Unit 7: The Mole Chapter 11 Test: Friday, December 19, 2008

Counting Matter What are some common ways we count matter? 1. Dozen = Ream = Score = Mole = 6.02 x 10 23

The Mole It represents a counted number of things. In chemistry the term mole represents the number of particles in a substance. It is NOT this furry little animal or the spot on your face…

The Mole  The mole (6.02 x ) is called Avogadro’s number  Q: Why would chemists use moles instead of dozens when referring to atoms, molecules, etc?  A: These particles are so small, it takes a lot of them to make an amount we can see and use. Written in expanded form: 602,000,000,000,000,000,000,000

The Mole 1 dozen cookies = 12 cookies 1 mole of cookies = 6.02 X cookies 1 dozen cars = 12 cars 1 mole of cars = 6.02 X cars 1 dozen Al atoms = 12 Al atoms 1 mole of Al atoms = 6.02 X atoms ***Mole is abbreviated “mol”

A Mole of Particles A particle is a general word we use to refer to atoms (neutral), ions (charged), molecules (covalently bonded), and formula units (ionically bonded). 1 mole C = 6.02 x carbon atoms 1 mole of K + = 6.02 x potassium ions 1 mole H 2 O = 6.02 x water molecules 1 mole NaCl = 6.02 x sodium chloride formula units

1 mole is equal to: (Of gas at STP)

Calculations with Particles 6.02 x particles = 1 mole Example - How many molecules are in 3.00 moles of N 2 ? 3.00 mol N x molecules = 3.00 mol N x molecules = 1 mol N 2 Example - How many moles of Na are in 1.10 x atoms? 1.10 x atoms Na 1 mol Na= 1.10 x atoms Na 1 mol Na= 6.02 x atoms Na 6.02 x atoms Na

1. How many atoms in mole of Al? 2. How many moles of S in 1.8 x S atoms Practice particle calculations

The Mole  How do chemists “count” Avogadro’s number?  By measuring mass (just like how they count aluminum cans for recycling)

Molar Mass of Atoms The mass (think grams) of one mole of a substance Atomic masses of atoms are relative masses based on the mass of carbon-12 One mole of carbon contains 6.02 x atoms of carbon One mole of carbon contains 6.02 x atoms of carbon 1 carbon atom is amu 1 mole of carbon is grams (aka g/mol of carbon)

The mass of 1 mole (in grams) Equal to the numerical value of the average atomic mass (get from periodic table) Examples: Examples: 1 mole of C atoms= 12.0 g 1 mole of Mg atoms =24.3 g 1 mole of Cu atoms =63.5 g Molar Mass of Atoms

Find the molar mass Practice molar mass of atoms 1.1 mole of Au atoms = 2. 1 mole of Sn atoms =

Mass in grams of 1 mole equal to the sum of the atomic masses Example: What is the mass of 1 mole of CaCl 2 ? 1 mole Ca x 40.1 g/mol = 40.1 g Ca 1 mole Ca x 40.1 g/mol = 40.1 g Ca 2 moles Cl x 35.5 g/mol = g Cl 2 moles Cl x 35.5 g/mol = g Cl g/mol CaCl g/mol CaCl 2 Molar Mass of Molecules and Formula Units

Practice molar mass of compounds Prozac, C 17 H 18 F 3 NO, is a widely used anti- depressant that inhibits the uptake of serotonin by the brain. Find its molar mass.

Calculations with Molar Mass Examples 1.How many grams are in 2 moles of Cu? 2 moles of Cu g of Cu = 1 mole of Cu 1 mole of Cu 2.How many moles are in 100 g of H 2 O? 100 g of H 2 O 1 mole of H 2 O = g of H 2 O g of H 2 O

The artificial sweetener aspartame (C 14 H 18 N 2 O 5 ), commonly known as Nutra-Sweet, is used to sweeten diet foods, coffee and soft drinks. How many moles of aspartame are present in 225 g of aspartame? The artificial sweetener aspartame (C 14 H 18 N 2 O 5 ), commonly known as Nutra-Sweet, is used to sweeten diet foods, coffee and soft drinks. How many moles of aspartame are present in 225 g of aspartame? Practice calculations with molar mass

