Molar Conversions & Calculations Ch. 11 – The Mole

A. What is the Mole? VERY A large amount!!!! A counting number (like a dozen) Avogadro’s number (NA) 1 mol = 6.02  1023 items A large amount!!!! VERY

A. What is the Mole? HOW LARGE IS IT??? 1 mole of hockey pucks would equal the mass of the moon! 1 mole of basketballs would fill a bag the size of the earth! 1 mole of pennies would cover the Earth 1/4 mile deep!

B. Molar Mass Mass of 1 mole of an element or compound. Atomic mass tells the... atomic mass units per atom (amu) grams per mole (g/mol) Round to 2 decimal places

B. Molar Mass Examples carbon aluminum zinc 12.01 g/mol 26.98 g/mol

B. Molar Mass Examples water sodium chloride H2O 2 atoms H + 1 atom O 2(1.01) + 16.00 = 18.02 g/mol NaCl 1 atom Na + 1 atom Cl 22.99 + 35.45 = 58.44 g/mol

B. Molar Mass Examples sodium hydrogen carbonate sucrose NaHCO3 22.99 + 1.01 + 12.01 + 3(16.00) = 84.01 g/mol C12H22O11 12(12.01) + 22(1.01) + 11(16.00) = 342.34 g/mol

C. Percentage Composition the percentage by mass of each element in a compound

C. Percentage Composition Find the % composition of Cu2S. 127.10 g Cu 159.17 g Cu2S %Cu =  100 = 32.07 g S 159.17 g Cu2S %S =  100 =

C. Percentage Composition Find the percentage composition of a sample that is 28 g Fe and 8.0 g O. 28 g 36 g %Fe =  100 = 8.0 g 36 g %O =  100 =

C. Percentage Composition How many grams of copper are in a 38.0-gram sample of Cu2S? Cu2S is 79.852% Cu (38.0 g Cu2S)(0.79852) = g Cu

C. Percentage Composition Find the mass percentage of water in calcium chloride dihydrate, CaCl2•2H2O? 36.04 g 147.02 g %H2O =  100 =

Practice P. 322 #25; p. 331 #42, 43, 45 Answers on p. 929 and 930 P. 347 #111, 112; p. 348 #136

D. Molar Conversions molar mass 6.02  1023 MOLES (g/mol) IN GRAMS MOLES NUMBER OF PARTICLES (g/mol) (particles/mol) “Particles”= atoms, electrons, molecules, formula units, anything!

D. Molar Conversion Examples How many moles of carbon are in 26 g of carbon? 26 g C 1 mol C 12.01 g C = mol C

D. Molar Conversion Examples How many molecules are in 2.50 moles of C12H22O11? 6.02  1023 molecules 1 mol 2.50 mol

D. Molar Conversion Examples Find the mass of 2.1  1024 molecules of NaHCO3. 2.1  1024 molecules 1 mol 6.02  1023 molecules 84.01 g 1 mol

Practice P. Answers on p. 929 and 930

C2H6 CH3 E. Empirical Formula Smallest whole number ratio of atoms in a compound C2H6 reduce subscripts CH3

E. Empirical Formula 1. Find mass (or %) of each element. 2. Find moles of each element. -go out about 4 or 5 decimals 3. Divide moles by the smallest # to find subscripts. 4. When necessary, multiply subscripts by 2, 3, or 4 to get whole #’s.

E. Empirical Formula Poem to help you remember… Percent to mass Mass to mole Divide by small Multiply ‘til whole!

E. Empirical Formula Find the empirical formula for a sample of 25.9% N and 74.1% O. 25.9 g 1 mol 14.01 g = 1.8487 mol N 1.8487 mol 74.1 g 1 mol 16.00 g = 4.63125 mol O

N2O5 N1O2.5 E. Empirical Formula Need to make the subscripts whole numbers  multiply by 2 N2O5

CH3 C2H6 F. Molecular Formula “True Formula” - the actual number of atoms in a compound CH3 empirical formula ? C2H6 molecular formula

F. Molecular Formula 1. Find the empirical formula. 2. Find the empirical formula mass. 3. Divide the molecular mass by the empirical mass. 4. Multiply each subscript by the answer from step 3.

F. Molecular Formula The empirical formula for ethylene is CH2. Find the molecular formula if the molecular mass is 28.1 g/mol? empirical mass = 14.03 g/mol 28.1 g/mol 14.03 g/mol =

G. Hydrates Compounds with a certain number of water molecules attached MgSO4·7H20 = magnesium sulfate heptahydrate Use a prefix to indicate number of water molecules MgSO4 without water is called anhydrous

G. Hydrates To determine the number of water molecules, find the mole ratio of the anhydrous compound to the water Find the moles of each Set up a ratio: moles water/moles salt Whole number answer is the number that goes in front of H2O

G. Hydrates A 5g sample of a hydrate of Cu(NO3)2 was heated, and only 3.9g of the anhydrous salt remained. What is the formula and name of the hydrate? Step 1: determine moles of the salt and the water 3.9g Cu(NO3)2 x 1mole = 0.02mol Cu(NO3)2 5g-3.9g=1.1g water 1.1gH2O x 1mole = .06mol H2O 18.02g

Step 2: determine ratio Step 3: formula and name Moles H2O/moles Cu(NO3)2 0.06 mol H2O/0.02 mol Cu(NO3)2 = Step 3: formula and name Cu(NO3)2·3H2O Copper (II) nitrate trihydrate