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Aim: How to calculate Percent Composition  DO NOW: 1. What is the number of moles of potassium chloride present in 148 g? 2. What is the molar mass of.

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Presentation on theme: "Aim: How to calculate Percent Composition  DO NOW: 1. What is the number of moles of potassium chloride present in 148 g? 2. What is the molar mass of."— Presentation transcript:

1 Aim: How to calculate Percent Composition  DO NOW: 1. What is the number of moles of potassium chloride present in 148 g? 2. What is the molar mass of CuSO 4 5H 2 O? 3. What is the mass of 3.01 x atoms of carbon? How to Calculate % Composition

2 Percent Composition How to Calculate % Composition

3 Percent Composition from Mass Data How to Calculate % Composition

4 Percent Composition from Chemical Formula How to Calculate % Composition

5 Percent Composition from Chemical Formula To calculate the percent composition of a component in a compound: 1. Find the molar mass of the compound by adding up the masses of each atom in the compound. 2. Calculate the molar mass of the component in the compound for which you are solving. 3. Divide the molar mass of the component by the total molar mass of the compound and multiply by 100 How to Calculate % Composition

6 Percent Composition from Chemical Formula How to Calculate % Composition  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) = g/mol

7 How to Calculate % Composition

8 Percent Composition of Crystal Hydrates  A HYDRATE is a CRYSTALLINE compound in which ions are attached to one or more WATER molecules.  Example: Na 2 CO 3 10H 2 O  Notice how WATER molecules are BUILT INTO the chemical formula  Substances without water built into the formula are called ANHYDRATES. How to Calculate % Composition

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

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

11 Percent Composition as a conversion Factor   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

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13 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. How to Calculate % Composition

14 Practice Problems 1. A 45.9 g sample of copper, Cu, combined with oxygen to give g of an oxide compound. The percent composition of this compound is: a % Cu, 11.2% O b. 24.4% Cu, 75.6% O c. 60.1% Cu, 39.9 % O d. 11.3% Cu, 88.7% O How to Calculate % Composition

15 2. Calculate the percent compost ion of each set: H2OH2O H=___11.1%_____O=______88.9%______ H2O2H2O2 H = ____5.88%____O =_______94.1%_____ How to Calculate % Composition

16 3. How many grams of sodium will combine with g of Sulfur from Na 2 S? (Hint: use % composition as conversion factor) g How to Calculate % Composition


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