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ACC CHEM 1311 - CHEMICAL FORMULAS & COMPOSITION STOICHIOMETRY

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1CHAPTER 2CHEMICAL FORMULAS & COMPOSITION STOICHIOMETRY2Atoms and MoleculesDalton’s Atomic Theory - 18081. An element is composed of extremely small, indivisible particles called atoms.2. All atoms of a given element have identical properties that differ from those of other elements.3. Atoms cannot be created, destroyed, or transformed into atoms of another element.4. Compounds are formed when atoms of different elements combine with one another in small whole-number ratios.5. The relative numbers and kinds of atoms are constant in a given compound.Which of these postulates are correct today?3Atoms and Molecules| A molecule is the smallest particle of an element that can have a stable independent existence.z Usually have 2 or more atoms bonded together| Examples of moleculesz H2z O2z S8z H2Oz CH4z C2H5OH4Chemical Formulas| Chemical formula shows the chemical composition of the substance.z ratio of the elements present in the molecule or compound| He, Au, Na – monatomic elements| O2, H2, Cl2– diatomic elements| O3, S4, P8- more complex elements| H2O, C12H22O11– compoundsz Substance consists of two or more elements5Chemical FormulasCompound1 Molecule ContainsHCl 1 H atom & 1 Cl atomH2O 2 H atoms & 1 O atomNH3 1 N atom & 3 H atomsC3H8 3 C atoms & 8 H atoms6Ions and Ionic Compounds| Ions are atoms or groups of atoms that possess an electric charge.| Two basic types of ions:z Positive ions or cations • one or more electrons less than neutralz Na+, Ca2+, Al3+z NH4+- polyatomic cation7Ions and Ionic Compounds| Negative ions or anionsz one or more electrons more than neutralz F-, O2-, N3-z SO42-, PO43-- polyatomic anions8Ions and Ionic Compounds| Sodium chloride (formula unit)z table salt is an ionic compoundNaCl formula unit. 9Names and Formulas of Some Ionic Compounds| Table 2-2 (Table 2- 3 older edition) displays the formulas, charges, and names of some common ions.| Some examples are:z Anions Cl-, OH-, SO42-, PO43-z Cations Na+, NH4+, Ca2+, Al3+10Names and Formulas of Some Ionic Compounds| Formulas of ionic compounds are determined by the charges of the ions.z Charge on the cations must equal the charge on the anions.z The compound must be neutral.| NaCl sodium chloride (Na+& Cl-)| KOH potassium hydroxide (K+& OH-)| CaSO4calcium sulfate (Ca2+& SO42-)| Al(OH)3aluminum hydroxide (Al3+& 3 OH-)11Names and Formulas of Some Ionic Compounds| Table 2-1 (Table 2- 2 older edition) gives names of several common molecular compounds.| Some examples are:z H2SO4– sulfuric acidz FeBr2– iron(II) bromidez C2H5OH – ethanol| You will need to know the molecular compounds in this table.12Names and Formulas of Some Ionic Compounds| What is the formula of nitric acid?z HNO3| What is the formula of sulfur trioxide?z SO3| What is the name of FeBr3?z iron(III) bromide13Names and Formulas of Some Ionic Compounds| What is the name of K2SO3?z potassium sulfite | What is charge on sulfite ion?z SO32-is sulfite ion| What is the formula of ammonium sulfide?z (NH4)2S14Names and Formulas of Some Ionic Compounds| What is charge on ammonium ion?z NH4+| What is the formula of aluminum sulfate?z Al2(SO4)3| What is charge on both ions?z Al3+and SO42-15Atomic Weights| Weighted average of the masses of the constituent isotopes if an element.z Tells us the atomic masses of every known element.z Lower number on periodic chart.| How do we know what the values of these numbers are?16The Mole| A number of atoms, ions, or molecules that is large enough to see and handle.| A mole = number of thingsz Just like a dozen = 12 thingsz One mole = 6.022 x 1023things| Avogadro’s number = 6.022 x 1023z Symbol for Avogadro’s number is NA.17The Mole | How do we know when we have a mole?z count it outz weigh it out18The Mole| Molar mass - mass in grams numerically equal to the atomic weight of the element in grams.| H has an atomic weight of 1.00794 g z 1.00794 g of H atoms = 6.022 x 1023H atoms| Mg has an atomic weight of 24.3050 g z 24.3050 g of Mg atoms = 6.022 x 1023Mg atoms19The Mole| Example 2- 1: Calculate the mass of a single Mg atom, in grams, to 3 significant figures.23231 24.301 6.022 10 1 4.04 10 mol Mg atoms g M gMg atomMg atoms mol Mg atomsgMg−=×=×20The Mole| Example 2- 2: Calculate the number of atoms in one-millionth of a gram of Mg to 3 significant figures.236 161 mol Mg 6.022 10 Mg atoms1.00 10 g Mg 2.48 10 Mg atoms24.30g Mg 1 mol Mg atoms−××=×21The Mole| Example 2- 3. How many atoms are contained in 1.67 moles of Mg?23246.022 10 Mg atoms1.67 mol Mg 1.00 10 Mg atoms1molMg×=×22The Mole| Example 2- 4: How many moles of Mg atoms are present in 73.4 g of Mg?1 mol Mg atoms73.4 g Mg 3.02 mol Mg24.30 g Mg=IT IS IMPERATIVE THAT YOU KNOWHOW TO DO THESE PROBLEMS23Formula Weights, Molecular Weights, and Moles| How do we calculate the molar mass of a compound?z add atomic weights of each atom| The molar mass of propane, C3H8, is:amu 44.11 mass Molaramu 8.08 amu 1.01 8H 8amu 36.03amu 12.01 3C 3==×=×=×=×24Formula Weights, Molecular Weights, and Moles| The molar mass of calcium nitrate, Ca(NO3)2, is:amu 164.10 massMolar amu 96.00 amu 16.006 O6amu 28.02 amu 14.012 N2amu 40.08 amu 40.081 Ca1==×=×=×=×=×=×25Formula Weights, Molecular Weights, and Moles| One Mole of Containsz Cl2or 70.90g 6.022 x 1023Cl2molecules2(6.022 x 1023) Cl atomsz C3H8 or 44.11 g 6.022 x 1023C3H8molecules3 (6.022 x 1023) C atoms8 (6.022 x 1023) H atoms26Formula Weights, Molecular Weights, and Moles| Example 2- 5: Calculate the number of C3H8molecules in 74.6 g of propane.2338 383838 38241 mole C H 6.022 10 C H molecules74.6 g C H44.11g C H 44.11 g C H1.02 10 molecules ×=  =×27Formula Weights, Molecular Weights, and Moles| Example 2- 8. Calculate the number of O atoms in 26.5 g of Li2CO3.2323 232323 23 23231 mol Li CO 6.022 10 f.w. Li CO 3 O atoms26.5g Li CO73.8 g Li CO 1 mol Li CO 1 f.w. Li CO= 6.49 10 O atoms ×=  ×28Formula Weights, Molecular Weights, and Moles| Occasionally, we will use millimoles. z Symbol - mmolz 1000 mmol = 1 mol| For example: oxalic acid (COOH)2z 1 mol = 90.04 g z 1 mmol = 0.09004 g or 90.04 mg29Formula Weights, Molecular Weights, and Moles| Example 2- 9: Calculate the number of mmol in 0.234 g of oxalic acid, (COOH)2.22221 mmol (COOH)0.234 g (COOH)


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ACC CHEM 1311 - CHEMICAL FORMULAS & COMPOSITION STOICHIOMETRY

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