Ch 10 Notes - Honors Chemistry

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Ch 10 Notes - Honors Chemistry

12/1/2011The MoleC H A P T E R 1 0T H E M O L E R E P R E S E N T S A L A R G E N U M B E RO F E X T R E M E L Y S M A L L P A R T I C L E SMeasuring Matter2S E C T I O N 1 0 . 1C H E M I S T S U S E T H E M O L E T O C O U N T A T O M S ,M O L E C U L E S , I O N S , A N D F O R M U L A U N I T S .Ch 10 - The MoleAmounts3The Mole4• How many gloves are there in a pair of gloves?• How many eggs are in a dozen eggs?• How many fireworks are in a gross of fireworks?• How many sheets are in a ream of paper?• How many atoms are in a mole of atoms?• A mole (mol) is the SI base unit used to measurethe amount of a substance◦ Defined as the number of carbon atoms in exactly 12 grams ofpure carbon-12◦ The amount of a mole is called Avogadro’s number (N A ) N A = 602,213,670,000,000,000,000,000 N A = 6.02 x 10 23 (you should learn this number) 1 mole of doughnuts is 6.02 x 10 23 doughnuts (yummy!) 1 mole of Au atoms is 6.02 x 10 23 atoms 1 mole of water molecules is 6.02 x 10 23 molecules 1 mole of Na + ions is 6.02 x 10 23 ionsCh 10 - The MoleCh 10 - The MoleConverting Moles to Particles• To convert the number of moles to the number ofparticles, use dimensional analysis and thisconversion factor5Practice Problem• Determine the number of atoms in 3.75 mol of Fe◦ 2.26 x 10 24 atoms Fe6• How many molecules are in 3.50 mol sucrose?• Calculate the number of formula units in 12.5 mol ofCaCO 3 .◦ 7.53 x 10 24 formula units CaCO 3Ch 10 - The MoleCh 10 - The Mole1


12/1/2011Converting Particles to Moles• To convert the number of particles to the number ofmoles, use dimensional analysis and this conversionfactor7Practice Problems• How many moles of CaCl 2 contain 1.26 x 10 24formula units of CaCl 2 ?◦ 2.09 mol CaCl 28• How many moles are 2.11 x 10 24 molecules ofsucrose?• How many moles of Ag contain 4.59 x 10 25 atoms ofAg?◦ 76.2 mol AgCh 10 - The MoleCh 10 - The MoleMoles and MassMass and the Mole9S E C T I O N 1 0 . 2A M O L E A L W A Y S C O N T A I N S T H E S A M EN U M B E R O F P A R T I C L E S ; H O W E V E R , M O L E SO F D I F F E R E N T S U B S T A N C E S H A V ED I F F E R E N T M A S S E S• How many atoms is 1 mole of Cu atoms?• How many atoms is 1 mole of Fe atoms?• What is the mass of 1 mol of Cu atoms?• What is the mass of 1 mol of Fe atoms?10Ch 10 - The MoleCh 10 - The MoleMolar Mass• The molar mass is the mass in grams of one moleof any pure substance◦ Units: g/mol◦ The molar mass of an element is numerically equal to itsatomic mass (periodic table) and has the units g/mol.11Converting Moles to Mass• To convert the number of moles to the mass (ingrams), use dimensional analysis and the molarmass as the conversion factor12molar mass• What is the mass of 3.00 mol Cu atoms?Ch 10 - The MoleCh 10 - The Mole2


