Lecture 6

Lecture 6 - 4.1 The Mole Concept and Atoms ...

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Unformatted text preview: 4.1 The Mole Concept and Atoms The Mole and Avogadro's Number Calcula9ng Atoms, Moles, and Mass 4.2 The Chemical Formula, Formula Mass, and Molar Mass The Chemical Formula Formula Mass and Molar Mass 4.3 The Chemical Equa9on and the Informa9on It Conveys A Recipe for Chemical Change Features of a Chemical Equa9on The Experimental Basis of a Chemical Equa9on Strategies for Wri9ng Chemical Equa9ons General, Organic and Biochemistry 7th Edition •  Atoms are exceedingly small Atomic mass unit (amu) carbon- 12 ( 12 C ) assigned the mass of exactly 12 amu 6 •  1 amu = 1.66 × 10- 24 g •  Periodic table gives atomic weights in amu 6 C carbon 12.01 Atomic number is 6, atomic mass is 12.01 amu 12 6 Atomic number is 6, mass number is 12, atomic mass is 12 amu C What is the atomic weight of one atom of fluorine? Answer: 19.00 amu What would be the mass of this one atom in grams? 19.00 amu 1.661 × 10 -24g 3.156 × 10 −23 g × = F atom 1 amu F atom The average mass of carbon atom is: 12.01 amu or 1.995x10- 23 g 12.01 amu 1.661 × 10 -24g 1.995 × 10 −23 g × = C atom 1 amu C atom 12 What is the mass (or weight) of 1 atom of ? 6 C 12 In 12 gram of 6 , how many atoms? Answer: 6.022 × 1023 atoms C 1 atom 12 C 12 amu 6 atoms 1 2 12 grams 6 C = 6.022 × 1023 atoms 1 1 atom H 1 amu 1 1 ? atoms 1 H 23 ? = 6.022 × 10 atoms 1 gram 4 1 atom 2 He 4 amu 4 6.022 × 1023 atoms 2 He 1 mole 4 grams 6.022 × 1023 atoms 1 mole 1 mole of atoms 6.022 × 1023 6.022 × 1023 6.022 × 1023 of atoms Avogadro’s number • Avogadro’s number of atoms of an element has a mass numerically iden9cal to its atomic mass, but in the unit of gram. • 1 mole of atoms of an element has a mass numerically iden9cal to its atomic mass, but in the unit of gram. What is the mass of 2 mols of hydrogen atoms? 2x1.008 = 2.016 g What is the mass of 1 mol of hydrogen molecules? 2x1.008 = 2.016 g •  The atomic mass of one atom of an element corresponds to: –  The average mass of a single atom in amu –  The mass of a mole of atoms in grams –  1 atom of F is 19.00 amu 19.00 amu/atom F –  1 mole of F is 19.00 g 19.00 g/mole F 19.00 amu F 1.66 ×10 −24 g F 6.022 ×10 23 atom F × × 1 atom F 1 amu F 1 mol F =19.00 g /mol 1 What is the mass of 1 mol of 1 H atoms? 1.00 amu 1.66 ×10 −24 g 6.022 ×10 23 atom × × 1 atom 1 amu 1 mol = 1.00 g Calcula9ng Atoms, Moles, and Mass •  Moles atoms or molecules •  Moles mass in g or in kg Calculate the number of atoms in 1.00 g of sulfur. 1 mol S 32.06 g 1 mol S 1.00 g = x mol 32.06 g = 1 mol 1.00g / xmol = 32.06g / 1mol ∴ x = 0.0312 mol 0.0312 x 6.022 x10 23 = 1.88x10 22 Calculate the number of atoms in 1.00 kg of sulfur. Calculate the number of moles in 1.00 kg of sulfur. 6.022 × 1023 atoms S Prac9ce Calcula9ons 1.  Calculate the number of atoms in 1.7 moles of boron. 2.  Find the mass in grams of 2.5 mol Na (sodium). 3.  Calculate the number of atoms in 5.0 g aluminum. 4.  Calculate the mass of 5,000,000 atoms of Au (gold) 4.2 The Chemical Formula, Formula Weight, and Molar Mass •  Chemical formula - a combina9on of symbols of the various elements that make up the compound •  Formula unit - the smallest collec9on of atoms that provide two important pieces of informa9on –  The iden9ty of the atoms –  The rela9ve number of each type of atom Consider the following formulas: •  H2 – 2 atoms of hydrogen are chemically bonded forming diatomic hydrogen, subscript 2 •  H2O – 2 atoms of hydrogen and 1 atom of oxygen, lack of subscript means one atom •  NaCl – 1 atom each of sodium and chlorine •  Ca(OH)2 – 1 atom of calcium and 2 atoms each of oxygen and hydrogen, subscript outside parentheses applies to all atoms inside •  (NH4)3SO4 – 2 ammonium ions and 1 sulfate ion –  Ammonium ion contains 1 nitrogen and 4 hydrogen –  Sulfate ion contains 1 sulfur and 4 oxygen –  Compound contains 2 N, 8 H, 1 S, and 4 O •  CuSO4.5H2O –  This is an example of a hydrate - compounds containing one or more water molecules as an integral part of their structure –  5 units of water with 1 CuSO4 Hydrated copper sulfate Anhydrous copper sulfate Formula Weight and Molar Mass •  Formula weight - the sum of the atomic weights of all atoms in the compound as represented by its correct formula –  expressed in amu •  What is the formula weight of H2O? 16.00 amu + 2(1.008 amu) = 18.02 amu •  Molar mass – mass of a mole of compound in grams / mole –  Numerically equal to the formula weight in amu •  What is the molar mass of H2O? 18.02 g/mol H2O Formula Unit •  Formula unit – smallest collec9on of atoms from which the formula of a compound can be established •  When calcula9ng the formula weight (or molar mass) of an ionic compound, the smallest unit of the crystal is used •  Molar mass - The mass in grams of 1 mole of atoms •  What is the molar mass of carbon? 