Mole



MolesHow can we count how many atoms or molecules are in a piece of matter if we can’t see them?How can we count how many atoms or molecules are in a piece of matter if they have different masses?What can we measure in the laboratory that will help us?What is the “common currency”?MOLES!1 mole = the amount of pure substance that contains as many particles (atoms, molecules, or fundamental units) as there are atoms in exactly 12 grams of carbon-12 (agreed upon by chemists and physicists in 1960/61)= 6.02 x 1023 particles = Avogadro’s numberMole comes from molekül (German) = moleculeMolecule comes from molecula (New Latin), meaning very small specimen Background:Lorenzo Romano Amedeo Carlo Avogadro (1776-1856) - Italian physics professor1811 - Avogadro's hypothesis - now a law"Equal volumes of gases under the same conditions have equal numbers of molecules." “universal container”Late 1800s – chemists – developed scale of relative atomic masses of gases, based on 1/16 of the average atomic mass of oxygen1920s – physicists – developed relative atomic masses based on 1/16 of the oxygen-16 atom1959-1961 – chemists and physicists - agreed to switch to carbon-12 as the standard, setting its atomic mass at 12 (pragmatic reasons – carbon-12 was the standard in mass spectroscopy, and close to chemistry’s oxygen standards)Moles in conversion factorsnumber of “particles” ???moles6.02 x 1023 particles1 molemass (g) ?? moles average atomic mass in g1 molenumber of “particles” ?? mass (g)both of the above conversion factorsnumber of atoms in a compound# atoms1 compoundMath and the Mole(# particles/mole)How many fingers are there on 1 person?How many fingers are there on 1 dozen people?How many fingers are there on 3 dozen people?How many fingers are there on 1 mole of people?How many fingers are there on 3.12 moles of people?How many F atoms in 3.12 moles of F?How many moles of F do you have if you have 2.45 x 1022 atoms of F?(mass/mole)Hint: if problem includes numbers of atoms or other representative particles and moles, use Avogadro’s number: 6.02 x 1023 particlesIf problem includes grams and moles use the periodic table to find molar mass.How many grams of F are in 3.89 moles of F?How many moles of F atoms are in 45.6 g of F?(# particles/mass)How many F atoms are in 65.8 g F?What is the mass, in grams, of 7.62 x 1024 F atoms? (# atoms/compound)How many F atoms are in 3.84 moles of MoF6 molecules?Molar MassMolar mass = mass, in grams, of 1 mole of a substance (6.02 x 1023 particles)expressed in g/molMolar mass is numerically equal to average atomic mass in amus (atomic mass units).So, molar mass of oxygen (O) = mass of 1 mole of O atoms = mass of 6.02 x 1023 atoms = 16.00 g/molmolar mass of lead (Pb)= mass of 1 mole of Pb atoms= mass of 6.02 x 1023 atoms= 207.2 g/mol How do we determine the molar mass of compounds?Add up the molar masses of all elements in the compound, taking into account the number of moles of each element.e.g. What is the molar mass of Na3PO4?3 moles of Na @ 22.99 g/mol = 3 mol x 22.99 g mol1 mole of P @ 30.97 g/mol = 1 mol x 30.97 g mol4 moles of O @ 16.00 g/mol = 4 mol x 16.00 g molAdd these together = 163.94 g = molar mass of Na3PO4How do we use molar mass of a compound in a conversion problem?The same way we use molar mass of an atom…(#atoms/compound and molar mass of compounds)How many Na atoms are in 252 g of Na3PO4?Moles Warmups1.How many moles of Cu are in 4.95 g of Cu? A: 0.0779 mol Cu2.How many atoms of Cu are in 5.00 mol of Cu? A: 3.01 x 1024 Cu atoms3.How many grams of Na are in 5.29 moles Na? A: 122 g Na4.How many moles of Ba are in 5.25 x 1039 atoms of Ba? A: 8.72 x 1015 mol Ba5.What is the mass (in g) of 7.5 x 1015 atoms of Ni? (hint: 2 conversion factors)A: 7.3 x 10-7 g Ni6. How many atoms of Na are in 25 g of Na? (hint: 2 conversion factors)A: 6.5 x 1023 Na atoms7. What is the molar mass of calcium chloride (CaCl2)? A: 110.98 g/mol8.How many O atoms are in 2.9 moles of SO3? A: 5.2 x 1024 O atoms9. How many Ca atoms are in 532 g of Ca? A: 7.99 x 1024 Ca atoms10. How many grams of Pb are in 4.20 x 1022 atoms of