Aim: How to calculate Percent Composition DO NOW: What is the number of moles of potassium chloride present in 148 g? What is the molar mass of CuSO4 5H2O? What is the mass of 3.01 x 1023 atoms of carbon? How to Calculate % Composition

Percent Composition The percent composition is the mass percentage of each type of atom (element) in a compound. % mass of element = 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑 x 100% How to Calculate % Composition

Percent Composition from Mass Data Percent composition can be calculated from experimental data. A student prepares a compound of tungsten chloride from 3.946 g of tungsten and 3.806 g of chlorine. Calculate the percent composition. % W = 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑊 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑊 𝐶𝑙 2 x 100% = 3.946 𝑔 7.752 x 100% = 50.9 % % Cl = 𝑚𝑎𝑠𝑠 𝑜𝑓 𝐶𝑙 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑊 𝐶𝑙 2 x 100% = 3.806 𝑔 7.752 x 100% = 49.1 % How to Calculate % Composition

Percent Composition from Chemical Formula % mass = 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 𝑖𝑛 1 𝑚𝑜𝑙 𝑜𝑓 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑 𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑 x 100% How to Calculate % Composition

Percent Composition from Chemical Formula To calculate the percent composition of a component in a compound: Find the molar mass of the compound by adding up the masses of each atom in the compound. Calculate the molar mass of the component in the compound for which you are solving. Divide the molar mass of the component by the total molar mass of the compound and multiply by 100 How to Calculate % Composition

Percent Composition from Chemical Formula Step1 8C + 10H +4N + 2O (8 x 12.0 g/mol) + (10 x 1.0 g/mol) + ( 4 x 14.0 g/mol) + (2 x 16.0 g/mol) = 194.0 g/mol How to Calculate % Composition

Carbon: 8 𝑥 12.0 𝑔/𝑚𝑜𝑙 194 𝑔/𝑚𝑜𝑙 x 100% = 49.5 % Step 2 Carbon: 8 𝑥 12.0 𝑔/𝑚𝑜𝑙 194 𝑔/𝑚𝑜𝑙 x 100% = 49.5 % Hydrogen: 10 𝑥 1.0 𝑔/𝑚𝑜𝑙 194 𝑔/𝑚𝑜𝑙 x 100% =5.1 % Nitrogen: 4 𝑥 14.0 𝑔/𝑚𝑜𝑙 194 𝑔/𝑚𝑜𝑙 x 100% = 28.9 % Oxygen: 100% - (49.5 + 5.1 + 28.9) = 16.5 % How to Calculate % Composition

Percent Composition of Crystal Hydrates A HYDRATE is a CRYSTALLINE compound in which ions are attached to one or more WATER molecules. Example: Na2CO3 10H2O  Notice how WATER molecules are BUILT INTO the chemical formula  Substances without water built into the formula are called ANHYDRATES. How to Calculate % Composition

Problem: What is the percentage by mass of water in sodium carbonate crystals (Na2CO3 10H2O)? Step 1: Calculate the formula mass for the hydrate. Na = 2 x 23.0 g/ mol = 46. 0 g/mol C = 1 x 12.0 g/mol = 12.0 g/mol O = 3 x 16. 0 g/mol = 48.0 g/mol H2O = 10 x 18.0 g/mol = 180 g/mol Formula mass of hydrate = 286 g/mol How to Calculate % Composition

Step 2: Set up and Calculate % composition by mass = mass of part/ mass of whole X 100% % H2O by mass =(180 g/mol)/(286 g/mol) x 100% % H2O by mass = 62.9 % How to Calculate % Composition

Percent Composition as a conversion Factor http://wps.prenhall.com/wps/media/objects/477/488597/le0602.html We can use mass percent composition as a conversion factor between grams of an element and grams of the compound. The mass percent composition of sodium in sodium chloride is 39%. This can be written as: 39 g of Sodium : 100 g of Sodium Chloride How to Calculate % Composition

This can be written in fractional form: These fractions are conversion factors between grams of Na and grams of NaCl. How to Calculate % Composition

The FDA recommends that adults consume less than 2 The FDA recommends that adults consume less than 2.4 g of sodium per day. How many grams of sodium chloride can you consume and still be within the FDA guidelines? Sodium chloride is 39% sodium by mass. Known Unknown 2.4 g Na grams of NaCl 39 g Na : 100 g NaCl 2.4 g Na x 100 𝑔 𝑁𝑎𝐶𝑙 39 𝑔 𝑁𝑎 = 6.2 g NaCl How to Calculate % Composition

Practice Problems A 45.9 g sample of copper, Cu, combined with oxygen to give 51.69 g of an oxide compound. The percent composition of this compound is: 88.8 % Cu, 11.2% O 24.4% Cu, 75.6% O 60.1% Cu, 39.9 % O 11.3% Cu, 88.7% O How to Calculate % Composition

2. Calculate the percent compost ion of each set: H2O H=___11 2. Calculate the percent compost ion of each set: H2O H=___11.1%_____ O=______88.9%______ H2O2 H = ____5.88%____ O =_______94.1%_____ How to Calculate % Composition

3. How many grams of sodium will combine with 567 3. How many grams of sodium will combine with 567.0 g of Sulfur from Na2S? (Hint: use % composition as conversion factor) 815.6 g How to Calculate % Composition