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coefficients give ratios

coefficients give ratios. To relate coefficients to ratios of reactants and products and reaction completion. coefficients of a balanced equation give the ratio of molecules in the reaction ___ H 2 (g) + ___ O 2 (g)  ___ H 2 O (l)

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coefficients give ratios

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  1. coefficients give ratios To relate coefficients to ratios of reactants and products and reaction completion. coefficients of a balanced equation give the ratio of molecules in the reaction ___ H2 (g) + ___ O2 (g)  ___ H2O (l) ___ molecules of hydrogen gas react with ___ molecules of oxygen gas to give ___ molecules of water

  2. Correct Ratio of molecules 2H2 : 1O2 : ?H2O 2 hydrogen molecules 1 oxygen molecule 2 water molecules

  3. Wrong Ratio of molecules 1H2 : 1O2: ?H2O 1 hydrogen molecule 1 oxygen molecule ?

  4. BUT… Can you “measure out” 2 molecules of hydrogen and 1 molecule of water in the lab??? Why or why not??? What unit do we use to measure in the lab? How many molecules are in one gram?

  5. Since one gram contains a huge amount of molecules or atoms... chemistshave devised a special counting unit to understand the large numbers of molecules or atoms measured in the lab. This unit is called the mole!

  6. What is a “counting unit”? • Bakers use the counting unit“dozen”to understand they have 12 donuts • Pencils are sold by the“gross”. If you buy 1 “gross” you will get 144 pencils. LiNkEd • give relationships between units

  7. Practice using a graphic organizer If you had 9454 pencils; calculate how many gross you would have. (remember 1 gross = 144 pencils)

  8. Practice – using relationships to give Conversion Fractions How many eggs are in 3.5 dozen? If you have 7.3 gross of pencils; how many individual pencils would you have ?

  9. What is a mole? To relate moles of a substance to the number of particles • a “mole” is the counting unit for particles in chemistry • A mole is the amount of matter (grams) that as many particles as there are numbers of atoms in exactly 12g of isotopically pure 12C But how much is that??? LiNkeD

  10. Mole Facts • Scientists have experimentally determined that 12g of 12C is made up of 6.02 x 1023atoms of 12C • Scientists call 6.02 x 1023 Avogadro’s Number LINKED

  11. So…Examples 1 mol of H2O = 6.02 x 1023 molecules H2O 1 mol of NO3- = 1 mol of Al = 1 mol of rice = 6.02 x 1023 ions of NO3- 6.02 x 1023 atoms Al 6.02 x 1023 grains of rice (this much rice would cover all the land area of the Earth to a depth of about 75 meters of rice)

  12. It would take over 19 million years to spend Avogadro's number of dollars if the money were spentat the rate of one billion dollars per second.

  13. Practice Calculate how many sodium atoms are in 0.120 mole of Na. How many moles of potassium is 1.25 x 1021 atoms of K?

  14. Molar Mass (MM) To state the mass of Avogadro’s number of atoms for any element referring to the periodic table. Since 1mol always has the 6.02x1023 particles, and (by definition) 1mol 12C has a mass of 12g… 1mol of 24Mg must have a mass of 1 atom of 12C = 12amu  1mol 12C = 12grams 1atom of 24Mg = 24amu  1mol 24Mg = 24grams 24g

  15. Molar Mass (MM) The mass of a single atom of an element (in amu) is numerically equal to the mass (in grams) of 1mol of that element The molar mass of an element is equal to its atomic mass (in grams) 1 mol Zn = _____ g 1mol Al = _____ g

  16. Practice How many atoms of Zn are in 2.3 mole of Zn? Determine the # of moles 4.39 x 1034 atoms Al makes up.

  17. Practice What is the mass (in grams) of 2.01 x 1022 atoms of S? How many atoms make up 2.34g Ca?

  18. Molar Mass To calculate the molar mass of a substance given its chemical formula. of a compound is calculated by adding the molar masses of each element What is the Molar Mass Fe2O3 ??? Molar Mass of… Fe :1 mol Fe = 55.85g Fe O : 1 mol O = 16g O So, for Fe2O3 : 2(55.85g Fe) + 3 (16.00 g O) = 159.7g/mol

