EIT Review S2007 Dr. J.A. Mack.

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1 EIT Review S2007 Dr. J.A. Mack Part 1 Atom: The smallest divisible unit of an element Compound: A substance made of two or more atoms Ion: A charged atom or molecule Cation: Positive ion Anion: Negative ion NOMENCLATURE Format for naming chemical compounds using prefixes, suffixes, and other modifications of the names of elements which constitute compounds. 1 2 Sometimes things get confusing inert or noble gasses: Elements: H = hydrogen O = oxygen C = carbon Compounds: H 2 = hydrogen O 2 = oxygen H 2 O = water 3 Metals form Cations non-metals form anions Metalloids can do both 4

Ion Charges: Compounds fall into one of two classes: +1 +2 +3-3 -2-1 Inorganic Salts metal cation Molecules non-metal + + Variable non-metal or polyatomic anion non-metal (no cations or anions) The

2 Ion Charges: Compounds fall into one of two classes: Inorganic Salts metal cation Molecules non-metal + + Variable non-metal or polyatomic anion non-metal (no cations or anions) The two use different formalisms for naming 5 6 Binary Compounds: Metal & non-metal Metal of fixed oxidation (charge) state combined with a non-metal. Examples: non-metal takes on ide suffix Cation Anion Formula Name K + Cl KCl Potassium chloride Ca 2+ O 2- CaO Calcium Oxide Na + S 2- Na 2 S Sodium sulfide Al 3+ S 2- Al 2 S 3 Aluminum sulfide Metals of variable charge (transition) with a non-metal Examples: modify transition metal name with roman numeral Cation Anion Formula Name Pb 2+ Cl PbCl 2 lead (II) chloride pronounced: lead - two - chloride Pb 4+ Cl PbCl 4 lead (IV) chloride Fe 3+ O 2 Fe 2 O 3 Iron (III) oxide 7 8

3 Some common polyatomic ions: NH + 4 ammonium H 3 O + hydronium CO 2 3 carbonate HCO 2 3 hydrogen or bicarbonate NO 2 nitrite NO 3 nitrate SO 2 4 sulfate SO 2 3 sulfite PO 3 4 phosphate C 2 H 3 O 2 acetate Ternary Compounds: Those with three different elements Type A: metal of fixed charge with a complex ion Cation Anion Formula Name K + OH KOH Potassium hydroxide Ca 2+ OH Ca(OH) 2 Calcium hydroxide Na + 2 SO 4 Na 2 SO 4 Sodium sulfate Al 3+ 2 SO 4 Al 2 (SO 4 ) 2 Aluminum sulfate 9 10 Metal of variable charge transition) with a complex ion Non-metal with a non-metal Cation Anion Formula Name When non-metals combine, they form molecules. They may do so in multiple forms: Fe 3+ NO Fe(NO 3 ) 3 Iron (III) nitrate 3 Fe 2+ NO 2 Fe(NO 2 ) 2 Iron (II) nitrite CO CO 2 Because of this we need to specify the number of each atom by way of a prefix. 1 = mono 2 = di 3 = tri 4 = tetra 5 = penta 6 = hexa 7 = hepta 11 12

4 Examples: Formula BCl 3 SO 3 NO we don t write: N 2 O 4 Name: boron trichloride sulfur trioxide nitrogen monoxide nitrogen monooxide or mononitrogen monoxide dinitrogen tetraoxide D) Writing formulas for acids and Bases An acid is a substance that produces H + when dissolved in water. Certain gaseous molecules become acids when dissolved in water. A base produces OH when dissolved in water. Bases often are Group I and Group II hydroxide salts Type I Acids: Acids derived from ide anions. The names for these acids follows the formula: hydro + the root of the ide anion + ic acid Anion: Acid: Name: chloride HCl hydrochloric acid H + and S 2- H 2 S it takes 2 H + to cancel one S 2- hydro sulfuric acid fluoride HF hydrofluoric acid 15 16

