Chapter 9, 10 study guide PDF

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Chapter 9 and 10 Study Guide Mass Percent Composition  Knowing amount of each element in a given compound  Intensive property (doesn’t depend on amount)  Deals with masses Determining Empirical Formula  Deals with ratio of atoms present in a compound  Must deal with moles  Ionic compounds are always empirical  (1) percent to mass (2) mass to moles (3) divide by small (4) multiply til whole Molecular Formula  Determined using the whole number multiplier (ratio of molecular to empirical) molecular mass  Whole Number Multiplier = empirical formula mass Combustion Analysis  CxHyOz + O2  H2O + CO2  Given: starting amount of CxHyOz, ending amount of H2O and CO2  Compute Empirical Formula: o Moles of C in CxHyOz because all C comes from CO2 o Moles of H in CxHyOz because all H comes from H2O o Mass of C in CxHyOz and mass of H in CxHyOz from the moles o Use above and subtract from starting mass of CxHyOz to calculate the mass of O in CxHyOz and then convert to moles of O in CxHyOz o Divide by small o Multiply til whole Stoichiometry Problems 1. Balance Equation 2. Convert the necessary masses to moles 3. Use balanced equation and mole ratio to calculate moles of product/reactant 4. Convert to mass, molarity, atoms, etc (whatever problem asks for) Yields  Theoretical yield: calculated quantity of product  Actual yield less because impurities, products lost to purification, side reactions o Determined by experiment actual yield x 100 o % Yield = theoretical yield Limiting Reagent  The reactant that limits the production of products do to the given amounts  All calculations must start from the LR  Determining the Limiting Reagent 1. Start with a balanced equation

2. Calculate moles of product, assuming that each of the reactants is the LR 3. The reactant yielding the least amount of product is the LR 4. The LR determines the maximum amount of a product that can form Solutions  Solutes – can be s, l, or g. its what’s dissolved  Solvents – most often liquid (not always). Its what the solvent is dissolved in  Solution - a homogeneous combination of solute and solvent Molarity 

Molarity =

moles of solute liters of solution

Crash Course in Solubility  All Group 1A (alkali metal ions) are soluble  All NO3- and acetates (CH3COO-) are soluble Dilutions  Addition of solvent does not change the amount of solute present. It only changes molarity  M1V1=M2V2 Net Ionic Equations  Cancel out spectator ions  Show what precipitates Calorimetry  Two types: (1) hot object to cold object (2) chemical rxn with heat transfer 1. Hot object being cooled in a coffee cup calorimeter a. qsystem = -qsurroundings b. qwater = -qmetal added c. mwater cwater (Tf – Ti water) = mmetal cmetal(Tf – Ti metal) i. Solve for Tf or whatever not given ii. Specific heat (c) in J/gC. Mass in g. temperature in Celcius 2. Chemical Reaction (combine two aqueous solutions that cause a precipitate) a. Determine mass of each aqueous solution added using the g/L b. Determine moles of each reactant and find the limiting reagent c. Using the amount of the limiting reagent to determine the mass of precip d. To determine change in temperature i. Calculate the qrxn by multiplying the moles of the LR by the ΔHrxn ii. Set the qrxn just calculated equal to mcΔT and solve for ΔT...