Examples 1.How many grams of CO 2 are present in 3 molecules of CO 2 ? 3 molecules of CO 2 1 mole of CO g of CO 2 = 6.02 x molecules of CO 2 1 mole of CO 2 2.How many formula units are present in 12.0 grams of NaCl? 12.0 g of NaCl 1 mole of NaCl 6.02 x formula units of NaCl = g of NaCl1 mole of NaCl Calculations with Particles/Mass

Examples 1.How many L of CO 2 at STP are present in 300 molecules of CO 2 ? 300 molecules of CO 2 1 mole of CO L of CO 2 = 6.02 x molecules of CO 2 1 mole of CO x molecules of CO 2 1 mole of CO L of O 2 gas at STP would contain how many molecules of O 2 ? 56.2 L of O 2 1 mole of O x molecules of O 2 = 22.4 L of O 2 1 mole of O 2 Calculations with Volume

Practice calculations with particles/mass Diabetics do not properly regulate insulin, which tells the body to take up glucose from the blood. What is the mass of 1.20 x molecules of glucose (C 6 H 12 O 6 )?

Extra step - Diatomic Molecules Example: How many atoms of O are present in 78.1 g of oxygen? 78.1 g O 2 1 mol O X molecules O 2 2 atoms O 32.0 g O 2 1 mol O 2 1 molecule O 2Practice: How many grams of Cl are present in 100 atoms of chlorine?

Percent Composition Percentage by mass of each element in a compound The percent comp. is found by using the following formula:

% Composition What is the percent of each element in sodium sulfite, Na 2 SO 3 ? 2 mole Na x g/mol Na = g Na 1 mole S x g/mol S = g S 3 moles O x g/mol O = g O g gSodium 2 moles Na x g/mol Na = g Na % = ( g / g) x 100 = % Na Sulfur 1 mole S x g/mol S = g S % = ( g / g) x 100 = % S Oxygen 3 moles O x g/mol O = g O % = ( g / g) x 100 = % O Molar Mass of Na 2 SO 3 = % % % %

Glutamic acid ( C 5 H 8 NO 4 ) is used to flavor foods and tenderize meat (it is also a component of MSG – monosodium glutamate). What is the percent carbon in C 5 H 8 NO 4 ? Practice % composition

Empirical Formulas This is the LOWEST whole number ratio of the elements in a compound. For example, the empirical formula for C 6 H 6 is CH What is the empirical formula for each? C 2 H 6 C 2 H 6 C 6 H 12 O 6 C 6 H 12 O 6

Calculating Empirical Formula To calculate the empirical formula, given the mass or percent of elements in compound, follow these steps: If given a percent sign, remove the sign & change to grams. You are assuming you have 100 g of the compound. Convert the grams to moles. Decide which number of moles is the lowest, then divide each number of moles by this number. If the number divides out evenly, these are the subscripts of the elements in the compound. If any of the numbers have a.5, multiply them all by two & then place these numbers as the subscripts.

Calculating Empirical Formula Find the empirical formula for a compound containing 18.8% nickel and 81.2% iodine. Nickel 18.8 g Ni / g/mol Ni = mol Ni Iodine 81.2 g I / g/mol I = mol I Ni = 0.320/0.320 = 1 I = 0.640/0.320 = 2 The formula is = NiI 2 LOWEST

Practice Empirical Formula Find the empirical formula given 65.2% Sc and 34.8 % O

Molecular Formulas These are many multiples of the empirical formula. Represents the actual formula (ex: glucose is C 6 H 12 O 6 ). 1.Determine the empirical formula 2.Find the empirical formula mass (you are given the molecular formula mass) 3.Divide the molar mass for the molecular formula by the molar mass of the empirical formula 4.Compare it to the molecular mass to determine the number of multiples.

Calculating Molecular Formula Example: The molecular mass of the compound Sc 2 O 3 (previous problem) is 414 g/mol. What is the molecular formula? Empirical Formula = Sc 2 O 3 Empirical Formula Mass = 2 mol Sc x g/mol Sc = g Sc 3 mol O x g/mol O = g O molar mass = g Sc 2 O 3 molar mass = g Sc 2 O 3 Find the ratio… 414 g / g = 3 (meaning molecular formula is 3 times larger than empirical formula) Molecular Formula = Sc 6 O 9

Practice Molecular Formula A molecule has 85.6% carbon and 14.5% hydrogen. If the molecule has a mass of 42.1 grams, what is the molecular formula? A molecule has 85.6% carbon and 14.5% hydrogen. If the molecule has a mass of 42.1 grams, what is the molecular formula?