Kiss My Molar Mass Chapter 4, Section 2

Concept Review Matter can be measured by counting (moles) or by weighing something (mass). The Mole: Is the basic measuring unit of atoms/molecules. It’s like a counting unit (like a dozen eggs!) Avagodro’s Number= 6.022 x 10 ^23

The mole Is also associated with a mass. The mass of 1 mole of an element is equal to the atomic mass of the element in grams. 1 mole of Copper (Cu) = 6.022 x 10^23 Cu atoms = 63.55 g (Atomic Mass#)

The size of a mole is equal to... -A mole of grains of rice would cover all the land in the world to a depth of 75 meters! -a mole of hockey pucks is roughly equal to the mass of the moon! -A mole of baseballs would just about fit perfectly into a ball bag the size of the Earth!

How many moles? For elements: 1 mole of element = 6.022 x 10^23 atoms of element = X g, where X = Atomic Mass. For compounds; 1 mole of compound = 6.022 X 10^23 molecules of compound= Y g, where Y Molar Mass Element/Comound Formula Fomula Mass (no Units) Molar Mass (grams/mole) Atomic Hydrogen H 1.01 1.01 g/mol Molecular Hydrogen H2 2.02 2.02 g/mol Carbon Dioxide CO2 1(12.01) +2(16.00) 44.01 g/mol Water H2O 2(1.01)+1 (16.00) 18.02 g.mol

Finding the molar mass... Page 127 #8: Determine the molar mass of each of the following elements: Manganese, Mn c. arsenic, As Cadmium, Cd d. Strontium, Sr Molar Mass = The mass in grams of one mole of a substance *1 mole of carbon-12 atoms has a mass of 12.00 g, so the molar mass of carbon-12 is 12.00 g/mol

Using Molar Mass: grams-to moles Converting moles of a substance to mass in grams: moles x molar mass Example: How many moles are in 23 grams of gold? Step 1: Go to the periodic table and find the atomic mass of gold? Atomic Mass of Au= 196.97 g/mol Step 2: Convert from grams to moles: (23 g Au) (1 mole/196.97 g) = 0.117 mol Au Notice that the units of grams cancel!

Practice: Using Molar Mass: grams-to moles Page 127 #15 and #16 -How many moles does 11 g of silicon, Si, contain? Step 1: Go to the periodic table and find the atomic mass. AM of Si= 28.09 g/mol Converting moles of a substance to mass in grams: moles x molar mass Step 2: Convert from grams to moles: (11 g of Si) (1 mole/28.09g/mol) = 0.391 mol *grams cancel out!

Practice: Using Molar Mass: grams-to moles #16 How many moles does 205 g of helium, He, contain? Step 1: Go to the periodic table and find the atomic mass. Step 2: Convert from grams to moles: Converting moles of a substance to mass in grams: moles x molar mass

Using Molar Mass: moles-to grams Moles x (molar mass of element)/ 1 mol of element Example: What is the mass of 54.5 mol of water? Step 1: Go to the periodic table and calculate the molar mass of water: MM H2O = 2(1.01)+1(16.00)= 18.02 g/mol Step 2: Convert from moles to grams: (54.5 mol H2O)(18.02 g/1 mol)=982 g water Moles cancel out!

Practice:Using Molar Mass: moles-to grams Page 127 #13 What is the mass in grams of 0.48 mol of platinum, Pt? Step 1: Go to the periodic table and calculate the molar mass: MM = 195.08 g/mol Step 2: Convert from moles to grams: Moles x (molar mass of element)/ 1 mol of element (0.48 mol Pt)(195.08 g/mol) = 93.64 *moles cancel out!

Practice:Using Molar Mass: moles-to grams Page 127 #14: What is the mass in grams of 3.1 mol of mercury, Hg? Step 1: Go to the periodic table and calculate the molar mass: Step 2: Convert from moles to grams: Moles x (molar mass of element)/ 1 mol of element

Your Turn Using Molar Mass: grams-to moles Problems 1,3,5,7 Using Molar Mass: moles-to grams Problems 2,4,6,8