5 Examples: Anion: Acid: Name: Practice: N 2 SO 4 sodium sulfate (nitrate) NO 3 HNO 3 nitric acid barium carbonate BaCO 3 (sulfate) 2 SO 4 H 2 SO 4 sulfuric acid FeO zinc phosphide Zn 3 P 2 Iron (II) oxide (acetate) CHO HC 2 H 3 O 2 acetic acid vinegar NiBr 2 nickel (II) bromide CO 2 carbon monoxide P 2 O 5 carbon dioxide CO diphosphorous pentaoxide Common Names: H 2 O water ammonia NH 3 CH 4 methane nitrogen trihydride NH 3 (ammonia) NO N 2 O nitric oxide nitrous oxide 19 20

6 Modern Atomic Theory: please go to my chem. 1A web site and download a nomenclature practice worksheet if you need more review. The link to the worksheet is at the top of the page. Atoms are made of protons, neutrons and electrons. The nucleus of the atom carries most of the mass. It consists of the protons and neutrons surrounded by a cloud of electrons. The charge on the electron is 1 The charge on the proton is +1 There is no charge on the neutron The Atomic Number or number of protons in the nucleus defines an element Isotopes, Atomic Numbers, and Mass Numbers Atomic number (Z) = number of protons in the nucleus. Mass number (A) = total number of nucleons in the nucleus (i.e., protons and neutrons). One nucleon has a mass of 1 amu (Atomic Mass Unit) a.k.a Dalton Isotopes have the same Z but different A. The elements are arranged by Z on the periodic table. By convention, for element X, we write A Z X The isotope 75 34Se is used medically for diagnosis of pancreatic disorders. How many protons, neutrons, and electrons does an atom of have? 75 protons + neutrons 34 protons 75 34Se 75 34Se protons = 34 electrons = 34 neutrons = =

7 Avagadro s Number Since one mole of 12 C has a mass of 12g (exactly), 12g of 12 C contains x C-atoms. But carbon exists as 3 isotopes: C-12, C-13 &C-14 The average atomic mass of carbon is u. From this we conclude that g of carbon contains x C-atoms Molar Masses (Molecular Weights) of Compounds: The molar mass of a molecular compound is the sum of the molar masses of its atoms. Example: The molar mass of CO 2 is: 1 x (12.01 g/mol) + 2 x (16.00 g/mol) Is this a valid assumption? Yes, since N A is so large, the statistics hold. = g/mol How many oxygen atoms are there in 25.1g of chromium (III) acetate? step 1: write the correct chemical formula Cr 3+ & C 2 H 3 O 2 Cr(C 2 H 3 O 2 ) 3 Percent Composition: The relative amounts of each atom in a molecule or compound can be represented fraction of the whole. Question: What is the weight % of each element in C 2? step 2: calculate the molar mass g/mol First determine the molar mass of C 2 : step 3: use dimensional analysis to solve the problem 1mol of C2H6 has a mass of g ( ) g/mol 25.1g Cr(C2H3O 2) 1mol Cr(C2H3O 2) g Cr(C H O ) O atoms = mol O 23 O-atoms 6mol O 1mol Cr(C H O ) Next determine the mass of hydrogen in 1 mol of the compound: 1 mol C2H6 6 mol H 1 mol C H g H 1 mol H = g H 27 28

8 Now relate the mass of H in one mol of the compound to the molar mass of the compound g H g C H = 20.11% H 2 6 Since there is only C as the remaining element: % C = 100 % H = % C The compound C 2 is 20.11% H & 79.89% C Determining a Formula from Percent Composition: Given the relative percentages of each element in a compound, 10 % X, 20 % Y, 30 % Z etc one can find the empirical formula of the compound. The empirical formula of a compound or molecule represents the simplest ratio of each element in 1 mol of the compound or molecule Example: A compound is found to be % carbon, % oxygen and % hydrogen. What is the empirical formula for this compound? Solution: determine X, Y & Z in (C X H Y O Z ) 1. Since the percentages for each element sum to 100%, if one equates % to grams (g), the sum of the masses must be 100g. (i.e. one can assume 100g of the compound) g C g O g H 31 Example: A compound is found to be % carbon, % oxygen and % hydrogen. What is the empirical formula for this compound? 2. Convert the grams of each element to moles. (g element X mole X etc ) 64.82g C 21.59g O 1mol C = mol C g C 1mol O =1.349 mol O g O 1mol H 13.59g H =13.48 mol H g H 32

