The Mole. S We are familiar with using a specific term to represent a number of items in a group.

Transcription

1 Unit 5 The Mole S

2 The Mole S We are familiar with using a specific term to represent a number of items in a group. S 1 dozen = 12 units of something S 1 case of Cokes = 24 Cokes S In chemistry we use the term MOLE to indicate a collection of particles that = 6.02 x S 6.02 x is referred to as Avogadro s number S 1 mole of an element has 6.02 x particles

3 Avogadro s Number S To help you better visualize the enormous size of Avogadro's number, 6.02 x 10 23, consider the following analogies: S If we had 1 mole of rice grains, all the land area of the earth would be covered with rice to a depth of about 75 meters! (246 ft) S One mole of rice grains is more grains than the number of all grains grown since the beginning of time. S One mole of marshmallows (standard 1 in 3 size) would cover the United States to a depth of 650 miles.

4 Avagadro s Number S If the Mount St. Helens eruption had released a mole of particles the size of sand grains, the entire state of Washington would have been buried to a depth equal to the height of a 10-story building. S A mole of basketballs would just about fit perfectly into a ball bag the size of the earth.

5 The Mole S 1 mole of Aluminum = 6.02 x atoms S 1 mole of Sulfur = 6.02 x atoms S 1 mole of Water (H 2 O) = 6.02 x molecules of H 2 O S 1 mole of NaCl = 6.02 x molecules of NaCl

6 The Mole S We can use Avogadro s number to convert between the number of moles of a substance and the number of particles it contains. S If you have 4.00 moles of Sulfur (S), how many particles of S do you have? S 4.00 moles S x 6.02 x S atoms = 2.41 x S atoms 1 mole S atoms S If you have 3.01 x molecules of CO 2 how many moles of CO 2 do you have? S 3.01 x CO 2 molecules x 1 mole CO 2 = 5.00 moles CO x CO 2 molecules

7 The Mole S In a chemical formula the subscript numbers indicate the number of atoms of each type of element. S Aspirin s chemical formula is C 9 H 8 O 4 S In a molecule of aspirin there would be 9 Carbon atoms, 8 Hydrogen atoms, and 4 Oxygen atoms. S These number also indicate the number of moles of each element. S Using this information, you can calculate the number actual moles of each element.

8 Calculating Actual Moles of an Element in a Compound S For 1.50 moles of aspirin, C 9 H 8 O 4, how many moles of Carbon, Hydrogen & Oxygen are present? S Carbon: 1.50 moles C 9 H 8 O 4 x 9 moles C = 13.5 moles C 1 mole C 9 H 8 O 4 S Hydrogen:1.50 moles C 9 H 8 O 4 x 8 moles H = 12 moles H 1 mole C 9 H 8 O 4 S Oxygen: 1.50 moles C 9 H 8 O 4 x 4 moles O = 6 moles O 1 mole C 9 H 8 O 4 S How many moles of aspirin contain moles of O atoms?

9 Molar Mass S For any element, the quantity called MOLAR MASS is the quantity in grams that equals the atomic mass of that element. S Atomic mass of C = S Atomic mass of Ag = S Atomic mass of S = g C = 1 mole C g Ag = 1 mole C g S = 1 mole S

10 Molar Mass of a Compound S Molar mass of a compound is the sum of the molar mass of each element multiplied by the number of atoms in the compound. S Atomic mass SO 3 = Mass of S + 3 (Mass of O) = g + 3 (16.0 g) = 80.1 g = 1 mole SO 3 S Atomic mass NaCl = Mass of Na + Mass of Cl = g g = g = 1 mole NaCl

11 Calculations Using Molar Mass S You can use the molar mass to change from moles of a substance to grams or from grams to moles. S If a piece of jewelry requires moles Ag, how many grams of silver are needed? S 1 mole Ag = g of Ag S moles Ag x g Ag = g Ag 1 mole Ag

12 Calculations Using Molar Mass S A box of salt contains 737 g NaCl. How many moles of NaCl are present in that box? S 1 mole NaCl = g NaCl S 737 g NaCl x 1 mole NaCl = 12.6 mole NaCl g NaCl

13 Physical vs. Chemical Changes S What type of change did we see when water boiled? S Physical Change S Altered the appearance but not the formula S If physical change only changes appearance (physical properties), what other changes can happen? S Chemical change S Substances are changed on a molecular level to create new substances S Example: Our reaction to produce elephant toothpaste

14 Chemical Reactions S Chemical reactions produce chemical change. S Bonds between elements are broken and new bonds are formed. S Example: Alka Seltzer in Water: S NaHCO 3 (Sodium Hydrogen Carbonate) and C 6 H 8 O 7 (Citric Acid) react to form CO 2 and other products. S Evidence of chemical reactions: S Change in color S Formation of a gas (bubbles) S Formation of a solid (precipitate) S Heat (or a flame) produced or heat absorbed

15 Chemical Equations S Chemical equations are like a recipe that tells us the materials we need and what will be produced. S If you were going to make a cake: S Flour + Eggs + Sugar + Milk Cake S A simple chemical equation is similar. If you burn charcoal in a BBQ pit: S C (s) + O 2 (g) CO 2 (g) S C & O are called reactants S CO 2 is product S Abbreviations in parenthesis represent the physical state

16 Chemical Equations S Every chemical equation must be BALANCED meaning the number of atoms of reactants must equal the number of atoms of products. S H 2 (g) + O 2 (g) H 2 O (g) S Products: 2 atoms H, 2 atoms O S Reactants: 2 atoms H, 1 atom O S Is this balanced? S Balanced Equation: 2H 2 (g) + O 2 (g) 2H 2 O (g) S Coefficients are placed in front of the formulas S These multiply the formula by the number of the coefficient.

17 Types of Reactions S Most reactions fit into 4 general reaction types: S 1. Combination Reactions- two or more elements combine to form one product. S S (s) + O (g) SO 2 (g) S 2. Decomposition Reactions- a reactant splits into two or more simpler products. S 2HgO (s) 2Hg (l) + O 2 (g)

18 Types of Reactions S 3. Replacement Reactions elements in a compound are replaced by other elements. S Two Types: S Single Replacement a reacting element switches places with an element in the other reacting compound S A + BC AC + B S Zn (s) + 2HCl (aq) ZnCl 2 (aq) + H 2 (g) S Double Replacement the positive ions in the reacting compounds switch places. S AB + CD AD + CB S BaCl 2 (aq) + Na 2 SO 4 (aq) BaSO 4 (s) + 2NaCl (aq)