12/1/2011Practice Problems13• Chromium is a component of chrome plating.Chrome plating is used on metals and in steel alloysto control corrosion. Calculate the mass in grams of0.0450 mol Cr.◦ 2.34 g Cr• Zirconium (Zr) is a metal used in nuclear reactorsbecause it is resistant to corrosion. What is the massof a sample that contains 4.05 mol of zirconium?◦ 369 g ZrConverting Mass to Moles• To convert the mass (in grams) to the number ofmoles, use dimensional analysis and the molar massas the conversion factorinverted molar mass• How many moles is 191 g Cu?14Ch 10 - The MoleCh 10 - The MolePractice Problems15• Calcium, the fifth most-abundant element on Earth,is always found combined with other elementsbecause of its high reactivity. How many moles ofcalcium are 525 g Ca?◦ 13.1 mol Ca• Titanium is Mr. Luzio’s favorite element and it isoften used to produce strong, lightweight alloys. Ifan alloy contains 645 g of titanium, how many molesof titanium are present?◦ 13.5 mol TiConverting between Atoms and Mass• A two step conversion is required to convert fromnumber of particles to mass and vice versa.• How many Au atoms are in 31.1 g Au?16Ch 10 - The MoleCh 10 - The MoleConverting between Atoms and Mass• A two step conversion is required to convert fromnumber of particles to mass and vice versa.• What is the mass of 5.50 x 10 22 atoms of He gas?17Practice Problems• Scandium (Sc) is a metal found in rare minerals thatare mined in Scandinavia. If a mineral samplecontains 25.6 g of scandium, how many atoms ofscandium are in the sample?◦ 3.42 x 10 23 atoms of Sc• Neon is the unreactive noble gas found in neonlamps. The gas gives off a reddish glow in theselamps. If a neon bulb contains 2.69 x 10 22 atoms ofneon, what is the mass of the neon?◦ 0.903 g Ne18Ch 10 - The MoleCh 10 - The Mole3


12/1/2011Summary• Use Avogadro’s Number to convert◦ # of particles # of moles• Use Molar Mass to convert◦ # of moles mass (in grams)• Use both Avogadro’s Number & Molar Mass toconvert◦ # of particles mass (in grams)19Homework• All “Practice Problems” in 10.1 & 10.2 (1-6, 15-21)◦ p323 1-4◦ p324 5-6◦ p328 15-16◦ p329 17-18◦ p331 19-21• SHOW ALL WORK AND INCLUDE UNITS!!20Ch 10 - The MoleCh 10 - The MoleMoles of CompoundsMoles of Compounds21S E C T I O N 1 0 . 3• How many atoms are there in 1 mol of C atoms?• What is the mass of 1 mol of C atoms?22T H E M O L A R M A S S O F A C O M P O U N D C A N B EC A L C U L A T E D F R O M I T S C H E M I C A L F O R M U L AA N D C A N B E U S E D T O C O N V E R T F R O M M A S ST O M O L E S O F T H A T C O M P O U N D .• How many atoms is 1 g of C atoms?• What’s the mass of 1 mol of CO 2 molecules?Ch 10 - The MoleCh 10 - The MoleFormulas and Moles• The formula of a compound represents the numberof atoms of each element in one molecule/formulaunit.◦ Therefore, the formula of a compound also represents thenumber of moles of atoms of each element in one mole of thecompound.23Calculating Molar Mass24• The molar mass (molecular weight) of acompound equals the molar mass of each elementmultiplied by the number of moles of that element inthe compound, added together• 1 mol of CO 2 contains◦ 1 mol of C atoms◦ 2 moles of O atomsCh 10 - The MoleCh 10 - The Mole4


12/1/2011Practice Problems• Hematite is the mineral form of iron(III) oxide.Determine the number of moles of oxide ions, O 2- ,contained in 6.25 mol Fe 2 O 3 .◦ 18.8 mol O 2-25Converting Moles to Mass• To convert the number of moles to the mass (ingrams), use dimensional analysis and the molarmass as the conversion factor26• What is the molar mass of iron(III) oxide?◦ 159.6 g/molmolar mass• What is the mass of 0.545 mol TiO 2 ?Ch 10 - The MoleCh 10 - The MolePractice ProblemsConverting Mass to Moles• The characteristic odor of garlic is due to annylsulfide, (C 3 H 5 ) 2 S. What is the mass of 2.50 mol of(C 3 H 5 ) 2 S?◦ 285.5 g• Baking soda, sodium bicarbonate, is a compoundused in many recipes. What is the mass of 1.25moles of baking soda?◦ 105 g NaHCO 327• To convert the mass (in grams) to the number ofmoles, use dimensional analysis and the molar massas the conversion factor• How many moles are 43.5 g of TiO 2 ?28inverted molar massCh 10 - The MoleCh 10 - The MolePractice Problems29• Calcium hydroxide is used to remove sulfur dioxidefrom the exhaust gases emitted by power plants andfor softening water by the elimination of Ca 2+ andMg 2+ ions. Calculate the number of moles of calciumhydroxide in 325 g of the compound?Converting between Molecules and Mass• A two step conversion is required to convert fromnumber of particles to mass and vice versa.30◦ 4.39 mol Ca(OH) 2• Calculate the number of moles in 5.67 g of potassiumhydroxide.◦ 0.101 mol KOH• What is the mass of 1 molecule of H 2 O?Ch 10 - The MoleCh 10 - The Mole5


