in a single molecule or formula unit mass of 1 molecule of H2O = 2(1.01 amu H) + 16.00 amu O = 18.02 amu Chapt 3 A. Ghumman Calculating Formula mass Calculate formula mass of calcium nitrate, Ca(NO3)2. Chapt 3 A. Ghumman Molar Mass of a compound Molar Mass- is the mass in grams of one mole of Molar Mass of a compound- the mass in grams of atoms of an element = its atomic mass one mole of its molecules or formula units Numerically equal to its formula mass in grams Examples e.g. H2O Formula Mass = 1 molecule of H2O = 2(1.01 amu H) + 16.00 amu O = 18.02 amu since 1 mole of H2O contains 2 moles of H and 1 mole of O Molar Mass = 1 mole H2O = 2(1.01 g H) + 16.00 g O = 18.02 g so the Molar Mass of H2O is 18.02 g/mole Chapt 3 A. Ghumman 17 Molar mass Calculation Calculate the molar mass of sucrose, C12H22O11. Chapt 3 A. Ghumman Mole and mass conversion: converting grams to molecules nA = mA(g)/MmA (g mol-1) a) Find the number of CO2 molecules in 10.8 g of dry ice. b) What is the mass of a drop of water containing 3.55 × 1022 H2O molecules? Chapt 3 A. Ghumman How many moles are in 50.0 g of PbO2? (Pb = 207.2, O = 16.00) Given: 50.0 g PbO2 Find: moles PbO2 Conceptual Plan: g PbO2 mol PbO2 Relationships: 1 mol PbO2 = 239.2 g Solution: Check: Since the given amount is less than 239.2 g, the moles being <1 makes sense. Chapt 3 A. Ghumman 18 Calculating Mass from moles Conversely, suppose we have 3.25 moles of glucose, C6H12O6 (molecular wt. = 180.0 g/mol). What is its mass? Chapt 3 A. Ghumman Practice Problem What is the mass of 4.78 × 1024 NO2 molecules? molecules mol NO2 Chapt 3 g NO2 A. Ghumman 3.8-Percent Composition of compounds The percent composition of a compound is the mass percentage of each element in the compound. We define the mass percentage of “A” as the parts of “A” per hundred parts of the total, by mass. That is, Mass % of A= mass of A in 1 mole of compound x 100% mass of 1 mol of the compound Chapt 3 A. Ghumman 19 Mass Percentages from Formulas Let’s calculate the percent composition of butane, C4H10. First, we need the molecular mass of C4H10. 4 carbons @ 12.0 amu/atom = 48.0 amu 10 hydrogens @ 1.00 amu/atom = 10.0 amu 1 molecule of C4 H10 = 58.0 amu Now, we can calculate the percentage amu C % C = 5848.0 .0 amu total × 100% = 82.8%C amu H % H = 5810.0 .0 amu total × 100% = 17.2%H Chapt 3 A. Ghumman Example 3.13- Find the mass percent of Cl in C2Cl4F2 a FCF refrigerant Given: Find: C2Cl4F2 % Cl by mass Conceptual Plan: Relationships: Solution: Check: Since the percentage is less than 100 and Cl is much heavier than the other atoms, the number makes sense. Chapt 3 A. Ghumman Mass Percent as a conversion Factor The mass percent tells you the mass of a constituent element in 100 g of the compound. The fact that CCl2F2 is 58.64% Cl by mass means that 100 g of CCl2F2 contains 58.64 g Cl. This can be used as a conversion factor. 100 g CCl F : 58.64 g Cl 2 2 Chapt 3 A. Ghumman 20 Practice problem Benzaldehyde is 79.2% carbon. What mass of benzaldehyde contains 19.8 g of C? gC g benzaldehyde Chapt 3 A. Ghumman Conversion factor from chemical formula Chemical formula gives us relationship between the moles(amounts) of substances not between the masses (in grams) of them Mass of compound mass element Chapt 3 moles moles element A. Ghumman Sample problems a)What mass of hydrogen is contained in 1.00 gallon of water? (dH2O = 1.00g ml-1 and I gallon =3.785L) Given: 1.00 gal H2O, dH2O = 1.00 g/mL Plan: gal H2O g H2 O L H2 O mol H2O Find: m= ?g H mL H2O g H2 O moL H gH b)Determine the mass of oxygen in 7.2 –g sample of aluminum sulfate,Al2(SO4)3. Chapt 3 A. Ghumman 21 Empirical Formula 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 decompose or react a. combustion analysis b. percent composition Chapt 3 A. Ghumman Finding an Empirical Formula from % composition 1) Convert the percentages to grams. a) assume you start with 100 g of the compound 2) Convert grams to moles. a) use molar mass of each element as conversion factor 3) Write a tentative formula using moles as subscripts. 