Unit 3 Topics: Covalent, ionic, & acids: naming and writing formulas*

1. AP Chemistry Unit 3 Topics: • Covalent, ionic, & acids: naming and writing formulas* • Balancing chemical equations • Decomposition, composition reactions, and combustion : predicting products • % composition • Empirical vs. Molecular formulas: “combustion train” calculation • Stoichiometry conversions, limiting reagents, % Yield * You will not have formal notes for writing the formulas for compounds. Instead, we will just do practice problems until you get the hang of it. If you need “formal notes”, you can go to my website and download the 1st year Accelerated Chemistry Notes for “Naming and Writing Formulas”.

2. Naming Compounds • Covalent Molecules– Contains only 2 nonmetals. • They are formed by sharing e−between atoms. • General Format: • Prefix (except mono)-name 1st elementprefix-name 2nd element ending in –ide

3. Naming Compounds • Ionic Compounds – Starts with metallic cation (or NH4+). • Formed when atoms transfer e− from a metal to a nonmetal. • General Format • Cation NameAnion Name • On a later quiz, you will have to memorize the cation and anion symbols & charges on the Ion Sheet. For this unit, I will let you use the Ion Sheet.

4. Naming Compounds • Acids– Starts with “H”

5. Balancing Equations • You can only change coefficients. • You can only use whole #’s. • Example: C3H8 + __O2__CO2 + __H2O 3 4 5 Decomposition Reactions • A reaction that breaks apart ______ ______________ into simpler substances, (usually two elements or an element and a smaller compound.) • General Form: _____  ___ + ___ • Examples: H2O  _____ + _____ • KClO3 _____ + _____ • Remember that “HONClBrIF” elements are diatomic when alone!! • Don’t try to balance it until you have correctly written the products!! one compound + AX A X H2 O2 O2 KCl

6. Categories of Decomposition (and Composition ) Reactions CaO CO2 NaCl O2 a) carbonates  metallic oxide + CO2CaCO3 _____ + _____ b) chlorates  metallic chloride + O2NaClO3 _____ + _____ c) hydroxides  metallic oxide + H2O Mg(OH)2 _____ + _____ d) oxy acids  nonmetal oxide + H2O H2SO4 _____ + _____ e) binary compounds  2 elements NaCl  _____ + _____ • Notice that in carbonates, hydroxides, and oxy acids, the oxygen combines with both the metal AND the nonmetal!! • Every time you try to write the formula for a new ionic compound, you must look up the ___________ of the ions and ___________ them if they are different!! MgO H2O SO3 H2O Na Cl2 charges cross

7. Composition Reactions two substances one compound This reaction category is sometimes called “Combination” or “Synthesis” • A reaction of _____ __________________, typically a metal and a nonmetal to form ______ ______________. • It is the opposite of decomposition. The same categories of reactions apply. It’s just in reverse! General Form: ___ + ___  _____ Examples: Al + Cl2 _______ PbO + H2O  ______ + A X AX AlCl3 2 elements binary compound Pb(OH)2 metallic + water oxide  hydroxide

8. Combustion Reactions CO2 H2O • A reaction between O2 and a compound containing Carbon, Hydrogen, (and sometimes Oxygen). • The products are always the same… ________ + ________ • This reaction is too easy!! Don’t miss it! General Form: CxHy + O2 ____ + ____ Examples: C2H2 + O2 _______ + _______ C7H6O + O2 _______ + _______ CO2 H2O CO2 H2O CO2 H2O

9. Percent Composition (by mass) AW stands for the atomic weight of the atom from the periodic table. FW stands for the formula weight of the compound, i.e.--the “molar mass”. AW and FW are nicknamed the “W.O.T.C.” (the weight on the chart) or the “Wizzle on the Chizzle”. Here’s another formula for % compostion:

10. Empirical Formulas Helpful Rhyme: % to mass, mass to mole, divide by small, times ’til whole. • The molecular formula is a whole # multiple of the empirical formula. • When given the molecular weight of the compound, you can compare the “empirical mass” to the “molecular mass” to see what this whole # multiple will be. (We will practice this calculation later.)

11. “Combustion Train” Dehydrite [Mg(ClO4)2•3H2O] and ascarite (NaOH on asbestos) A weighed quantity of the substance to be analyzed is placed in a combustion train and heated in a stream of dry O2. All the H in the compound is converted to H2O(g) which is trapped selectively in a previously weighed absorption tube. All the C is converted to CO2 (g) and this is absorbed selectively in a second tube. The increase of mass of each tube tells, respectively, how much H2O and CO2 were produced by combustion of the sample.

12. EXAMPLE 1: A 6.49-mg sample of ascorbic acid (vitamin C) was burned in a combustion train and 9.74 mg CO2 and 2.64 mg H2O were formed. Determine the empirical formula of ascorbic acid. Steps to Follow: • Calculate the moles of Carbon and Hydrogen in the compound. • Calculate the moles of Oxygen (if any) in the compound. (Sometimes other elements are present, such as Nitrogen, but you will be given a way to find these masses as well.) • The mole ratios are the subscripts of the empirical formula. Use the “Empirical Formula Rhyme” to complete the rest of the problem. Ans: C3H4O3

13. EXAMPLE 2: The combustion of 62.63 grams of a compound which contains only C,H and O yields 134.43 grams of CO2 and 13.75 grams of H2O. What is the empirical formula of the compound? Ans: C2HO • If the compound’s molecular weight is 156 g/mol, determine the molecular formula. Ans: C8H4O4 EXAMPLE 3: The combustion of 40.10 g of a compound which contains only C, H, Cl and O yields 58.57 g of CO2 and 14.98 g of H2O. Another sample of the compound with a mass of 75.00 g is found to contain 22.06 g of Cl. What is the empirical formula of the compound? • (Hint: Use the mass data to calculate the % composition of each element in the compound.) Ans: C4H5ClO2

14. Stoichiometry Conversion Factors • 1 mole = 22.4 L (at STP) = 6.02 x 1023 particles = Molar Mass in grams • These conversions will take up to 3 steps and no more! • Always convert to moles of the “given” first!

16. Limiting Reagent (or Reactant) • The reactant that runs out first “limits” the amount of product that can be formed. • Stoichiometry conversions can be done to determine which substance is the limiting reagent and how much of the excess is left over.

17. % Yield • The amount of product predicted from stoichiometry taking into account limiting reagents is called the theoretical yield. • This is the ideal amount of product that should be formed if all goes as planned in a “perfect world.” • The percent yield relates the actual yield (amount of material recovered in the laboratory) to the theoretical yield: