Chemical Composition Chapter 8

Nutrasweet Aspartic acid Analysis Qualitative -- what elements -- C, H, N, & O. Quantitative -- how many of each element --C 4 H 7 NO 4.

Counting Atoms Atoms are too small to be seen or counted individually. Atoms can only be counted by weighing them. all jelly beans are not identical.all jelly beans are not identical. jelly beans have an average mass of 5 g.jelly beans have an average mass of 5 g. How could 1000 jelly beans be counted?How could 1000 jelly beans be counted?

Jelly Beans & Mints Mints have an average mass of 15 g. How would you count out 1000 mints? Why do 1000 mints have a mass greater than 1000 jelly beans?

Atomic Mass Unit Atoms are so tiny that the gram is much too large to be practical. The mass of a single carbon atom is 1.99 x g. The atomic mass unit (amu) is used for atoms and molecules.

AMU’s and Grams 1 amu = x g Conversion Factors x g/amu x amu/g

Calculating Mass Using AMU’S 1 N atom = amu (23 N atoms)(14.01 amu/1N atom) = amu

Calculating Number of Atoms from Mass 1 O atom = amu (288 amu)(1 O atom/16.00 amu) = 18 atoms O

Atomic Masses Elements occur in nature as mixtures of isotopes Carbon =98.89% 12 C 1.11% 13 C 1.11% 13 C <0.01% 14 C Carbon atomic mass = amu

AMU’s & Grams 1 atom C = amu = 1.99 x g 1 mol C = g Use TI-83 or TI-83 Plus to store x to A.

Measurements dozen = 12 gross = 12 dozen = 144 ream = 500 mole = x 10 23

The Mole The number equal to the number of carbon atoms in exactly 12 grams of pure 12 C. 1 mole of anything =  units of that thing that thing Equal moles of substances have equal numbers of atoms, molecules, ions, formula units, etc.

Figure 8.1 (a): All these sample of pure elements contain the same number (a mole) of atoms: x atoms Cu – 63.55gAg – 107.9g Pb – 207.2g

Figure 8.2: One- mole samples of iron (nails), iodine crystals, liquid mercury, and powdered sulfur How many atoms does each substance contain?

The Mole Substance Average Atomic Mass # Moles # Atoms (g) Na x Cu x S x Al x 10 23

Avogadro’s number equals  units

The Mole One mole of rice grains is more than the number of grains of all rice grown since the beginning of time!One mole of rice grains is more than the number of grains of all rice grown since the beginning of time! A mole of marshmallows would cover the U.S. to a depth of 600 miles!A mole of marshmallows would cover the U.S. to a depth of 600 miles! A mole of hockey pucks would be equal in mass to the moon.A mole of hockey pucks would be equal in mass to the moon.

Unit Cancellation How many dozen eggs would 36 eggs be? (36 eggs)(1 dozen eggs/12 eggs) = 3 dozen eggs How many eggs in 5 dozen? (5 dozen eggs)(12 eggs/1 dozen eggs) = 60 eggs

Calculating Moles & Number of Atoms 1 mol Co = g (5.00 x atoms Co)(1mol/6.022 x atoms) = 8.30 x mol Co (8.30 x mol)(58.93g/1 mol) = g Co Moles are the doorway grams moles atoms

Molar Mass A substance’s molar mass is the mass in grams of one mole of the compound. CO 2 = grams per mole 1 C = 1 ( g) = g 2 O = 2 ( g) = g g g

Calculating Mass from Moles CaCO 3 1 Ca = 1 (40.08 g) = g 1 C = 1 (12.01 g) = g 3 O = 3 (16.00 g) = g g g (4.86 molCaCO 3 )( g/1 mol) = 486 g CaCO 3

Calculating Moles from Mass Juglone 10 C = 10(12.01g) = g 6 H = 6(1.008 g) = g 3O = 3(16.00 g) = g g g (1.56 g juglone)(1 mol/174.1 g) = mol juglone

Percent Composition Mass percent of an element: For iron in iron (III) oxide, (Fe 2 O 3 )

% Composition CuSO 4. 5 H 2 O 1 Cu = 1 (63.55 g) = g 1 S = 1 (32.06 g) = g 4 O = 4 (16.00 g) = g 5 H 2 O = 5 (18.02 g) = g g g

% Composition (Continued) % Cu = g/249.71g (100 %) = % Cu % S = g/ g (100 %) = % S % O = g/ g (100 %) = % O % H 2 O = g/ g (100 %) = % H 2 O Check: Total percentages. Should be equal to 100 % plus or minus 0.01 %.

Formulas molecular formula = (empirical formula) x [x = integer] [x = integer] molecular formula = C 6 H 6 = (CH) 6 empirical formula = CH

Formulas Ionic compounds -- empirical formula NaCl NaCl CaCl 2 CaCl 2 Covalent compounds -- molecular formula - C 6 H 12 O 6 C2H6C2H6C2H6C2H6

Empirical Formula Determination 1.Base calculation on 100 grams of compound. 2.Determine moles of each element in 100 grams of compound. 3.Divide each value of moles by the smallest of the values. 4.Multiply each number by an integer to obtain all whole numbers (if necessary.)

Calculating Empirical Formulas % C, % N, 9.80 % H, & % O (63.68 g C)(1 mol/12.01g) = mol C/.8837 mol = 6 (12.38 g N)(1 mol/14.01g) = mol N/.8837 mol = 1 (9.80 g H)(1 mol/1.01 g) = 9.70 mol H/.8837 mol = 11 (14.14 g O)(1 mol/16.00g) =.8838 mol O/.8837 mol = 1 C 6 NH 11 O

Calculating Empirical Formulas g Al & g O (4.151 g Al)(1 mol/26.98 g) = mol Al/ mol = (3.692 g O)(1 mol/16.00 g) = mol O/ mol = Al (2) = 2 Al 1.5 O (2) = 3 O Al 2 O 3

Molecular Formulas % Cl, % C, & 4.07 % H (71.65g Cl)(1 mol/35.45g) = mol/2.021 mol = 1 (24.27 g C)(1 mol/12.01g) = mol/2.021 mol = 1 (4.07 g H )(1 mol/1.01g) = 4.03 mol/2.021 mol = 2 (EM) x = (MM) (49.46) x = (98.96) x = 2 x = 2 (EF) x = (MF) (ClCH 2 ) 2 = Cl 2 C 2 H 4