12/1/2011Converting between Atoms and Mass• A two step conversion is required to convert fromnumber of particles to mass and vice versa.• How many molecules are 10 grams of water?31Practice Problems• Aluminum chloride is used in refining petroleum andmanufacturing rubber and lubricants. A sample ofaluminum chloride has a mass of 35.6 g.◦ How many aluminum ions are present? 1.61 x 10 23 Al 3+ ions◦ How many chloride ions are present? 4.83 x 10 23 Cl - ions32◦ What is the mass, in grams, of one formula unit of aluminumchloride? 2.21 x 10 -22 g/formula unit AlCl 3Ch 10 - The MoleCh 10 - The MoleSummary33Homework34• All “Practice Problems” in 10.3 (29-46)◦ p335 #29-36◦ p336 #37-39◦ p337 #40-41◦ p339 #42-46• SHOW ALL WORK AND INCLUDE UNITS!!Ch 10 - The MoleCh 10 - The MoleWolfram|Alpha35www.wolframalpha.comEmpirical and MolecularFormulas36S E C T I O N 1 0 . 4A M O L E C U L A R F O R M U L A O F A C O M P O U N D I SA W H O L E - N U M B E R M U L T I P L E O F I T SE M P I R I C A L F O R M U L A .Ch 10 - The MoleCh 10 - The Mole6


12/1/2011Percent Composition• The percent by mass of each element in a compoundis the percent composition of a compound37• A 100-g sample of a compound contains 55 g ofElement X and 45 g of Element Y, what is the percentcomposition of the compound?◦ The compound is 55% X and 45% YPercent Composition from the Formula• Because the formula is a ratio of moles of eachelement in 1 mole of the compound, the formula andmolar mass can be used to determine percent bymass• Calculate the percent composition of NaHCO 3 .◦ The molar mass of NaHCO 3 is 84.0 g/mol38Ch 10 - The MoleCh 10 - The MolePractice Problems• The chemical formula of caffeine is C 8 H 10 N 4 O 2 .Determine the percent composition of the molecule.◦ Molar mass = 194.2 g/mol39◦ 49.48 % C◦ 5.19 % H◦ 28.85 % N◦ 16.48 % O◦ K 2 Cr 2 O 7• Which compound has a greater percent by mass ofchromium, K 2 CrO 4 or K 2 Cr 2 O 7 ?Empirical Formula• The empirical formula for a compound is theformula with the smallest whole-number mole ratioof the elements.◦ The whole-number ratio gives the subscripts for the empiricalformula◦ May or may not be the molecular formula (HO for H 2 O 2 )• You can calculate the empirical formula from thepercent by mass by assuming that you have 100.0 gof the substance.• Convert the masses to moles and compare the moleratios40Ch 10 - The MoleCh 10 - The MoleExample• What is the empirical formula for a substance that is40.1% S and 59.9% O?◦ Assume 100.0 g of the substance 40.1 g S 59.9 g O◦ Calculate the number of moles of each element41Practice Problem• Methyl acetate is a solvent commonly used in somepaints, inks, and adhesives. Determine the empiricalformula for methyl acetate, which has the followingchemical analysis: 48.64% carbon, 8.16% hydrogen,43.20% oxygen.◦ C 3 H 6 O 242◦ Divide the number of moles of each element by the lowest number ofmoles◦ The mole ratio is 1:3, so the empirical formula is SO 3 .Ch 10 - The MoleCh 10 - The Mole7


