Name: ______________________ Percent Composition Date: ______________Period:___ Introduction: What is your shirt or sweater made of? Check your tag, and list the “ingredients” and amounts of those components below. You have a bag containing a total of 200 M&M’s. There are 23 green M&M’s, 50 red M&M’s, 60 blue M&M’s, 44 yellow, and 23 brown M&M’s. What is the percentage of green M&M’s in the bag? Write word equations for how you would determine this information in the space below. This concept can also be applied to determining the percentage of a compound that is made of a certain element. Write a word equation that would explain what you did above. How could this be applied to determining the amount of an element in a compound . Percent Composition – The percent composition of a component in a compound is the percent of the total mass of the compound that is due to that component. The definition in your textbook is the percent by mass of each material found in an item (substance). There are different types of problems involving percent composition: ‐
‐
‐
Calculating percent composition from mass data. Calculating percent composition from a chemical formula. Using percent composition as a conversion factor. It will be imperative that you determine which type of problem first before beginning the problem. Let’s apply this concept! Name: ______________________ Date: ______________Period:___ % composition = Percent Composition 100 Don’t forget your units and labels!! Example 1: Find the percent composition of copper (Cu) in CuBr2. 1. Determine what information you have and what you will need. (Which type of percent composition problem is this?) KNOWN: UNKNOWN: 2. Determine any information needed to solve the problem that can be calculated from the information given. 3. Use the % composition equation used earlier to solve for the last unknown. Example 2: When a 13.60 g sample of a compound containing only magnesium and oxygen is decomposed, 5.40 g of oxygen is obtained. What is the percent composition of this compound? 1. Determine what information you have and what you will need. (Which type of percent composition problem is this?) KNOWN: UNKNOWN: Name: ______________________ Date: ______________Period:___ Percent Composition 2. Determine any information needed to solve the problem that can be calculated from the information given. 3. Use the % composition equation used earlier to solve for the last unknown. Example 3: Propane, (C3H8), the fuel commonly used in gas grills, is one of the lighter compounds obtained from petroleum. Calculate the percent composition of propane. 1. Determine what information you have and what you will need. (Which type of percent composition problem is this?) KNOWN: UNKNOWN: 2. Determine any information needed to solve the problem that can be calculated from the information given. 3. Use the % composition equation used earlier to solve for the last unknown. Name: ______________________ Date: ______________Period:___ Percent Composition Example 4: Using an earlier sample problem containing propane, we found that a 100g sample of propane would contain 81.8g of Carbon and 18 g of hydrogen. The ratio would be 81.8g C/100g propane. We can use this ratio to determine how much carbon is in 82.0g of propane. 1. Determine what information you have and what you will need. (Which type of percent composition problem is this?) KNOWN: UNKNOWN: 2. Determine any information needed to solve the problem that can be calculated from the information given. 3. Determine what # you should start with, correctly set‐up the conversion factor, and solve. You must use dimensional analysis! Practice: Remember to use the steps above. 1. A compound is formed when 9.03 g of Mg combines completely with 3.48 g of N. What is the percent composition of this compound? Name: ______________________ Date: ______________Period:___ 2. Calculate the percent nitrogen in these common fertilizers. a) NH4NO3 b) NH3 Percent Composition 3. Find the percent metal (by mass) in each compound: a) Ag2S b) Al2O3 c) CaCO3 Extension Problems (These are great types of questions I would expect you to be able to analyze and complete on the test.) 1. Suppose you have the choice to either mine ore that is 20% chalcocite (Cu2S) or ore that is 30% chalcopyrite (CuFeS2). Assuming all other factors are equal, which would you choose? Support your answer with calculations. Name: ______________________ Percent Composition Date: ______________Period:___ 2. Two common iron‐containing minerals are hematite (Fe2O3) and magnetite (Fe3O4). If you had the same mass of each, which sample would contain the larger mass of iron? Support your answers with calculations. 3. Chromium minerals are found at three different mine sites in these forms: a. Site 1: Chromite, FeCr2O4 b. Site 2: Crocoite, PbCrO4 c. Site 3: Chrome ochre, Cr2O3 Based only on percent composition, at which site is chromium mining most feasible? Support your answers with calculations.