How do you measure? Often measure something by one of three different methods- by counting by mass by volume
How about them apples By count: 1 dozen = 12 apples By mass: 1 dozen = 2.0 kg of apples By volume: 1 dozen = 0.2 bushels To do this you must use conversion factors
Practice Problems If 0.20 bushel is 1 dozen apples & a dozen apples has a mass of 2.0 kg, what is the mass of 0.50 bushel of apples? Assume 2.0 kg of apples is 1 dozen and that each apple has 8 seeds. How many apple seeds are in 14 kg of apples?
What is a mole? 6.02 x10 23 also known as Avogadro’s number 602,000,000,000,000,000,000,000 Considers the very small size of atoms Helps with the conversion of units
But What is a Mole??? 6.02x10 23 representative particles are in each and every mole SI unit of measuring the amount of a substance
Representative particle Atoms Molecules Formula units A mole of any substance contains Avogadro’s number of representative particles
Converting Number of particles to moles Equation This equation can be placed in a unit conversion to find the number of particles
Practice Problem Magnesium is a light metal used in the manufacture of aircraft, automobile wheels, tools and garden furniture. How many moles of magnesium is 1.25 * 10 23 atoms of magnesium?
Converting Moles to Number of Particles Determining how many atoms are in one mole of a compound This number is discovered from the formula:
Molecules and Atoms How many moles are in one CO 2 molecule? A mole of CO 2 of contains 1 Avogadro’s number of carbon dioxide molecules However, there are 3 atoms in every 1 molecule of carbon dioxide So, there are 3 moles worth of atoms in every 1 moles worth of carbon dioxide molecules
Converting Moles to Number of Particles To find the number of atoms, molecules, representative particles in a mole of a compound, you must first determine the number of representative particles, then you can use the following equation
Practice Problems Propane is a gas used for cooking & heating. How many atoms are in 2.12 mole of propane (C 3 H 8 )?
The mass of a mole of an element The atomic mass of a single atom is expressed as atomic mass units Atomic mass units is the atomic mass expressed in grams What is the atomic mass of krypton?
Pop Quiz What is the molar mass of oxygen? What is the molar mass of carbon? What is the molar mass of hydrogen?
Molar Mass To calculate the molar mass of a compound: Find the number of grams of each element in one mole of the compound. Then add the masses of the elements in the compound Applies to ionic & molecular compounds Ex: Carbon Dioxide (CO 2 ) 44 g/mol
Finding Molar Mass of Sulfur Trioxide Determine how many atoms of each element are in the compound Add up the masses of all the atoms
The Mole-Volume Relationship Avagadro’s hypothesis: Equal volumes of gases at the same temperature and pressure contain equal number of particles Change in temperature or pressure will change the volume Figure 10.9 In each container, the volume occupied by the gas molecules is small compared with the container ﾕ s volume, so the molecules are not tightly packed. a. The molecules in this container are small. b. This container can accommodate the same number of larger molecules.
Standard Temperature & Pressure (STP) We usually measure volume at STP Temperature: 0 o C Pressure: 101.3 kPa or 1 atm At STP, 1 mol or 6.02x10 23 rep particles, of any gas occupies a volume of 22.4L 22.4L = molar Volume
Calculating Volume at STP Molar volume can be used to convert the known number of moles to the volume of a gas at STP
Percent Composition from the Chemical Formula If you know the formula you can calculate the percent composition using the following Figure 10.14 The percent composition of water is always the same regardless of the volume of the water sample. A sample of water is always 11.1% H and 88.9% O by mass.
Percent Composition as a Conversion Factor Use percent composition to calculate the number of grams of any element in a specific mass of a compound Multiply mass of compound by a conversion factor based on the percent composition
Practice Problem How much C & H are in 82.0 g of propane You found that propane is 81.8% C and 18% H. That means that in a 100-g sample of propane, you would have 81.8 g of C and 18 g of H. You can use the ratio to calculate the mass of carbon contained in 82.0 g of propane (C 3 H 8 ).
Empirical Formula Lowest whole number ratio of the atoms of the elements in a compound Example: H 2 O 2 or Hydrogen Peroxide The ratio is 1:1 even though there are two atoms of each element in the compound
Calculating Empirical Formula Convert your percent and express as moles Convert from grams to moles using your mole ratio Divide each by the lower number of moles