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Chapter 6 Chemical Composition. Counting by Weighing Counting is time consuming Weighing is fast If we know average mass, we can count by weighing.

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Presentation on theme: "Chapter 6 Chemical Composition. Counting by Weighing Counting is time consuming Weighing is fast If we know average mass, we can count by weighing."— Presentation transcript:

1 Chapter 6 Chemical Composition

2 Counting by Weighing Counting is time consuming Weighing is fast If we know average mass, we can count by weighing

3 Counting by Weighing Plain M&Ms

4 Counting by Weighing Peanut M&Ms

5 Calc Plain M&Ms Actual Plain M&Ms Calc Peanut M&M Actual Peanut M&Ms Calc Mini M&Ms Actual Mini M&Ms Lab 1 Lab 2 Lab 3 Lab 4 Lab 5 Lab 6 Lab 7 Lab 8

6 Atom are small Really small Gold Atomic Force Microscope (AFM) that can simultaneously map surface topography and measure the "dragging" or frictional force of the tip as it scans across a surface.

7 Atomic Masses: Counting by Weighing Atomic Mass Units  amu Only used for atoms Very Small!! 1 amu = 1.66 x g Mass number units on periodic table: amu 1 atom

8 Atomic Masses: Counting by Weighing We need a reasonable number to weigh atoms Avogadro ( ) Avogadro's Hypothesis: equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. He also proposed that oxygen gas and hydrogen gas were diatomic molecules.

9 Avogadro’s Number x The Mole

10 Mole Facts 6.02 X Watermelon Seeds: Would be found inside a melon slightly larger than the moon X Donut Holes: Would cover the earth and be 5 miles (8 km) deep X Pennies: Would make at least 7 stacks that would reach the moon.

11 Mole Facts 6.02 X Grains of Sand: Would be more than all of the sand on Miami Beach X Blood Cells: Would be more than the total number of blood cells found in every human on earth X C0 2 Molecules: Would be found in 1 Mole Balloon TM at STP. 1 Liter bottle of Water contains 55.5 moles H 2 0

12 Mole Facts 5 Pound Bag of Sugar contains 6.6 moles of C 12 H 22 O 11 1 Mole Balloon TM : Contains 22.4 Liters of any gas at STP. There are 3 types of moles that live underground in North America: Eastern Mole, Hairy-Tailed Mole and Star-Nosed Mole The "Mexican" Mole: Is a chocolate sauce or turkey stew. It comes from the Aztec word "molli." For recipes go to Web Hangouts.

13 grams  moles  molecules

14 Molar Mass A chemical compound is a collection of atoms Molar mass is the mass in grams of one mole of a chemical compound To find molar mass, add up the masses of all the atoms

15 Figure 6.3: Various numbers of methane molecules.

16 Molar Mass of Sulfur dioxide Sulfur dioxide = SO 2 1 mole SO 2  1 mole S atoms  2 moles O atoms 1 mole S atoms = 1 X g = g 2 moles O atoms = 2 X g = g 1 mole SO 2 molecules = g/mol Don’t round molar mass

17 Molar Mass of PVC PVC is polyvinyl chloride, C 2 H 3 Cl What is the mass of 1 mole C 2 H 3 Cl? 2 mol C atoms = 2 x = g 3 mol H atoms = 3 x = g 1 mol Cl atoms = 1 x = g = g/mol Don’t round molar mass

18 Calculate Molar Mass Sodium nitride, Na 3 N Carbon disulfide, CS 2 Ammonium bromide, NH 4 Br Ethyl alcohol, C 2 H 5 OH g/mol Na 3 N g/mol CS g/mol NH 4 Br g/mol C 2 H 5 OH

19 Calculating Mass from Moles What is the mass of 4.86 mol of CaCO 3 ? Molar Mass of CaCO 3 ? 1 mol Ca = 1 x g = g 1 mol C = 1 x g = g 3 mol O = 3 x g = g Molar mass of CaCO 3 = g/mol

20 Calculating Mass from Moles Molar mass of CaCO 3 = g What is the mass of 4.86 mol of CaCO 3 ? 4.86 mol CaCO 3 x g = ? mol = 486 g CaCO 3