12.01 g/mol C •  This means coun9ng out a mole of Carbon atoms (i.e., 6.022 × 1023) they would have a mass of 12.01 g •  One mole of any element contains the same number of atoms, 6.022 × 1023, Avogadro’s number What is the molar mass of (NH4)3PO4? 3(N amu) + 12(H amu) + P amu + 4(O amu)= 3(14.01) + 12(1.008) + 30.97 + 4(16.00)= 149.10 g/mol What is the formula mass and molar mass of sodium sulfate? Na2SO4 2(Na amu) + S amu + 4(O amu)= 2x(22.99) + 1x(32.06) + 4x(16.00) = 142.04 amu molar mass of sodium sulfate = 142.04 g/mol 4.3 The Chemical Equa9on and the Informa9on It Conveys A Recipe For Chemical Change •  Chemical equa<on - shorthand nota9on of a chemical reac9on –  Describes all of the substances that react and all the products that form, physical states, and experimental condi9ons –  Reactants – (star9ng materials) – the substances that undergo change in the reac9on –  Products – substances produced by the reac9on Features of a Chemical Equa9on 1.  2.  3.  4.  5.  Iden9ty of products and reactants must be specified using chemical symbols Reactants are wrieen to the lef of the reac9on arrow and products are wrieen to the right Physical states of reactants and products may be shown in parentheses Symbol Δ over the reac9on arrow means that energy is necessary for the reac9on to occur Equa9on must be balanced Features of a Chemical Equa9on 2HgO( s ) Δ !→ ! 2Hg( l ) + O 2 (g ) Products and reactants must be specified using chemical symbols Reactants – wrieen on the lef of arrow Products – wrieen on the right Δ – energy is needed Physical states are shown in parentheses The Experimental Basis of a Chemical Equa9on We know that a chemical equa9on represents a chemical change •  One or more substances changed into new substances •  Different chemical and physical proper9es Evidence of a Reac9on Occurring The following can be visual evidence of a reac9on: • Release of a gas –  CO2 is released when acid is placed in a solu9on containing CO32- ions • Forma9on of a solid (precipitate) –  A solu9on containing Ag+ ions mixed with a solu9on containing Cl- ions • Heat is produced or absorbed –  Acid and base are mixed together • Color changes Subtle Indica9ons of a Reac9on •  Heat or light is absorbed or emieed •  Changes in the way the substances behave in an electrical or magne9c field before and afer a reac9on •  Changes in electrical proper9es Strategies for Wri9ng Chemical Reac9ons •  We will learn to iden9fy the following paeerns of chemical reac9ons: –  combina9on –  decomposi9on –  single- replacement –  double- replacement •  Recognizing the paeern will help you write and understand reac9ons Combina9on Reac9ons •  The joining of two or more elements or compounds, producing a product of different composi9on A + B → AB •  Examples: 2Na(s) + Cl2(g) → 2NaCl(s) MgO(s) + CO2(g) → MgCO3(s) Types of Combina9on Reac9ons 1.  2.  3.  4.  Combina9on of a metal and a nonmetal to form a salt Combina9on of hydrogen and chlorine molecules to produce hydrogen chloride Forma9on of water from hydrogen and oxygen molecules Reac9on of magnesium oxide and carbon dioxide to produce magnesium carbonate Decomposi9on Reac9ons •  Produce two or more products from a single reactant •  Reverse of a combina9on reac9on •  Examples: 2HgO(s) → 2Hg(l) + O2(g) AB → A + B CaCO3(s) → CaO(s) + CO2(g) Types of Decomposi9on Reac9ons 1.  Hea9ng calcium carbonate to produce calcium oxide and carbon dioxide 2.  Removal of water from a hydrated material Replacement Reac9ons 1.  Single- replacement •  One atom replaces another in the compound producing a new compound •  Examples: A + BC → B + AC Cu(s)+2AgNO3(aq) → 2Ag(s)+Cu(NO3)2(aq) 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g) 1.  Replacement of copper by zinc in copper sulfate 2.  Replacement of aluminum by sodium in aluminum nitrate 2.  Double- replacement Two compounds undergo a “change of partners” Two compounds react by exchanging atoms to produce two new compounds AB + CD → AD + CB Types of Double- Replacement AB + CD → AD + CB •  Reac9on of an acid with a base to produce water and salt HCl(aq)+NaOH(aq) →NaCl(aq)+H2O(l) •  Forma9on of solid lead chloride from lead nitrate and sodium chloride Pb(NO3)2(aq) + 2NaCl(aq) → PbCl2(s) + 2NaNO3(aq) Classify each of the following reac9ons as decomposi9on (D), combina9on (C), single- replacement (SR), or double- replacement (DR): ...
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This note was uploaded on 03/07/2012 for the course 830 201 taught by Professor Leyton during the Fall '08 term at Rutgers.

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