  19. Practice How many grams does 1 mole of Mg(NO3)2 weigh? How many grams does 2.39 mole Mg(NO3)2 weigh?

  20. Practice How many N atoms are there in 4.31g of Mg(NO3)2 ? How many moles is 13.45 g of Mg(NO3)2 ?

  21. What happens when chemists make new compounds in the lab??? Synthetic chemist – makes new compounds Analytical chemist – “analyzes” new compound to give experimental evidence of its Composition and formula Percent Composition Empirical Formula Molecular Formula

  22. Percent Composition To calculate the percent composition of a compound given its chemical formula. Analytical chemist determines that a 100 g sample of a new compound contains 55g of element X and 45 g of element Y. What is the percent composition by mass of each element?

  23. Percent Composition Assume you have a total of one mole NaHCO3 Determine the percent by mass of each element in sodium hydrogen carbonate. ((The sum of the percents should be 100%)) KnownUnknown formula = NaHCO3 % Na = ? % H = ? % C = ? % O = ?

  24. Empirical Formula To calculate empirical formula of a compound given its percent composition • is the simplest whole-number ratio of elements present • may or may not be the same as the molecular formula Example : “hydrogen peroxide” empirical formula = HO molecular formula = H2O2

  25. Empirical Formula The % composition of an oxide of sulfur is 40.05% S and 59.95% O. Determine the empirical formula. • Assume total mass = 100g • Thus given percents = masses • 40.05g S and 59.95g O • Convert mass to moles of each • (this gives the mole ratio AND MUST be whole numbers in order to be used as subscripts!!) • Element with the smaller # of moles will have smallest possible subscript of 1

  26. Empirical Formula Methyl Acetate is a solvent commonly used in some paints, inks, and adhesives. Determine the empirical formula of methyl acetate, which has the following chemical analysis: 48.64% carbon 8.16% hydrogen 43.20% oxygen

  27. Molecular Formula To calculate molecular formula of a compound given its empirical formula. • specifies actual # of atoms of each element in one molecule (or formula unit) • To calculate: “n” being the integer used to multiply by to get molecular formula

  28. Molecular Formula The empirical formula for fructose (fruit sugar) is CH2O. The experimentally determined molar mass is 180g/mole, find the actual molecular formula for the sugar.

  29. Stiochiometry To relate the coefficients in a balanced equation to moles of reactant & product • relationship of quantities (mass or volume) in a chemical reaction according to the coefficients of a balanced equation • used to “determine” quantities of reaction (“how much” of one substance will react to make “how much” another substance) Linked

  30. Example: SMOG NO2 2 2 NO + O2 NO2 “2 molecules NO react with 1 molecule of O2 to give 2 molecules NO2” OR… “2000 molecules NO react with 1000 molecules O2 to give 2000 molecules NO2” OR… “ 2(6.02x1023)molecules NO react with 6.02x1023 molecules O2 to give 2(6.02x1023) molecules NO2” Linked LINKED

  31. Stiochiometry To relate the number of moles of two substances in a balanced equation. Remember that 6.02x1023 molecules = 1 mole of that substance so… 2 mole NO + 1 mole O2 2 mole NO2 Coefficients of a balanced equation indicate mole ratio of reactants and products

  32. Practice In the 19th Century, mercury (II) iodide was used as a treatment for syphilis; a reaction that produces Mercury (II) Iodide is: KI (aq) + Hg(NO3)2 (aq)  HgI2 (s) + KNO3 (aq) Dosages were very small, to make a 0.52g dose of mercury (II) iodide using this reaction how much potassium iodide would you need to start with?

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