The Mole Chemistry’s Unit of Convenience

Calling particles by the right name Particles of a type of a(n)… are called…  ion……………………  element………………..  diatomic compounds….  covalent compound……  ionic compound………. ions atoms molecules formula units (f.u.) molecules

Revisiting Chemical Reactions  A typical synthesis reaction: Mg + O 2  MgO  now balance it… What does this mean? * Two _____ of Mg react with one ________ of O 2 to produce two ___________ of MgO 22 atomsmolecule formula units

Ratios in Chemical reactions The chemicals involved in this reaction some together in a specific ratio: 2 Mg + O 2  2 MgO 2 : 1 : 2 The ratio comes from the coefficients. What if I “doubled” the “recipe”--what would the equation mean then? 4 atoms : 2 molecule : 4 formula units

Those are not convenient amounts!  Atoms are so small that it is hard to work with chemical equations on the atomic scale.  If I did the recipe 12 times over, then the ratio would be from 2 : 1 : 2 to 24 atoms : 12 molecules : 24 f.u.  Simplifying in “dozens:” 2 doz atoms : 1 doz molec : 2 doz f.u.

Convenient units… like dozen  “Dozen” is convenient because we all know that “one doz = 12” of whatever…  In chemistry we have a convenient unit called the MOLE. 1 mol = 6.02 x particles In other words: 1 mol =

Mole Facts  One mole of rice grains is more than all the rice that has been grown since the beginning of time!  One mole of hockey pucks would be equal in mass to the mass of the moon!  Assuming the human body has 60 trillion cells (6 X ) and there are 6 billion people (6 X 10 9 ) on earth, the total number of human cells on earth is about ½ a mole!

Things to know:  The mole is a constant number.  The number for the mole is also called Avogadro’s number.  Factoring comes in handy when dealing with the mole!  Conversion factors: Conversion factors:

Practice (using factoring!):  How many atoms are in 5 moles of Lithium?  How many molecules are in 4.5 moles of chlorine gas?  How many f.u. are in 6 mol of potassium chloride?  How many moles are there in 5.66 X atoms of neon?  How many moles are there in X formula units of sodium iodide?  How many moles are there in 4.6 X molecules of carbon tetrachloride?

Back to the Equation: 2 Mg + O 2  2 MgO This can be interpreted several ways-- 2 atoms Mg : 1 molec O 2 : 2 f.u. MgO 2 doz of atoms Mg : 1 doz of molec O 2 : 2 doz of f.u. MgO 2 mol of atoms Mg : 1 mol of molec O 2 : 2 mol of f.u. MgO MOST SIMPLY PUT: 2 mol Mg : 1 mol O 2 : 2 mol MgO

More examples: 2 H 2 + O 2  2 H 2 O 6 CO H 2 O  C 6 H 12 O O 2 CH O 2  CO H 2 O H 2 + Cl 2  2HCl

How is this helpful?  The mole is connected to the Periodic Table! “The mass of one mole of atoms of a pure element in grams is numerically equal to the atomic weight of that element in amu. This is also called the “molar mass.” The SI unit is g/ mol.  We already know the molar mass of EVERYTHING in Chemistry! Atomic mass: amu :: molar mass : grams

How is this helpful? = Atomic mass of Mg: = Therefore, the molar mass Mg: 24 amu 24 g = I can’t say, “go get 2 atoms of Mg…” = But I CAN say, “go get 2 mol Mg” because I know that 1 mol of Mg = 24 g Mg

More practice with molar mass:  Find the molar mass of the following: Cu = Ca = Au = Na = Pb = C = He = Xe = 63.5 g/mol g/mol g/mol 4.0 g/mol 40.1 g/mol 23.0 g/mol 12.0 g/mol g/mol

Those were all elements...  If I have one mol oxygen gas, how can I know the molar mass?  Oxygen gas = O 2 [remember diatomic!] n One mol O 2 = two mol O atoms n molar mass O = 16 g n molar mass O 2 = 2(16g) = 32.0 g

Molar Mass of Molecules n Find the molar mass of these molecules: H 2 = CO = O 2 = CO 2 = N 2 = CH 4 = Cl 2 = NH 3 = 2.0 g/mol 32.0 g/mol 28.0 g/mol 71.0 g/mol 28.0 g/mol 44.0 g/mol 16.0 g/mol 17.0 g/mol

Try these chemical compounds: = CaCl 2 = [one mol Ca + two mol Cl] = Al 2( SO 4 ) 3 = 2 ( Al) + 3 ( S) + 12 ( O) = 1(40.1 g) + 2(35.5 g) = g 27.0 g 32.1 g 16.0 g 54.0 g g g = g/mol

For an extra challenge: n “TNT” [C 7 H 5 (NO 2 ) 3 ] 7 (12 g C) = 5 (1.0 g H) = 3 (14.0 g N) = 6 (16.0 g O) = 84.0 g 5.0 g 42.0 g 96.0 g g; TNT is 227 g/mol

Molar mass as a conversion factor The molar mass is a connection between g and molg and mol n What is the mass in grams of 3.5 mol of copper? n What is the mass in grams of 7 moles of PbSO 4 ? n How many moles are there in 38 g of Mg? n How many moles are there in 339 g of KCl?

Another mole conversion factor 1 mol of a gas = 22.4 STP STP = Standard Temperature and Pressure Now you can convert moles into particles, grams, and liters.liters How many moles are in 47 L of hydrogen gas at STP? If I have 4.5 moles of oxygen gas at STP, how many Liters do I have? How many moles are in 100 L of methane?

Percent composition n Calculate the formula (or molar) mass n Calculate the formula mass for the element or elements in question n Divide the total mass of EACH element by the formula mass of the compound and multiply times 100. Examples: Find the percent comp for-- -Al 2 O 3 -HgO -Fe 2 O 3 -H 2 SO 4

Mole Road Map MOLES ParticlesGrams Liters