4) Divide all subscripts (number of moles) by smallest subscript. a) If result is within 0.1 of whole number, round to whole number. 5) Multiply all mole ratios by a number to make all whole numbers. If ratio is a) 0.5, multiply all by 2 b) 0.33 or 0.67, multiply all by 3 c) 0.25 or 0.75, multiply all by 4 b) skip if already whole numbers Chapt 3 A. Ghumman Example 3.15 Laboratory analysis of aspirin determined the following mass percent composition. Find the empirical formula C = 60.00%, H = 4.48%, O = 35.53% Solution: Given: C = 60.00%, H = 4.48% ,O = 35.53% Find: empirical formula, CxHyOz Assume 100 g of sample. In 100 g sample of aspirin there are 60.00 g C, 4.48 g H, and 35.53 g O Chapt 3 A. Ghumman 22 Write a conceptual Plan . gg whole mole number empirical ratio empirical pseudo- ratio pseudoformula formula mol mol formula formula Convert g of C, H and O to moles using molar mass as conversion factor Chapt 3 A. Ghumman Example Cont’d write a tentative formula C 4.996H4.44O2.220 find the mole ratio by dividing by the smallest number of moles multiply subscripts by factor to give whole number {C2.25H2O1} x 4 C9H8O4 Chapt 3 A. Ghumman Practice example Determine the empirical formula of stannous fluoride, which contains 75.7% Sn (118.70g/mol) and the rest fluorine (19.00g/mol). Sn ggSn molSn Sn mol ggFF molFF mol mole pseudo- ratio pseudoformula formula Chapt 3 empirical empirical formula formula A. Ghumman 23 Molecular Formula Molecular formula (M.F)-gives the actual number of each type of atoms in a molecule Molecular formula may be same as the empirical formula May be a multiple of the empirical formula M.F = (E.F) x n Multiple (n ) = M.F. mass/ E.F mass Can derive % composition from a chemical formula To determine the molecular formula, you need to know the empirical formula and the molar mass of the compound. Chapt 3 A. Ghumman Molecular Formula For example, suppose the empirical formula of a compound is CH2O and its molecular weight is 60.0 g/mol. The molar mass of the empirical formula (the empirical formula mass) is only 30.0 g/mol. n = 60.0/30.0=2 This would imply that the molecular formula is actually the empirical formula doubled, or C2H4O2 Chapt 3 A. Ghumman Practice—Benzopyrene has a molar mass of 252 g/mol and an empirical formula of C5H3. What is its molecular formula? 1. Determine E.F mass C5 = 5(12.01 g) = 60.05 g 3.03 g H3 = 3(1.01 g) = C5 H3 = 63.08 g 2. Molar mass is given so calculate multiple ‘n’ 3. Mulitply E.F with n to obtain M.F Molecular Formula = {C5H3} × 4 = C20H12 Chapt 3 A. Ghumman 24 Empirical formula from combustion analysis Chapt 3 A. Ghumman Example 3.19 Combustion of a 0.8233-g sample of a compound containing only carbon, hydrogen, and oxygen produced 2.445 g CO2 and 0.6003 g H2O. Determine the empirical formula of the compound. 