1 / 26

Chemical Quantities

Chemical Quantities. Or How I Learned to Love the Mole. Conservation. What is the law of conservation of matter? In a chemical reaction, matter is neither created or destroyed. In other words molecules can be converted and decomposed but atoms are forever and are always fully accounted for.

halia
Download Presentation

Chemical Quantities

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chemical Quantities Or How I Learned to Love the Mole

  2. Conservation What is the law of conservation of matter? In a chemical reaction, matter is neither created or destroyed. In other words molecules can be converted and decomposed but atoms are forever and are always fully accounted for.

  3. Law of Conservation of Mass Conservation of Mass Video

  4. Balancing Equations Here are some links for balancing equations online Balancing Act Chem Balancer Also see Supplement 2C3(link) Please make a copy if you use this for practice. Place in handouts and activities folder.

  5. The Mole How do you measure matter? If it is something large like the number of beans in a bag, you just count them. If, however, it is something exceedingly small like an atom or ion, how do you count it? Counting individual particles is not possible, but you can “count” particles if you introduce a term that represents a specific number of particles. A “dozen” represents 12 of that item, and a mole represents 6.02 x 1023 representative particles of a substance.

  6. What is meant by “representative particles”? Representative particles are whatever you are talking about: atoms, molecules, or formula units (ions). The representative particle of most elements is the atom. Seven elements exist as diatomic molecules, and, as such, its representative particle is the molecule. The seven: H2, N2, O2, F2, Cl2, Br2, I2.

  7. Avogadro’s Numberyoutube link

  8. How much is a mole? A mole of pennies is very large.

  9. 1 mol representative particles 6.02 x 1023 particles • OK, so now we know that a mole is 6.02 x1023 representative particles. So how many atoms are in one mole of an compound, or how many moles are in 6.02 x 1023 atoms? • Example: • How many moles are in 6.02 x 1023 atoms of silver? • Solution: • Determine the conversion factor. • 1 mole = 6.02 x 1023 representative particles

  10. 1 mol Ag 6.02 x 1023 Ag atoms 6.02 x 1023 Ag atoms x

  11. 6.02 x 1023 molecules CO2 1 mole CO2 2 oxygen atoms 1 molecule CO2 x To find the number of atoms in a mole of a compound, you must determine the number of atoms in a representative formula of that compound. Example: How many oxygen atoms are in a mole of CO2? 1 mole CO2 x = 12.04 x 1023 atoms O2; or, 1.204 x 1024 atoms O2.

  12. When discussing the mole, using atoms leads to very large numbers. An easier way to discuss moles is to work with grams of atoms instead. The gram atomic mass (gam) is the atomic mass of an element expressed in grams. For carbon, the gam is 12.0 g. For atomic hydrogen, the gam is 1.0 g. What is the gam for iron and mercury? (55.85 g & 200.6 g) How many atoms are contained in the gram atomic mass of an element? The gam contains one mole of atoms (6.02 x 1023 atoms) of that element.

  13. Thus, if 12.0 g of carbon is the gam of carbon, 12.0 g is 1 mol of carbon, and has 6.02 x 1023 atoms. What is the mass of a mole of a compound? To answer this you must know the formula of the compound. The formula tells you the number of atoms of each element in a representative particle of that compound. You calculate the mass of a mole of a compound by adding together the atomic masses of the atoms making up the compound. This is called gram molecular mass (gmm) Example: What is the molecular mass of SO3?

  14. S (x1) = 32.1 g O (x3) = 16.0 g x 3 = 48.0 g SO3 = 80.1 g What is the gmm of H2O2? C2H6? PCl2? C3H7OH? N2O5? As you know, not all compounds are molecules. Sodium chloride (NaCl) is an ionic compound. Its representative particle is the formula unit. The mass of 1 mol of an ionic compound is the gram formula mass (gfm) As with gmm, you simply sum the atomic masses of the atoms in the compound.

  15. What is the gfm of ammonium carbonate, (figure out the formula yourself :) )? N (x2) = 14.0 g x 2 = 28.0 g H (x8) = 1.0 g x 8 = 8.0 g C (x1) = 12.0 g = 12.0 g O (x3) = 16.0 g x 3 = 48.0 g (NH4)2CO3 = 96.0 g Review: gam = mole of element gmm = a mole of molecules gfm = a mole of formula units (also generic for gmm) All of the above can be described by the generic term “molar mass”.

  16. 1 mole A gfm A x gfm B 1 mol B x Mole-Mass Relationships The gram formula mass of an element or compound is used to convert grams of a substance into moles grams A = mol A The gfm can also be used to convert moles of a substance into grams. mol B = grams B

  17. 76.0 gN2O3 1 molN2O3 x Example: How many grams are in 7.20 mol of N2O3? N2 = 28.0 g O3 = 48.0 g 1 mole N2O3 = 76.0 g 7.20 molN2O3 = 547.2 gN2O3 = 5.47 x 102 gN2O3 You Try It! 1. How many grams in .720 mol Be? 2. How many moles in 2.40 g N2? 6.48 g 0.086 mol

  18. Supplemental Work Here are links to a variety of supplements related to molar mass and molar relationships. Molar Mass Supplement 2C5 Molar Relationship Supplement 2C71 Molar Relationship Supplement 2C7II Please make a copy and place in handouts and activities folder.

  19. Percent Composition To keep your lawn healthy, wealthy, and wise you need to use fertilizer. You can’t just use any ol’ fertilizer. You need to use one that has the right mixture of elements or compounds depending on what you need to do. You need to know the relative amount of each nutrient. This is the same in the laboratory. When you make a new compound, you need to determine its formula by finding the relative amounts of elements in the compound. The relative amounts are expressed as the percent composition, the percent by mass of each element in a compound.

  20. grams of element X grams of compound There are as many percent values as there are elements in the compound. The percentages must add up to 100%. % mass of element X = x 100% Example: An 8.20-g piece of magnesium combines with a 5.40-g sample of oxygen completely to form a compound. What is the percent composition of this compound?

  21. mass Mg mass cmpd. 8.20 g 13.6 g = mass O mass cmpd. 5.40 g 13.6 g 1. Find mass of compound. 13.60 g = mass of compound (8.20 g + 5.40 g) 2. Find % of each element % Mg = = 60.3% % O = = = 39.7 %

  22. 36 g 44 g = 81.8 % 8 g 44 g = 18.2 % H Once you determine the percent composition of a compound you can determine the number of grams of an element in a specific amount of compound. Example: Calculate the mass of carbon in 82.0 g of propane, C3H8. 1. Determine % composition of C3H8. C3H8 = 44.0 g C: H:

  23. 81.8 g C 100 g C3H8 x 2. Use conversion factor based on percent by mass of carbon in ethane. a. 81.8 % C means that for every 100 g C3H8, 81.8 g will be C. 82 g C3H8 = 67.1 g C Check to see if 67.1/82 = 81.8 %

  24. Problems: Calculate the amount of hydrogen in: a. 350 g C2H6. b. 20.2 g NaHSO4 c. 124 g Ca(C2H3O2) 2 d. 378 g HCN e. 100 g H2O

  25. Homework Complete Supplement Unit 2 C5-Unit 2C10. This is all practice for you to understand the concepts discussed today.

More Related