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Mass Relationships in Chemical Reactions

Mass Relationships in Chemical Reactions. Chapter 3. 100. Natural lithium is: 7.42% 6 Li (6.015 amu) 92.58% 7 Li (7.016 amu). Average atomic mass of lithium:. = _______ amu. 3.1. Dozen = 12. Pair = 2. The mole (mol) is the amount of a substance that

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Mass Relationships in Chemical Reactions

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  1. Mass Relationships in Chemical Reactions Chapter 3

  2. 100 Natural lithium is: 7.42% 6Li (6.015 amu) 92.58% 7Li (7.016 amu) Average atomic mass of lithium: = _______ amu 3.1

  3. Dozen = 12 Pair = 2 The mole (mol) is the amount of a substance that contains as many elementary entities as there are atoms in exactly ______ grams of 12C 1 mol = NA =____________________ ___________________ number (NA) 3.2

  4. eggs shoes Molar mass is the mass of 1 mole of in grams marbles atoms 1 mole 12C atoms = ____________ atoms = ______ g 1 12C atom = 12.00 amu 1 mole 12C atoms = ___________ g 12C 1 mole lithium atoms = ___________ g of Li For any element ___________ (amu) = __________ (grams) 3.2

  5. One Mole of: S C Hg Cu Fe 3.2

  6. _____ g = ________________ amu 1 amu = ______________ g = molar mass in g/mol M NA= Avogadro’s number 3.2

  7. Do You Understand Molar Mass? How many atoms are in 0.551 g of potassium (K) ? 3.2

  8. 1S amu 2O amu SO2 SO2 amu Molecular mass (or molecular weight) is the sum of the atomic masses (in amu) in a molecule. For any molecule ________ mass (amu) = ______ (grams) 1 molecule SO2 = _________ amu 1 mole SO2 = ________ g SO2 3.3

  9. Do You Understand Molecular Mass? How many H atoms are in 72.5 g of C3H8O ? 3.3

  10. n x molar mass of element x 100% molar mass of compound C2H6O Percent composition of an element in a compound = n is the number of moles of the element in 1 mole of the compound 3.5

  11. Types of Formulas • ____________ Formula The formula of a compound that expresses the _________________ ratio of the atoms present. Ionic formula are always ____________ formula • _______ Formula The formula that states the _____ number of each kind of atom found in _________ of the compound.

  12. To obtain an Empirical Formula 1. Determine the _______________ of each element present, if necessary. • Calculate the number of _________ of each element. • Divide each by the smallest number of moles to obtain the_______________. • If _____numbers are not obtained* in step 3), multiply through by the _____ number that will give all whole numbers *Be careful! Do not round off numbers prematurely

  13. A sample of a brown gas, a major air pollutant, is found to contain 2.34 g N and 5.34g O. Determine a formula for this substance. require mole ratios so convert grams to moles

  14. Calculation of the Molecular Formula A compound has an empirical formula of NO2. The colourless liquid, used in rocket engines has a molar mass of 92.0 g/mole. What is the molecular formula of this substance?

  15. Empirical Formula from % Composition A substance has the following composition by mass: 60.80 % Na ; 28.60 % B ; 10.60 % H What is the empirical formula of the substance? Consider a sample size of _____ grams This will contain: _____ grams of Na, ______ grams of B, and _____ grams H Determine the number of ______ of each Determine the ________ number ratio

  16. g CO2 g H2O mol CO2 mol H2O mol C mol H g H g C Combust 11.5 g ethanol Collect 22.0 g CO2 and 13.5 g H2O 6.0 g C = 0.5 mol C 1.5 g H = 1.5 mol H g of O = g of sample – (g of C + g of H) 4.0 g O = 0.25 mol O Empirical formula C0.5H1.5O0.25 Divide by smallest subscript (0.25) Empirical formula C2H6O 3.6

  17. Mass Changes in Chemical Reactions • Write balanced chemical equation • Convert quantities of known substances into moles • Use coefficients in balanced equation to calculate the number of moles of the sought quantity • Convert moles of sought quantity into desired units 3.8

  18. Other units • Molarity • Moles solute / L solution • Gases • 22.4 L = 1 mole of ANY GAS at STP

  19. 2CH3OH + 3O2 2CO2 + 4H2O Methanol burns in air according to the equation If 209 g of methanol are used up in the combustion, what mass of water is produced? 3.8

  20. 6 green used up 6 red left over Limiting Reagents 3.9

  21. Method 1 • Pick A Product • ????? • The ____ answer will be the correct answer • The _____that gives the _____answer will be the _______ reactant

  22. Limiting Reactant: Method 1 • 10.0g of aluminum reacts with 35.0 grams of chlorine gas to produce aluminum chloride. Which reactant is limiting, which is in excess, and how much product is produced? 2 Al + 3 Cl2 2 AlCl3 • Start with Al: • Now Cl2:

  23. Method 2 • Convert one of the reactants to the _____ • See if there is enough _______ to use up the other ______ • If there is less than the ______amount, it is the ______ reactant • Then, you can find the desired species

  24. Do You Understand Limiting Reagents? 2Al + Fe2O3 Al2O3 + 2Fe In one process, 124 g of Al are reacted with 601 g of Fe2O3 Calculate the mass of Al2O3 formed. 3.9

  25. g Al mol Al mol Al2O3 g Al2O3 Use limiting reagent (Al) to calculate amount of product that can be formed. 3.9

  26. Finding Excess Practice • 10.0g of aluminum reacts with 35.0 grams of chlorine gas 2 Al + 3 Cl2 2 AlCl3 • We found that _______ is the limiting reactant, and _______ of aluminum chloride are produced. Given amount of excess reactant Amount of excess reactant actually used Note that we started with the limiting reactant! Once you determine the LR, you should only start with it!

  27. % Yield = x 100 _________Yield _________Yield ___________ is the amount of product that would result if all the limiting reagent reacted. _________ is the amount of product actually obtained from a reaction. 3.10

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