MOLES!!!! I. Counting Atoms. II.Composition and Formulas for Compounds. A. Atomic Masses. B. Moles. C. Molar Mass. A. Percent Composition
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1 Chapter 8 1 I MOLES!!!! I. Counting Atoms A. Atomic Masses A day without chemistry is like a day without the Sun!! B. Moles C. Molar Mass II.Composition and Formulas for Compounds A. Percent Composition B. Calculating Empirical Formulas C. Calculating Molecular/Ionic Formulas
2 I. Counting Atoms Candy and Other Small Things 2 Chemistry 6 Criteria Air Pollutants (EPA) CO Pb NO 2 O 3 P.M. SO 2
3 A. Atomic Masses Isotopes and Atomic Mass Units Isotopes atoms with same atomic # but different mass # s Sulfur three naturally occurring isotopes 32 S, 33 S, 34 S Need average mass of sulfur atom Sulfur isotope Mass (g) 32 S 33 S 3 34 S x10-23 g x10-23 g x10-23 g Natural Abundance 95% 4% 1% 100 atom sample x10 g x10 avg mass = 100 atoms = x10-23 g / atom g x g
4 Example If I obtain a sample of 89 argon atoms, what is the mass in amu? 4 B. Moles Need Mole a # of atoms that provides an easily measurable mass # of atoms that provides an easily measurable mass
5 The Mole Atomic Mass mass of 1 atom (amu) 5 Molar Mass mass of 1 mole of atoms (g)
6 Mole Cont d 6 Element C Mg Rn Mass of 1 atom (amu) Mass of 6.022x10 23 atoms (g) Conversion factors
7 Calculations with the Mole 1. If I have g of Cu how many moles of Cu do I have? 7 How many Cu atoms do I have? 2. If I have 6.25x10 24 atoms of Ar, what is the mass of my sample of Ar?
8 C. Molar Mass What is the mass of 1 molecule of Methane? CH 4 8 What is the mass of 1 mole of methane molecules? What is the molar mass of Fe(ClO 2 ) 2?
9 Compound 1 Molecule (# Atoms) 1 Mole (# Moles of atoms) 9 Mass (Amu) Molar Mass(g) C 2 H 6 Ca 3 (PO 4 ) 2
10 4. How many moles of C 2 H 6 are in a g sample of C 2 H 6? 10 How many molecules of C 2 H 6 are in the sample?
11 Who, me? What is the mass (g) of butanoic acid (C 4 H 8 O 2 ) contained in a 2.35x10 22 molecule sample of butanoic acid?
12 6. How many Cl atoms are in a 2.54 g sample of CCl 4? A sample of H 2 S contains 6.65x10 23 H atoms. What is the mass of the sample of H 2 S?
13 II. Experimentally Determining the Composition and Formulas for Compounds 13 A. Calculating Percent Composition Percent Example Score 94 out of 106 is that an A? Percent Part Whole 94 points 106 points x100% x100% % Mass Percent in Chemical Compounds
14 8.The chemical formula for Kryptonite has been proposed to be Na 3 Li 3 B 2 (Si 2 O 7 ) 2 (OH)F. What is the percent by mass of oxygen in Kryptonite? 14
15 B. Calculating Empirical Formulas 15 Goal Experimentally Determine Formula for Chemical Compounds Types of Chemical Formulas 1. Molecular Formula (M.F.) - formula of an actual molecule 2. Empirical Formula (E.F.) - provides relative numbers of atoms in a molecule - subscripts are reduced to the smalles whole number ratios
16 How do we Calculate Empirical Formulas? 1. Determine the mass of each element present in the compound Convert mass to number of moles present for each atom. 3. Find the smallest ratio of each atom to all of the other atoms.
17 17 How do we Calculate Empirical Formulas? Cont d Calculated E.F. Multip. Factor New E.F. Other Sub. Use C 1 H C 2 H 3 (0.5, 1.5, 2.5, etc) C 1 H C 3 H 4 (0.33, 1.33, etc) C 1 H C 4 H 5 (0.25, 1.25, etc) C 1 H C 3 H 5 (0.66, 1.66, etc) C 1 H C 4 H 7 (0.75, 1.75, etc)
18 Example 9. If a g sample of copper metal is heated in a chlorine gas atmosphere, the mass of copper (I or II?) chloride produced is g. Calculate the empirical formula of the copper chloride. 18
19 10. Putrescine, an incredibly foul smelling compound that is generated during the decomposition of flesh, contains nitrogen, hydrogen, and carbon. During his quest to obtain the Ring and help Sauron conquer Middle Earth, Saruman the White, a magician and master chemist, tried to synthesize putrescine and use it as a weapon against the inhabitants of Middle Earth. In order to obtain the chemical formula of putrescine, Saruman analyzed a sample of putrescine and found it contained % N and % C. What is the empirical formula for putrescine? 19 Saruman, you stink!
20 Obtaining Empirical Formulas from Mass % 1. Determine the mass% and mass of each element present in the compound Convert mass to number of moles present for each atom. 3. Find the smallest ratio of each atom to all of the other atoms.
21 C. Calculating Molecular/Ionic Formulas from Empirical Formulas How many sticks of gum in a pack of gum? 21
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Chapter 8 1 I MOLES!!!! I. Counting Atoms A. Atomic Masses A day without chemistry is like a day without the Sun!! B. Moles C. Molar Mass II.Composition and Formulas for Compounds A. Percent Composition
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