Do-now- work with partners  Let’s say your group has been put in charge of making breakfast for this class. You get to decide what everybody eats. Make a shopping list of 10 items you are going to need, with the amounts listed as well. ItemAmount

Chapter 10 Chemical Quantities

Objectives  10.1a Convert among the count, mass and volume of something.  10.1b Explain how chemists count the number of atoms, molecules, or formula units in a substance.  10.1c Determine the molar mass of an element and of a compound  10.2a Describe how to convert the mass of a substance to the number of moles of a substance, and moles to mass.

How to measure… Apples?  What are some ways that you could measure 12 apples?  By counting: there are 12, or one dozen apples  By mass: there are about 2 kg of apples  By volume: there are about 0.2 bushels (a unit of volume)  You can set up conversion factors knowing these!

Considering all of this  If I have 90 apples, how many kg of apples do I have?  Roughly 15 kg of apples

The chemistry mole

Moles  A mole (mol) is 6.02 x representative particles of a substance and the SI unit for amount of a substance  “Representative particles”- atoms, molecules, formula units  6.02 x : also known as Avogadro’s number  The mole allows chemists to count the number of representative particles in a substance

Conversion using moles OR

Practice  How many molecules are in 2.00 moles of glucose, C 6 H 12 O 6 ?  1.20 x molecules  How many atoms of carbon are in 2.00 moles of glucose?  7.22 x atoms C

Molar Mass  Remember atomic mass?  The atomic mass of an element is actually the same as the mass of a mole of an element  Also called molar mass.  That means that 12 g of Carbon has the same amount of atoms as 16 g of Oxygen!  Measured in g or g/mol

What is the molar mass of…  Copper?  63.5 g in 1 mol  Nitrogen?  14 g in 1 mol

Lets look at some moles

The mass of a mole of a compound  We said that representative units can be not just elements, but also formula units and molecules  To calculate the molar mass of a compound, find the number of grams of each element  For example, what is the molar mass of hexane, C 3 H 8 ?  3 Carbon atoms- 3 x g/mol = g/mol  8 Hydrogen atoms- 8 x 1.01 g/mol = 8.08 g/mol  = g/mol

Practice  Lets try to find the molar mass for each of these compounds and elements

Mole-mass relationship  The molar mass of a substance can be used to convert between the moles of a substance and the mass of a substance  Conversion factors:  This makes it possible to know exactly how many moles are in a substance!

So… Mass Moles Particles Moles Divide by molar mass Multiply by molar mass Divide by Avogadro’s constant Multiply by Avogadro’s constant

Homework  Read  P. 338 # 60-62, 65  Lab Tomorrow!  Quiz Friday  Test in one week! (Wednesday)

Do-now  Find the molar mass of: H 2 O 2 Lead (IV) Chromate

Molar volume at STP  According to Amadeo Avogadro’s Hypothesis, equal volumes of gases at the same temperature and pressure contain the same number of particles.  The molar volume of a gas is 22.4 L/1 mol of gas at STP  STP (Standard Temperature and Pressure)- 0 º C and 1 atmosphere

Practice  At STP, what volume is occupied by 6.7 mol of H 2 ?  1.5 x 10 2 L

10.3

Objective  10.3a Calculate the percent composition of a compound.

Composition of the human body

Percent composition  Percent Composition is the percent by mass of each element in a compound.

How to calculate percent composition  The percent composition of an element in a compound is the mass of the element divided by the mass of the compound

Practice problem  What is the percent composition of the compound when 2.72 g of potassium reacts with 2.48 grams of chlorine to form 5.20 g of potassium chloride?  (52.4% K, 47.6% Cl)

Using molar mass  Molar Mass can also be used to calculate the percent composition of a compound

Practice  HgO  92.6% H, 7.39 % O  Ag 2 O  93.1 % Ag, 6.90 % O

Homework  Lesson Check 10.2 questions  P , questions  Quiz tomorrow

Objectives  10.3b Calculate the empirical formula of a compound.  10.3c Distinguish between empirical and molecular formulas.

Empirical Formula  The empirical formula of a compound gives the lowest whole-number ratio of atoms or moles of the elements in a compound.  For example: the empirical formula for N 2 O 4 is NO 2.  Compounds can have different molecular formulas, but the same empirical formulas C2H2C2H2 C 2 H 2 C8H8C8H8 C 8 H 8

Calculating Empirical Formulas  You can calculate empirical formulas with percent composition!  Lets say we have a compound that is 25.9% N and 74.1% O 1. Change % into grams 2. Convert grams to moles 3. Divide all values by smallest moles 4. Determine empirical formula  The empirical formula is N 2 O 5

Find the empirical formulas!  36.1% Ca, 63.9% Cl  40.0% C, 6.7% H, 53.3% O

Do-now  Find the empirical formula of a compound that is 40.0% sulfur and 60.0% oxygen?

Determining Molecular formulas  The molecular formula is a whole number multiple of the empirical formula  A compound of Carbon and Hydrogen has the empirical formula C 3 H 7 and the molar mass 86 g. What is its molecular formula?  C 6 H 14

Homework  Lesson Check, p. 333  Labs are due Tuesday!  Quiz Monday  Test Wednesday

Do-now  Find the percent composition for the following:  CuO  AgNO 3  H 2 O Extra Credit: Put the answers on the board! Extra Credit: Put the answers on the board!

Objectives  10.2b Convert the volume of a gas at STP to the number of moles of a gas.  10.3c Distinguish between empirical and molecular formulas.

Conversion Problems  What is the mass of 2.00 moles of propane gas, C 3 H 8 ?  88.0 grams  What volume would be occupied by 2.00 moles of propane gas, C 3 H 8, at standard conditions?  44.8 liters

More conversion problems  How many moles of Hydrogen (H 2 ) molecules are present in 9.0 x molecules of hydrogen?  1.5 moles  What is the volume, in liters, occupied by 1.5 x atoms of argon gas (Ar) at STP?  5.6 liters

Homework  Complete lab sheets for Penny lab and Magnesium Lab  Study for Chapter 10 test (Friday!)