Pb? A: 14.5 g Pb11. How many K atoms are in 16.2 g of K2S?A: 1.77 x 1023 K atoms12. What is the molar mass of barium nitrate (Ba(NO3)2? A: 261.35 g/mol13. What is the mass of 5.26 mol of NaOH? A: 210. g NaOH14. What is the mass of 5.62 x 1019 formula units of CuSO4? A: 1.49 x 10-2 g15. How many hydrogen atoms are in 562 g of ethanol (C2H6O)? A: 4.41 x 1025 H atomsMolar Calculations relating to Chemical FormulasWarmup: What is the molar mass of Pb3(PO4)2?Determine percent composition (by mass) of all elements present in a compound:Find the molar masses of each element in the compound.Find the total molar mass.Calculate:% composition = molar mass of element x 100% total molar mass of compounde.g. What is the % composition (by mass) of NaCl? CaCl2?Apply % composition: e.g. What mass of Na is present in 200.0 g NaCl?Mass Percent Warmups1. Copper (I) sulfide is found in nature as the mineral chalcocite, a copper ore. What is the mass percent of copper in chalcocite? A: 79.85% Cu 2. Chalcopyrite has the formula CuFeS2. What is the mass percent of copper in chalcopyrite? A: 34.6% Cu3. Will you get more copper from the same mass of pure chalcopyrite or pure chalcocite? Explain your answer.2. Convert % composition (mass percent) empirical formulaAssume a 100 g sample – use same numbers as grams rather than % .Perform mass mole conversions.Divide each result (mole) by the smallest result present (mole ratio).Look for whole number ratio.Rhyme to remember order of steps to convert % composition empirical formula:Percent to massMass to moleDivide by smallTimes till wholePractice:1. One of the components of fresh alkaline batteries is a black powdery compound, made of 63% manganese and 37% oxygen. What is the compound’s empirical formula?2. While analyzing a dead alkaline battery, Antonio found a compound that is made of 70.0% manganese and 30.0% oxygen. What is its empirical formula?Empirical Formula Warmups1.During a winter vacation, you work at a ski resort covering icy sidewalks with a substance containing 26.2% N, 7.5% H, and 66.3% Cl. What is the formula for this compound? A: NH4Cl2.Phosphorus forms two oxides. One has 56.34% P and 43.66% O. The other has 43.64% P and 56.36% O. What are the empirical formulas for these compounds?A: P2O3 and P2O53.What is the empirical formula for a compound that contains 26.56% potassium, 35.41% chromium, and 38.03% oxygen? A: K2CrO74.What is the empirical formula for a compound that contains 111.16 g of iron and 63.84 g of sulfur? A: FeS3. How to determine molecular formulaEmpirical vs. Molecular FormulaCompoundEmpirical formulaEmpiricalmolar massMolecularmolar massMolecular formulaFormaldehydeCH2O30.03 g30.03 gCH2OAcetic acidCH2O30.03 g60.06 gC2H4O2GlucoseCH2O30.03 g180.18 gC6H12O6To find the molecular formula of glucose,divide the molecular molar mass by the empirical molar mass, round to the nearest whole number.(molecular) molar mass = 180.18 g = ~ 6empirical molar mass 30.03 gthen multiply subscripts by 6 => C6H12O6 to get the molecular formulaPractice Problem – Determining molecular formulaHydrazine is 87.42% N and 12.58% H. The (molecular) molar mass of hydrazine is 32.0 g/mol.a) What is its empirical formula?b) What is its molecular formula?Solution Concentration Percent by MassMass % of component = mass of component in solution x 100% total mass of solutione.g. In order to maintain a sodium chloride (NaCl) concentration similar to ocean water, an aquarium must contain 3.6 g NaCl per 100.0 g of water. What is the percent by mass of NaCl in the solution? 3.6 g NaCl x 100% = 3.6 g NaCl x 100% 100.0 g H2O + 3.6 g NaCl 103.6 g total= 3.5%e.g. A solution contains 2.7 g of CuSO4 in 75 mL of solution. Assume the density of the solution is 1.0 g/mL. What is the mass percent of the solution?2.7 g (1 mL) x 100% = 3.6% 75 mL 1.0 gMolarity Molarity = the # moles solute dissolved in 1 L of solutionMolarity: the concentration of solution in moles solute315976014732000 L solution not solventSee Moles WS 6 for notes and practice problems related to molarity. ................
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