Section 3: Stoichiometry - Mole:Mole and Gram:Gram Unit 6: Stoichiometry Section 3: Stoichiometry - Mole:Mole and Gram:Gram

Stoichiometry Branch of chemistry that involves using known ratios of products and reactants to determine unknown data in a chemical reaction Chemists use stoichiometry conversions like cooks use cooking recipes Ratio for these conversions can be found in the balanced equation!! (Coefficients!)

Mole-to-Mole Formula When converting from moles of one substance to moles of another “G” stands for “given” chemical “U” stands for “unknown” chemical Use the coefficient from the balanced equation Use the coefficient from the balanced equation

Mole-to-Mole Problems Ex-1: If you want to manufacture 150 moles of ammonia (NH3), how many moles of hydrogen will you need? H2 + N2 → NH3 Step 1: Balance the equation 3H2 + N2 → 2NH3

Mole-to-Mole Problems Ex-1: If you want to manufacture 150 moles of ammonia (NH3), how many moles of hydrogen will you need? 3H2 + N2 → 2NH3 Step 2: Identify the “given” and “unknown” from the problem with units. G: 150 mol NH3 U: # mol H2

Mole-to-Mole Problems Ex-1: If you want to manufacture 150 moles of ammonia (NH3), how many moles of hydrogen will you need? 3H2 + N2 → 2NH3 G: 150 mol NH3 U: # mol H2 Step 3: Set up a conversion factor with given units in the bottom: 150 mol NH3 x _______ mol NH3

Mole-to-Mole Problems Ex-1: If you want to manufacture 150 moles of ammonia (NH3), how many moles of hydrogen will you need? 3H2 + N2 → 2NH3 G: 150 mol NH3 U: # mol H2 Step 4: The unit on top must be the unit you want; same as your “unknown” 150 mol NH3 x mol H2 mol NH3

Mole-to-Mole Problems Ex-1: If you want to manufacture 150 moles of ammonia (NH3), how many moles of hydrogen will you need? 3H2 + N2 → 2NH3 G: 150 mol NH3 U: # mol H2 Step 5: Plug in the coefficients from the balanced equation: 150 mol NH3 x 3 mol H2 = 225 mol H2 2 mol NH3

Mole-to-Mole Problems Ex-1: If you want to manufacture 150 moles of ammonia (NH3), how many moles of Hydrogen will you need? 3H2 + N2 → 2NH3 G: 150 mol NH3 U: # mol H2 Step 6: Round answer to the correct number of significant figures and include your unit!!!! 150 mol NH3 x 3 mol H2 = 225 mol H2 → 230 mol H2 2 mol NH3

Mole-to-Mole Practice Ex-2: If you want to make 100 moles of ammonia (NH3), how many moles of Nitrogen (N2) will you need? 3H2 + N2 → 2NH3 50 mol N2

Mole-to-Mole Practice Ex-3: If you have 36 moles of nitrogen (N2), how many moles of hydrogen (H2) will you need? 3H2 + N2 → 2NH3 110 mol H2

OMG ITS THE SAME AS THE MOLE TO MOLE FORMULA! Gram-to-Gram Formula Used to figure out the # of grams of one substance needed to make another “U” = “unknown”; “G” = “given” Use the coefficient from the balanced equation OMG ITS THE SAME AS THE MOLE TO MOLE FORMULA! Use the coefficient from the balanced equation

Gram-to-Gram Problems Ex-1: How many grams of glass (SiO2) can be etched by 100 grams of hydrofluoric acid (HF)? HF + SiO2 → SiF4 + H2O Step 1: Balance the equation 4HF + SiO2 → SiF4 + 2H2O

Gram-to-Gram Problems Ex-1: How many grams of glass (SiO2) can be etched by 100 grams of hydrofluoric acid (HF)? 4HF + SiO2 → SiF4 + 2H2O Step 2: Identify the “given” and “unknown” from problem with units G: 100 g HF U: # g SiO2

Gram-to-Gram Problems Ex-1: How many grams of glass (SiO2) can be etched by 100 grams of hydrofluoric acid (HF)? 4HF + SiO2 → SiF4 + 2H2O Step 3: Set up a conversion factor with the given units in the bottom… this will be its molar mass. The numerator will always be 1 mole of the “given” chemical 100 g HF x 1 mol HF 20.008 g HF

Gram-to-Gram Problems Ex-1: How many grams of glass (SiO2) can be etched by 100 grams of hydrofluoric acid (HF)? 4HF + SiO2 → SiF4 + 2H2O Step 4: Next, use a mole-to-mole conversion factor to go from one chemical to the other. Take the numbers for the coefficients from the balanced equation. 100 g HF x 1 mol HF x 1 mol SiO2 20.008 g HF 4 mol HF

Gram-to-Gram Problems Ex-1: How many grams of glass (SiO2) can be etched by 100 grams of hydrofluoric acid (HF)? 4HF + SiO2 → SiF4 + 2H2O Step 5: We need our answer in grams, so do a basic mole-to-gram conversion (1 mole on bottom; molar mass on top) 100 g HF x 1 mol HF x 1 mol SiO2 x 60.09 g SiO2 = 75.082 20.008 g HF 4 mol HF 1 mol SiO2

Gram-to-Gram Problems Ex-1: How many grams of glass (SiO2) can be etched by 100 grams of hydrofluoric acid (HF)? 4HF + SiO2 → SiF4 + 2H2O Step 6: Make sure your final answer is in the correct # of sig figs with its unit 100 g HF x 1 mol HF x 1 mol SiO2 x 60.083 g SiO2 = 75.082 20.0059 g HF 4 mol HF 1 mol SiO2 80 g SiO2

Gram-to-Gram Practice Ex-2: How many grams of glass (SiO2) can be made from 230 grams of H2O? 4HF + SiO2 → SiF4 + 2H2O 380 g SiO2

Gram-to-Gram Practice Ex-3: How many grams of Silicon fluoride (SiF4) are needed to make 100.50 g of water? 4HF + SiO2 → SiF4 + 2H2O 290.33 g SiF4