12/1/2011Molecular Formula• To identify a specific compound, the molecularformula is necessary. The molecular formulaspecifies the actual number of atoms of each elementin one molecule or formula unit.◦ Different substances with the same empirical formula havedifferent molecular formulas and often have very differentproperties.• The molecular formula is always a whole numbermultiple of the empirical formula◦ Molecular formula = (empirical formula)n43Molecular Formula• Acetylene (a gas used for welding) and benzene (a liquidpossible carcinogen) have the same empirical formula(CH). If you experimentally determine the molar mass ofa compound, you can divide the actual molar mass by themass of the empirical formula to determine the value ofn.• Molecular formula = (empirical formula)n• The molecular formulas for acetylene and benzene areC 2 H 2 and C 6 H 6 respectively.44Ch 10 - The MoleCh 10 - The MoleEmpirical Formula & Molecular Formula45Practice Problem46• Succinic acid is a substance produced by lichens.Chemical analysis indicates it is composed of 40.7%carbon, 5.1% hydrogen, and 54.2% oxygen and has amolar mass of 118.1 g/mol. Determine the empiricaland molecular formulas for succinic acid.◦ Empirical formula = C 2 H 3 O 2◦ n = 2.00, so Molecular formula = C 4 H 6 O 4Ch 10 - The MoleCh 10 - The MolePractice Problem• The mineral ilmenite is usually mined and processedfor titanium, a strong, light, and flexible metal. Asample of ilmenite contains 5.41 g of iron, 4.64 g oftitanium, and 4.65 g of oxygen. Determine theempirical formula for ilmenite.◦ FeTiO 347Practice Problem• A molecule of nicotine contains 74.0% C, 8.65% H,and 17.35% N. The molar mass of nicotine is 162.3g/mol. Determine the empirical and molecularformula of nicotine.◦ Empirical formula = C 5 H 7 N◦ n = 2, so Molecular formula = C 10 H 14 N 248Ch 10 - The MoleCh 10 - The Mole8


12/1/2011Homework• All “Practice Problems” in 10.4 (54-66)◦ p344 54-57◦ p346 58-61◦ P350 62-66• SHOW ALL WORK AND INCLUDE UNITS!!49Formulas of Hydrates50S E C T I O N 1 0 . 5H Y D R A T E S A R E S O L I D I O N I C C O M P O U N D S I NW H I C H W A T E R M O L E C U L E S A R E T R A P P E DCh 10 - The MoleCh 10 - The MoleHydrates51Formulas of Hydrates52• A hydrate is an ionic compound with a specificnumber of molecules bound to its atoms◦ Forms as water molecules (called “waters of hydration”) aretrapped within the crystal lattice◦ Named using prefixes and the word “hydrate”◦ Formulas end with a dot, • , and the number of H 2 O• Example:◦ Na 2 CO 3 •10H 2 O sodium carbonate decahydrate• Used as desiccants – absorb moisture from the air tokeep other substances dryCh 10 - The MoleCh 10 - The MoleAnhydrous• When hydrates are heated, the water molecules arereleased and the anhydrous compound remains◦ The number of “waters of hydration” can be determined by massingthe hydrate and the anhydrous compound• What is the name/formula for a hydrate of bariumchloride if a 5.00 g sample of the hydrate leaves a 4.26 ganhydrous compound?53Practice Problem54• A mass of 2.50 g of blue, hydrated copper sulfate(CuSO 4 •xH 2 O) is placed in a crucible and heated.After heating, 1.59 g of white anhydrous coppersulfate (CuSO 4 ) remains. What is the formula for thehydrate? Name the hydrate.◦ CuSO 4 •5H 2 O◦ Copper(II) sulfate pentahydrate◦ BaCl 2 •2H 2 O◦ Barium chloride dihydrateCh 10 - The MoleCh 10 - The Mole9

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