1. Write down the given quantity and its units. Given: compound = 0.8233 g CO2 = 2.445 g H2O = 0.6003 g Find: empirical formula, CxHyOz Chapt 3 A. Ghumman Write a conceptual plan: g CO2, H2O mol C, H, O mol CO2, H2O mol C, H pseudo formula Chapt 3 g C, H mol ratio g O mol O empirical formula A. Ghumman 25 Calculate the grams of C and H in CO2 and H2O Calculate the grams of O = mass of sample-(mass of O+mass H) Calculate the # of moles of C,H and O using their molar masses as conversion factor Write a tentative formula Find the mole ratio by dividing by the smallest number of moles Multiply subscripts by factor to give whole number, if necessary Write the empirical formula Chapt 3 A. Ghumman Sample Problem Combustion of 0.844 g of caproic acid(containing only C, H and O) produced 0.784 g of H2O and 1.92 g of CO2. Calculate the empirical formula for caproic acid. If the molar mass of caproic acid is 116.2 g/mol, what is the molecular formula of caproic acid? Chapt 3 A. Ghumman Chemical Reactions Reactions involve rearrangement and exchange of atoms to produce new molecules. Chemical reactions are represented by chemical equations Reactants →Products For example combustion of methane gas CH4 Chapt 3 A. Ghumman 26 Chemical Equations shorthand way of describing a reaction provides information about the reaction formulas of reactants and products states of reactants and products relative numbers of reactant and product molecules that are required To show the reaction obeys the Law of Conservation of Mass, the equation must be balanced. Chapt 3 A. Ghumman Writing chemical equations Methane gas burns to produce carbon dioxide gas and gaseous water. Whenever something burns, it combines with O2(g). CH4(g) + O2(g) → CO2(g) + H2O(g) We adjust the numbers of molecules so there are equal numbers of atoms of each element on both sides of the arrow. CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g) Chapt 3 A. Ghumman Balanced Chemical Equations This equation is balanced, meaning that there are equal numbers of atoms of each element on the reactant and product sides. To obtain the number of atoms of an element, multiply the subscript by the coefficient. 1←C→1 4←H→4 4←O→2+2 CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g) Chapt 3 A. Ghumman 27 Symbols Used in Equations symbols used to indicate state after chemical (g) = gas; (l) = liquid; (s) = solid (aq) = aqueous = dissolved in water energy symbols used above the arrow for decomposition reactions Δ = heat and hν = light Chapt 3 A. Ghumman Example 3.21 Write a balanced equation for the combustion of butane, C4H10. Write a skeletal equation: Balance atoms in more complex substances first: Balance free elements by adjusting coefficient in front of free element: C4H10(l) + O2(g) → CO2(g) + H2O(g) 4⇐C⇒1×4 C4H10(l) + O2(g) → 4 CO2(g) + H2O(g) 10 ⇐ H ⇒ 2 × 5 C4H10(l) + O2(g) → 4 CO2(g) + 5 H2O(g) 13/2 × 2 ⇐ O ⇒ 13 C4H10(l) + 13/2 O2(g) → 4 CO2(g) + 5 H2O(g) If fractional coefficients, {C4H10(l) + 13/2 O2(g) → 4 CO2(g) + 5 H2O(g)} × 2 multiply thru by 2 C4H10(l) + 13 O2(g) → 8 CO2(g) + 10 H2O(g) denominator: Check: 8 ⇐ C ⇒ 8; 20 ⇐ H ⇒ 20; 26 ⇐ O ⇒ 26 Chapt 3 A. Ghumman Practice Example Acetic acid reacts with the metal aluminum to make aqueous aluminum acetate and gaseous hydrogen.Write a balanced equation for the reaction Acids are always aqueous. Metals are solid except for mercury. Chapt 3 A. Ghumman 28 Practice Balance the following equations. O2 + P4 + As2S3 + PCl3 → POCl3 N2O → P4O6 + N2 O2 → As2O3 + SO2 Ca3(PO4)2 + H3PO4 Chapt 3 → Ca(H2PO4)2 A. Ghumman Key Skills Writing empirical and Molecular formulas Classification of substances as atom, molecules, Ionic or molecular compounds Naming ionic compounds, compounds containing polyatomic ion, Molecular compounds, Acids. Calculating Formula mass, using formula mass to count molecules by weighing Calculating mass percent composition Using chemical formula as a conversion(Mole concept) Obtaining empirical formula from (a) experimental data (b) from combustion analysis Obtaining molecular formula from empirical formula and molar mass Writing and Balancing chemical equations Chapt 3 A. Ghumman 29