21 Moles from Mass How many moles is 1.56 g of juglone? Juglone is a dye used for centuries that produced from black walnut trees. It is also a natural herbicide. Formula = C 10 H 6 O 3 Find Molar Mass of juglone g/mole

22 Moles from Mass 1mol = g of juglone 1.56 g juglone x 1 mol juglone =? g mol juglone 8.96 x mol juglone

23

24 Percent Composition of Compounds Percent by mass Percent = x 100% Mass fraction of a given = element PartWhole Mass of element present in 1 mol of compound Mass of 1 mol of compound

25 Percent by Mass of Each Element in PVC, C 2 H 3 Cl % C = x 100% = % C % H = x 100% = 4.84 % H % Cl = x 100% = % Cl g g g g g g % Total to check 2 mol C atoms = 2 x = g 3 mol H atoms = 3 x = g 1 mol Cl atoms = 1 x = g = g/mol

26 grams  moles  molecules

27 Percent by Mass Price Number of Cookies/Package E.L. Fudge original $ Famous Amos Vanilla $ Dunksters Double Crème $ Value Time Peanut Butter $2.0954

28 Mole Day, March 20, 2008 Celebrated annually on October 23 from 6:02 a.m. to 6:02 p.m., Mole Day commemorates Avogadro's Number (6.02 x ), which is a basic measuring unit in chemistry. For second term, we are celebrating on March 20th. Mole Day was created as a way to foster interest in chemistry. Schools throughout the United States and around the world celebrate Mole Day with various activities related to chemistry and/or moles.

29 Mole Day, March 20, 2008 For a given molecule, one mole is a mass (in grams) whose number is equal to the atomic mass of the molecule. For example, the water molecule has an atomic mass of 18, therefore one mole of water weighs 18 grams. An atom of neon has an atomic mass of 20, therefore one mole of neon weighs 20 grams. In general, one mole of any substance contains Avogadro's Number of molecules or atoms of that substance. This relationship was first discovered by Amedeo Avogadro ( ) and he received credit for this after his death.

30 Extra Credit Mole Day Projects Make Mole Day treats to share: Moleasses cookies, Avogadro Dip, Mole Cake, Guacamole or Taco-mole sauce Make an object of “mole” art Create a “Moletin” Board or poster Write a Mole Day poem or song to perform for the class Create a “Mole-opoly” game Create mole day flag or costume Create a mole day T-shirt (5-points maximum) Make a mole piñata or a stuffed mole

31 Extra Credit Mole Day Projects 0 to 20 points extra credit are possible. Points given will be based on effort and creativity and added to your homework grade. You may do more than one project BUT you may receive a maximum of 20 points. There is no make-up or late projects allowed.

32 grams  moles  molecules

33 Figure 6.5: Ball-and-stick model of P 4 O 10.

34 Empirical Formula of a Compound Converting masses measured in laboratory to chemical formulas Need to convert gram to moles and then develop an empirical formula Empirical Formula – the formula of a compound that expresses the smallest whole- number ratio of the atoms present. Molecular Formula – the actual formula of the compound.

35 Determining the Empirical Formula of a Compound (p. 179) Step 1 - Obtain the mass of each element Consider g of the compound % Cu = g Cu 14.94% N = g N 51.18% O = g O

36 Determining the Empirical Formula of a Compound (p. 179) Step 2 - Determine the number of moles of each element g Cu x = mol Cu g N x = mol N g O x = mol O 1 mole g 1 mole g 1 mole g

37 Determining the Empirical Formula of a Compound (p. 179) Step 3 - Divide the number of moles of each element by the smallest number of moles to convert the smallest number to

38 Determining the Empirical Formula of a Compound (p. 179) Step 3 continued - If all the number are integers (whole numbers), they are the subscripts in the empirical formula. If one or more of these numbers are not integers, go to Step 4. The empirical formula is CuN 2 O 6 [i.e., Cu(NO 3 ) 2 ]

39 Determining the Empirical Formula of a Compound (p. 179) Step 4 – Multiply the numbers you derived in step 3 by the smallest number that will convert all of them to whole numbers. This set of numbers represents the subscripts in the empirical formula.

40 Empirical Formula of a Compound C 6 H 12 O 6 = CH 2 O C 6 H 6 = CH Na 2 O 2 = NaO


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