X Chemistry Unit 8 The Mole Problem Solving involving Chemical Compounds

Vocab: Percent composition – mass of the part divided by mass of the whole times 100 Empirical Formula – the simplest whole number ratio of atoms in a compound Molecular Formula- the true whole number ratio of atoms in a compound

Vocab: Molar Mass- the mass of 1 mole of a substance  Equal to the atomic mass for elements  For a compound, the sum of the atomic masses for all the atoms in a compound  Units = grams/mole = g/mol Mole - the amount of substance that is equal to 6.02x10 23 particles of that substance

Vocab: Representative particle- the smallest particle of a substance; defined by the type of substance:  Element = atom  Covalent compound = molecule  Ionic compound = formula unit  Charged atom = ion

Vocab: Avogadro’s Number- the number of particles in 1 mole of any substance  Avogadro’s # = 6.02x10 23 Molar Volume- the volume of 1 mole of ANY gas at STP (Standard Temperature and Pressure = 0°C and 1atm),  22.4 Liters

What is a Mole? Amedeo Avogadro (Italian Mathematician)  used Carbon as the basis for the masses of the other elements  devised a counting relationship between grams and moles  1 mole = 6.02x10 23 atoms of any element  1 mole of carbon = 12.0 g Carbon (matches the atomic mass on the P.T.)

What is a Mole? (REAL WORLD EXAMPLE) Relationships:  1 dozen = 12 donuts just like 1 mole = 6.02x10 23 atoms BUT:  1 dozen feathers = grams and  1 dozen bricks = 32,400 grams!

What is a Mole?  The mass of 1 mole of any element will be different than 1 mole of any other element Practice:  What are the masses of 1 mole of the following elements? Magnesium =  g/mol Nitrogen =  g/mol

One-mole Amounts

Determining Molar Mass: Steps in Solving:  Write the element symbols in the formula down the left hand side of the paper  Multiply the number of atoms by the molar mass of that element according to the P.T. and rounded to the tenths place  Sum the products from step 2  the units on your final answer are g/mol (grams per mole)

Determining Molar Mass: Examples:  CO 2  (NH 4 ) 2 SO 4

Mole Conversions Moles! Mass Representative particles (atoms, molecules, formula units, ions) Mole Conversions Use molar mass Use Avogadro’s # (6.02 x )

Converting between Moles and Grams: Mole-Mass Conversions  Dimensional Analysis!! Use molar mass as conversion factor! Moles to grams:  # of molesmolar mass (g) = # of grams 1 mole Grams to moles:  # of grams1 mole = # of moles Molar mass (g)

Converting between Moles and Grams: Examples: How many moles of CCl 4 are their in 523.4g?

Converting between Moles and Grams : Examples: (cont.) How many grams of Na are there in 12.3 moles of Na?

Conversions Between Moles & Particles: Use Avogadro’s Number!! Examples: How many atoms of carbon are contained in moles of C?

Conversions Between Moles & Particles Examples: How many molecules of sodium chloride are contained in moles of NaCl?

Conversions Between Moles & Particles Challenge!! How many molecules of barium chloride are contained in 1.07 grams of barium chloride?

Percent Composition Problems: 2 types: 1. Using data measured in grams to find percentage of element in some given sample (More specific) 2. Using a chemical formula to find percentage of each element in a compound (More general)

Percent Composition Problems: Type 1: (just like the separation lab!)  % of element in a specific sample

Percent Composition Problems: Examples: If g of sodium combines completely with g of chlorine to form a compound, what is the % composition of each element in this compound?

Percent Composition Problems: Type 2:  Mass of element in 1 mole of a compound

Percent Composition Problems: Example: What is the percent composition of each element in C 12 H 22 O 11 ?

Empirical Formula Calculations Percent to mass Mass to moles Divide by Small Multiply ‘til whole %  g  moles empirical formula Divide by smallest mole value

Multiply ‘til Whole Hints Common Possible Endings:.33 x 3.25 x 4.67 x 3.50 x 2

Determining the Empirical Formula of a Compound: Steps for Solving: Convert grams of each element to moles using molar mass Inspect your answers and find the smallest number of moles of all the answers Divide each number of moles for each element by the smallest determined in step 2  Your answers to step 3 have no units since it was moles/moles they cancel out!! IF the ratios do not come out to a whole number, multiply all values by some whole number to get all whole numbers These numbers are the subscripts for each of the elements in the empirical formula

Example: Find the empirical formula for a compound composed of 78% iron and 22% oxygen. Determining the Empirical Formula of a Compound:

A compound is 81.1 % boron and 18.9% hydrogen. What is the empirical formula of this compound?

Determining the Molecular Formula of a Compound: Steps for Solving:  Find the Empirical Formula  Find the molar mass of the Empirical Formula  Divide the Molecular molar mass by the Empirical molar mass  The answer to step 3 is the factor you multiply each subscript in the Empirical Formula by to get the Molecular Formula

Determining the Molecular Formula of a Compound: A compound of B and H is 81.10% B and 18.9% H. Its empirical formula is B 2 H 5. What is its molecular formula if the molar mass of the compound is 53.3 g/mol?