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” “U” stands for “unknown” Use the coefficient from the balanced equation

Mole-to-Mole Problems Ex-1: If you want to manufacture 150 moles of ammonia (NH 3 ), how many moles of hydrogen will you need? H 2 + N 2  NH 3 Step 1: Balance the equation 3H 2 + N 2  2NH 3

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

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

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

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

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

Mole-to-Mole Practice Ex-2: If you want to make 100 moles of ammonia (NH 3 ), how many moles of Nitrogen (N 2 ) will you need? 3H 2 + N 2  2NH 3 50 mol N 2

Mole-to-Mole Practice Ex-3: If you have 36 moles of nitrogen (N 2 ), how many moles of hydrogen (H 2 ) will you need? 3H 2 + N 2  2NH mol H 2

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

Gram-to-Gram Problems Ex-1: How many grams of glass (SiO 2 ) can be etched by 100 grams of hydrofluoric acid (HF)? HF + SiO 2  SiF 4 + H 2 O Step 1: Balance the equation 4HF + SiO 2  SiF 4 + 2H 2 O

Ex-1: How many grams of glass (SiO 2 ) can be etched by 100 grams of hydrofluoric acid (HF)? 4HF + SiO 2  SiF 4 + 2H 2 O Step 2: Identify the “given” and “unknown” from problem with units G: 100 g HF U: # g SiO 2

Ex-1: How many grams of glass (SiO 2 ) can be etched by 100 grams of hydrofluoric acid (HF)? 4HF + SiO 2  SiF 4 + 2H 2 O 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 g HF

Ex-1: How many grams of glass (SiO 2 ) can be etched by 100 grams of hydrofluoric acid (HF)? 4HF + SiO 2  SiF 4 + 2H 2 O 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 SiO g HF 4 mol HF

Ex-1: How many grams of glass (SiO 2 ) can be etched by 100 grams of hydrofluoric acid (HF)? 4HF + SiO 2  SiF 4 + 2H 2 O 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 SiO 2 x g SiO2 = g HF 4 mol HF 1 mol SiO2

Ex-1: How many grams of glass (SiO 2 ) can be etched by 100 grams of hydrofluoric acid (HF)? 4HF + SiO 2  SiF 4 + 2H 2 O 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 SiO 2 x g SiO 2 = g HF 4 mol HF 1 mol SiO 2 80 g SiO 2

Gram-to-Gram Practice Ex-2: How many grams of glass (SiO 2 ) can be made from 230 grams of H 2 O? 4HF + SiO 2  SiF 4 + 2H 2 O 380 g SiO 2

Ex-3: How many grams of Silicon fluoride (SiF 4 ) are needed to make g of water? 4HF + SiO 2  SiF 4 + 2H 2 O g SiF 4