17
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 AP Chemistry * 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 1 st year Accelerated Chemistry Notes for “Naming and Writing Formulas”.

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

  • Upload
    nelson

  • View
    177

  • Download
    3

Embed Size (px)

DESCRIPTION

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 - PowerPoint PPT Presentation

Citation preview

Slide 1

Unit 3 Topics:Covalent, ionic, & acids: naming and writing formulas*Balancing chemical equations Decomposition, composition reactions, and combustion : predicting products % compositionEmpirical vs. Molecular formulas: combustion train calculation Stoichiometry conversions, limiting reagents, % Yield AP Chemistry* 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.

1

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

2 Ionic Compounds Starts with metallic cation (or NH4+).Formed when atoms transfer e from a metal to a nonmetal.General FormatCation Name Anion 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.

Naming Compounds

3Naming Compounds Acids Starts with H

4Balancing Equations You can only change coefficients. You can only use whole #s.Example: C3H8 + __O2 __CO2 + __H2O 345Decomposition 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!!Dont try to balance it until you have correctly written the products!! one compoundAXA XH2O2KClO2+

5Categories of Decomposition (and Composition ) Reactionsa) carbonates metallic oxide + CO2 CaCO3 _____ + _____b) chlorates metallic chloride + O2 NaClO3 _____ + _____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!! CaOCO2NaClO2MgOH2OSO3NaCl2chargescrossH2O

6This 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. Its just in reverse!

General Form: ___ + ___ _____

Examples: Al + Cl2 _______ PbO + H2O ______

Composition Reactionstwo substancesone compound AXAXAlCl3Pb(OH)2+ metallic + water oxide hydroxide 2 elements binary compound

7Combustion ReactionsA reaction between O2 and a compound containing Carbon, Hydrogen, (and sometimes Oxygen). The products are always the same ________ + ________ This reaction is too easy!! Dont miss it! General Form: CxHy + O2 ____ + ____Examples: C2H2 + O2 _______ + _______C7H6O + O2 _______ + _______

CO2H2OCO2H2OCO2H2OCO2H2O

8Percent 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.Heres another formula for % compostion:

9Empirical 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.)

10Combustion Train

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. Dehydrite [Mg(ClO4)23H2O] and ascarite (NaOH on asbestos)

11EXAMPLE 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

12EXAMPLE 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 compounds 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

13Stoichiometry Conversion Factors1 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!

14

15Limiting 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.

16% YieldThe 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:

17