1. Practice Problem How many grams of sodium are present in 5.0 g of sodium hydroxide? % Na = Na NaOH X 100 22.98977 g/mol Na 39.997 g/mol NaOH X 100 = 57.5% Na 57.5% Na (5.0g NaOH) = 2.9 g Na 1 % Na = Step 1: Begin by finding the % sodium Step 2: Divide the portion you are looking for by the total formula times 100 Step 3: Substitute molar mass values into the expression Step 4: Calculate the % Step 5: multiply the % by the mass of sample to determine the mass of the portion. © Mr. D. Scott; CHS

2. Practice Problem How many grams of carbon are present in 9.0 g of carbon dioxide? % C = C CO 2 X 100 12.011 g/mol C 44.010 g/mol CO 2 X 100 = 27.3% C 27.3% Na (9.0g CO 2 ) = 2.5 g C 2 % C = Step 1: Begin by finding the % carbon Step 2: Divide the portion you are looking for by the total formula times 100 Step 3: Substitute molar mass values into the expression Step 4: Calculate the % Step 5: multiply the % by the mass of sample to determine the mass of the portion. © Mr. D. Scott; CHS

3. Practice Problem How many grams of magnesium are present in 12 g of magnesium sulfate? % Mg = Mg MgSO 4 X 100 24.305 g/mol Mg 120.368 g/mol MgSO 4 X 100 = 20.2% Mg 20.2% Mg (12g MgSO 4 ) = 2.4 g Mg 3 % Mg = Step 1: Begin by finding the % magnesium Step 2: Divide the portion you are looking for by the total formula times 100 Step 3: Substitute molar mass values into the expression Step 4: Calculate the % Step 5: multiply the % by the mass of sample to determine the mass of the portion. © Mr. D. Scott; CHS

4. Practice Problem How many grams of iron are present in 20. g of iron(II) nitrite? % Fe = Fe Fe(NO 2 ) 2 X 100 55.845 g/mol Fe 147.856 g/mol Fe(NO 2 ) 2 X 100 = 37.8% Fe 37.8% Fe x 20.g Fe(NO 2 ) 2 = 7.6 g Fe 4 % Fe = Step 1: Begin by finding the % iron Step 2: Divide the portion you are looking for by the total formula times 100 Step 3: Substitute molar mass values into the expression Step 4: Calculate the % Step 5: multiply the % by the mass of sample to determine the mass of the portion. © Mr. D. Scott; CHS

5. Practice Problem How many grams of lithium are present in 5.0 g of lithium phosphate? % Li = 3 x Li Li 3 PO 4 X 100 (3) 6.941 g/mol Li 115.794 g/mol Li 3 PO 4 X 100 = 18.0% Li 18.0% Li x 5.0.g Li 3 PO 4 = 0.90 g Li 5 % Li = Step 1: Begin by finding the % lithium Step 2: Divide the portion you are looking for by the total formula times 100 Step 3: Substitute molar mass values into the expression Step 4: Calculate the % Step 5: multiply the % by the mass of sample to determine the mass of the portion. © Mr. D. Scott; CHS

6. Practice Problem How many grams of mercury are present in 8.0 g of mercury(I) carbonate? % Hg = 2 x Hg Hg 2 CO 3 X 100 (2) 200.59 g/mol Hg 461.19 g/mol Hg 2 CO 3 X 100 = 87.0% Hg 87.0% Hg x 8.0g Hg 2 CO 3 = 7.0g Hg 6 % Hg = Step 1: Begin by finding the % mercury Step 2: Divide the portion you are looking for by the total formula times 100 Step 3: Substitute molar mass values into the expression Step 4: Calculate the % Step 5: multiply the % by the mass of sample to determine the mass of the portion. © Mr. D. Scott; CHS