9 3. Divide each of the individual moles by the smallest number of moles to gain the molar ratios for each element in the compound. These are the formula subscripts. (X 2 Y 3 etc ) Rounding to the nearest whole numbers: X = = 4 Y = =10 Z = = 1 Subscript for C X = = Subscript for H Y = = Subscript for O Z = = **If the ratios are fractional (0.5, 1.5 or 0.333) multiply each ratio by a whole number to get even number formula subscripts. Examples: = = = 1 The empirical formula is: C 4 H 10 O The results of this calculation tells us only about the empirical formula of the compound. To determine the molecular formula, we need more information. This will be shown in a later example Chemical Equations: Mass is conserved in a chemical reaction. Total mass of reactants = Total mass of products Chemical equations must therefore be balance for mass The number and type of atoms on either side of the equation must be equal! Balancing Chemical Reactions: Example C 2 + O 2 CO 2 + H 2 O 2 C s & 6 H s 2 O s 1 C & 2 O s 2 H s & 1 O balance last balance H first 2 C 2 + O 2 CO 2 + H 2 O balance C next 2C 2 + O 2 CO 2 + 6H 2 O balance O 7 2C 2 + O 2 4CO 2 + 6H 2 O 4 C s 12 H s 14 O s 4 C s 12 H s 14 O s

10 Reduction and Oxidation Reactions: RedOx +1 Oxidation Numbers Oxidation involves an atom or compound losing electrons Reduction involves an atom or substance gaining electrons +2 Variable Niether process can occur alone that is, there must be an exchange of electrons in the process. The substance that is oxidized is the reducing agent Metals take on their formal charge: Non-metals do the same The substance that is reduced is the oxidizing agent Chemists use oxidation numbers to account for the transfer of electrons in a RedOx reaction Electrochemistry: Oxidation numbers In the compound potassium bromate (KBrO 3 ), the oxidation number of bromine (Br) is? The compound is neutral so the sum of the oxidation numbers should be zero. +1?? 5 3 (-2) = -6 KBrO 3 1+?? + (-6) = 0?? = 5 39 Balancing REDOX reactions: Fe + O 2 Fe 2 O 3 oxidation states: oxidation half reaction: reduction half reaction: { Fe Fe e - } x 4 { O 2 + 4e - 2O 2- } x 3 Balance electrons transferred then sum the half RXN s: 4Fe + 3O e - 2Fe 2 O e - 4Fe + 3O 2 2Fe 2 O 3 40

11 Quantitative calculations: Mass and moles Consider the following reaction: HCl (aq) + Ba(OH) 2 (aq) H 2 O (l) + BaCl 2 (aq) Balacing: 2 HCl (aq) + Ba(OH) 2 (aq) 2H 2 O (l) + BaCl 2 (aq) How many moles of HCl are consumed if 1.50 g of BaCl 2 are produced assuming that Ba(OH) 2 is in excess? 2HCl (aq) + Ba(OH) 2 (aq) 2H 2 O (l) + BaCl 2 (aq) g BaCl 2 mol BaCl 2 mol HCl 1 mol BaCl g BaCl g BaCl 2 2 mol HCl = mol HCl 1 mol BaCl 2 Solution: convert to then convert to g BaCl 2 mol BaCl 2 mol HCl Molar mass BaCl 2 Molar ratio for equation using the Molar mass of BaCl 2 using the Molar ratio for equation Stoichiometry: Conversions between masses & moles in chemical reactions. Limiting Reactant: When one reactant is present in an amount such that it is completely consumed before all other reactants, we say that it limits the reaction. The other reactants are said to be in excess. The Theoretical Yield is determined by the stoichiometry of the limiting reactant. The limiting reactant can only be determined through molar ratios. It cannot be identified by mass. 43

9/19/07. Chemistry 6A Fall 2007 Dr. J. A. Mack. Molar Masses. Avagagro s s Number. Avogadro s Number and the Mole

9/19/07. Chemistry 6A Fall 2007 Dr. J. A. Mack. Molar Masses. Avagagro s s Number. Avogadro s Number and the Mole Chemistry 6A Fall 007 Dr. J. A. Mack Avogadro s Number and the Mole The concept of a mole is defined so that we may equate the amount of matter (mass) to the number of particles (mole). The Standard is