Warm up In the first FIVE minutes of class: Take out your prelab – set it on your desk. When the stapler arrives staple it to the front of today’s lab. READ through the purpose and background of today’s lab. Do number 1 of the prelab. Remember, we did problems like this in unit 1 

Pre lab 1. If your classroom has 13 girls and 12 boys, what percentage of the class are girls? Use the formula and show your work. Percent = (part/whole) x 100 Percent girls = (13/25) x 100 The class is 52% girls.

2. Use your text to define percent composition: The percent by mass of each element in a compound

Did you read the “READ THIS” on the pre lab Did you read the “READ THIS” on the pre lab? For example, to find the percent composition of sodium chloride, NaCl. Step 1: Find the mass of the whole compound. Sodium has a mass of 22.990 g/mol Chloride has a mass of 35.453 g/mol Mass of NaCl 58.443 g/mol

Step 2: Find the percent of each element in the whole Step 2: Find the percent of each element in the whole. Round to 2 decimal places. % Na = (mass of Na/mass of soNaCl) x 100 % Na = (22.990/58.443) x 100 % Na = 39.34 %

% Cl = (mass of Cl/mass of NaCl) x 100 % Cl = (35. 453/58 % Cl = (mass of Cl/mass of NaCl) x 100 % Cl = (35.453/58.443) x 100 % Cl = 60.66%

Find the percent composition of magnesium oxide Find the percent composition of magnesium oxide. Formula for magnesium oxide? MgO Step 1: Find the mass of the whole compound Mass Mg 24.305 g Mass O 15.999 g Mass MgO 40.304 g

Step 2: Find the percent of each element in the whole Step 2: Find the percent of each element in the whole. %Mg = (mass Mg/Mass MgO) x 100 %Mg = (24.305/40.304) x 100 %Mg = 60.30% %O = (mass O/Mass MgO) x 100 %O = (15.999/40.304) x 100 %O = 39.70%

A piece of iron weighing 11. 169 g is burned in air A piece of iron weighing 11.169 g is burned in air. The mass of the iron (III) oxide produced is 15.969 g. Use the law of conservation of mass to calculate the mass of oxygen that reacted with iron. Iron + oxygen  iron (III) oxide 11.169 g 15.969g So, mass oxygen? 15.969 – 11.169 = 4.800 g  

Iron + oxygen  iron (III) oxide 11.169 g 4.800 g 15.969g What is the percent of oxygen in the product? Remember… Percent = (part/whole) x 100 (4.800/15.969)x100 = 30.05% oxygen

Lab time!! #1 – Safety precautions! Crucible, lid and Mg ribbon are at the stations. Find other materials in the “not open slowly” drawer. During wait time – work on practice problems on your own paper Moving the crucible Hot looks like cold Don’t want to have to do lab over Al chairs tucked

Edits! #3 – Clean it gently with steel wool #7 – after #7, BEFORE #8 – Allow to COOL about 5 minutes. If you do not do this, you will loose a LOT of product (plus, its dangerous)

Practice problems: formula writing Aluminum chloride Sodium cyanide Nickel (III) sulfite Chromium (II) chloride Gold acetate Vanadium (V) oxide Lithium fluoride Lead (IV) ferrocyanide

Period 2 groups  Lab 1 Lab 6   Lab 2 Lab 7   Lab 3 Lab 8 

Closure Is the room clean? Are all 30 calculators back in the caddy? Are the goggles neatly put away?