The Math of Chemistry FactorLabel Method the Mole

The Math of Chemistry Factor-Label Method the Mole gram formula weight Avogadro Number Scientific Notation Percent Composition Empirical Formulas Hydrates

Begin working on HW 11 and 12 • To convert units, you must write down what you know, then use a conversion factor to convert it to what you want to know. 0. 32 g = ______mg use 1000 mg = 1 g 0. 32 g 1000 mg 1 g = 32 mg

What if you only know a similar conversion factor, not the exact one you need? 3 3 • 0. 436 m = _______cm – use 1 m = 100 cm; then cube both sides. – 13 m 3 = (100)3 cm 3 – 1 m 3 = 1, 000 cm 3 0. 436 m 3 100000 cm 3 1 m 3 This procedure is called the factor label method 436000 cm 3 or 4. 36 x 105 cm 3 =

Use page 29 in your book to help you do problem 28 page 196 • On the blackboard, three students can earn a free homework pass by correctly solving and carefully explaining how to do #28 a and b OR #28 f or g

Quiz: Factor Label Method convert the following: 1. 30 cm = ______m 1 2. 3600 sec =____hours 3. 10 cm 3 = _____ m 3 30 cm (1 m) (100 cm) = 0. 30 m 3600 sec (1 min)(1 hour) (60 sec)(60 min) 10 cm 3 (13 m 3) = 0. 01 m 3 (1003 cm 3)

Molecular and Formula Mass • Instead of usingle atoms with masses on the order of 10 -24 g, we use moles – one mole = 1 Avogadro number of particles – 6. 02 x 1023 particles = 1 Avogadro number. • We can use the numbers on the periodic table as either atomic mass units or grams. When we use them as amu we are talking about quantities too small to measure. • When we use moles, we are talking about 6. 02 x 1023 atoms or ions or formula units or molecules.

Find the gfw of cyclopentane C 5 H 10 55 CC = 5(12. 0 amu) 10 10 HH = 10 (1. 00 amu) 5(12. 0) + 10 (1. 00) = 60. 0 + 10. 0 = 70. 0 amu or g/mole

27 amu 14 amu Find the gfw of Al. N • First, identify the elements, and how many 1 Al and 1 N of each are in the compound. • Then find the atomic masses on the periodic table • Then, multiply how many of an atom by how much it weighs. 1(27. 0) and 1(14. 0) • Finally, find the sum of all the pieces of the compound. 1(27. 0) + 1(14. 0) 41. 0 g

In Groups • You are responsible for finding the gram formula masses of each compound on the sheet of paper. Points will be awarded for the groups who have successfully calculated the greatest number of gfw. • Students will come up to the board to explain how they found the gfw of a substance. Points will be awarded for the quality of the explanation.

Quiz: Find the gfw for the following compounds… 1. Na. Cl 2. Al 2 S 3 3. Ca 3(PO 4)2 1. 23 + 35 = 58 g/mole 2. 2(27) + 3(32) = 54 + 96 = 150 3. 3(40) + 2(31) + 8(16) = 120 + 62 + 128 = 310 g/mole