 # Topic Three The Mole Gram Formula Mass l

• Slides: 31 Topic Three The Mole Gram Formula Mass l The same as formula mass, except expressed in grams instead of atomic mass. l It is common to express the gram formula masses of molecular substances as gram molecular mass. Gram Formula Mass & Percent Composition - Hydrates l Crystals that contain attached water molecules are called hydrates. n When determining gram formula mass or percentage of water, treat the water molecule as a single unit. l Substances without water attached are termed anhydrous. Sample Problem l Determine the percent by mass of water in sodium sulfate decahydrate. l Discuss experimental technique Chemistry Lab Popcorn Lab Chemistry Lab Composition of a Hydrate The Mole l Is a specific number of particles (either atoms or molecules, etc) l A mole is defined as the number of atoms of carbon present in 12. 000 grams of C-12. l The number of particles in a mole of a substance is 6. 022 x 1023. The Mole l The mass of one mole of a substance can be found by determining its gram formula mass. l The gram formula mass of any substance is the mass of one mole of that substance. Let’s Practice l How many grams of sodium sulfate would we need to have one mole of sodium sulfate? Let’s Practice Some More l Activity (“Who Wants To Be a Mole- ionaire”) n With a partner, I want you to obtain one mole of water and one mole of sodium chloride, and one mole of table sugar (C 12 H 22 O 11) n Hint: density of water is 1 g/ml Chemistry Humor l Two atoms are walking down the street. l Says one atom to the other, "Hey! I think I lost an electron!" l The other says, "Are you sure? ? " l "Yes, I'm positive!" Chemistry Humor l Why did the white bear dissolve when it jumped in the water? l Because it was a polar bear! Converting Moles To Grams l What if I asked you to get half a mole of water? How much would you get? l Grams= # of moles x (gram form mass / 1 mole) Converting Moles To Grams l. How many grams are present in 4 mol of sodium iodide (Na. I)? Converting Grams To Moles l Suppose I had a bag of pre-1982 pennies, but didn’t know how many pennies were in the bag. I know how much the whole bag weighs, and I know that each penny weighs 3. 1 grams. Can I figure out how many pennies are in the bag? How? Converting Grams To Moles l It’s the same idea converting grams to moles! l # moles = number of grams / gram form mass Let’s Practice l How many moles are equivalent to 12 grams of HCl (hydrochloric acid)? Practice l Review Book Page 40 n #’s 30, 35 Chemistry Humor l Why does hamburger have lower energy than steak? l Because it's in the ground state. Types of Formulas l Empirical l Molecular Empirical Formulas l An empirical formula represents the simplest integer ratio in which atoms combine to form a compound. l Ionic formulas are always empirical formulas. n Ionic substances don’t form discrete units n They are an array of ions Molecular Formulas l Covalently bonded substances form discrete units that we call molecules. l Sometimes the empirical formula represents the simplest ratio, but also the actual ratio. n Water Molecular Formulas l Other times the molecular formula may be a multiple of the empirical formula. l Example: Glucose l Molecular formula C 6 H 12 O 6 l Empirical formula CH 2 O Let’s Practice l Rev Book Page 24 l #’s 8, 10, 11, 12, 13 (tough one), 14 Finding Molecular Formulas From Empirical Formulas l If we know the molecular mass and the empirical formula, we can figure out the molecular formula. l Example: Rev Bk Page 41 #40 Let’s Practice l #41 -43 (page 41) Chemistry Humor l Why are chemists great for solving problems? l They have all the solutions. Mole Relations In Balanced Equations l The relative amounts (by number of particles) of reactants and products are given by the coefficients. l Coefficients represent both the basic unit and the mole ratios in balanced equations. l Mole ratios can be determined from the coefficients Mole Relations In Balanced Equations Let’s look at the balanced chemical equation 4 NH 3 + 5 O 2 4 NO + 6 H 2 O Practice Problem l How many moles of oxygen would we need to completely react with 2 moles of NH 3 according to the previous balance reaction? l If the above reaction took place, how many moles of water would be produced? How many grams of water would be produced? Let’s Practice l Rev Bk Page 42, #44