Chem 107 1 - First month PDF

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CHEM 107 Aug 23, 2019 THE SCIENTIFIC METHOD 1. Observe a natural phenomena 2. Make predictions to test hypothesis 3. Test the hypothesis 4. Analyze the results a. Accept the hypothesis b. Reject the hypothesis c. Modify the hypothesis d. Refine the hypothesis 5. Establish a theory 6. Continue to test to reproduce results or more observations Measurements- essential for characterizing physical and chemical matter Precision- agreement among repeated measurements EX. Darts hit the same place whether or not it hits the bullseye Accuracy- agreement between a measured value and the accepted or true value EX. Darts hit close to the bullseye Aug 26, 2019 All measurements contain uncertainty – a digit that must be estimated is called uncertain This is where significant figures come into place.

SIGNIFICANT FIGURES -Non zero integers are always significant EX. 7256  4 sig figs 8.29 3 sig figs -Exact numbers (whole number) have an infinite # of sig figs EX. 1 L=1000mL 1 in=2.54 cm ZEROS -Leading zeros are not significant are not significant EX. 0.0392 3 sig figs -Trailing zeros are not significant unless they come after a decimal point EX. 8200  2 sig figs 6230.00 6 sig figs -Captive zeros are always significant (between two non-zero/significant numbers) EX. 43.07 4 sig figs 97.059 5 sig figs Scientific notation is the representation of a number in the form A.XX*10n where A is less than 10 but more than one and n is an integer and every digit included in A is significant. PRACTICE: a) 0.04550 g = 4 sig figs b) 100 lb = 1 sig fig c) 101.05 mL = 5 sig figs d) 350.0 g = 4 sig figs Significant Figures in Mathematical Operations Rounding Off

-Drop only the “insignificant” digits -Only apply this rule at the end of calculations Weakest link principle -The number of sig figs in the final result cannot be greater than the “weakest link” used in the calculation -The actual rule depends on the mathematical operation Multiplication/Division: Answer based on least # of sig figs in calculation EX. 6.38 * 2.0 = 12.76 = 13 2 sig figs Addition/Subtraction: number of sig figs in the result depends on the number of decimal places in the least accurate measurement EX. 68 + 1190 = 1258 = 12703 sig figs Least accurate number (3.43 * 10-2) – (9.8 * 10-4) = 0.03332 = 0.0333 3 sig figs Practice: (1.23 g – 0.567 g) = 1.9 g/cm3 0.34442 cm3 TEMPERATURE CONVERSIONS: _ _ K = C + 273.15 -128.7 F  89.22222 C  362.37222 K C = K – 273.15 C = 5/9 (F - 32) F = C(9/5) + 32

Matter: Atoms, Isotopes, Ions, and Molecules Intensive property -A property that is independent of the amount of substance present. A property that does not change based on size EX. color, melting point Extensive property -A property that varies with the quantity of the substance present. EX. volume, mass Physical Property -A property of a substance that can be observed without changing it into another substance EX. Luster, hardness, color, etc. Chemical Property -A property of a substance that can be observed only by reacting to form another substance EX. Flammability

Classes of Matter Pure substance -Same physical and chemical properties throughout

-Cannot be separated into simpler substances by a physical process Mixture -Combination of two or more pure substances -Can be separated by physical processes August 30, 2019 QUIZ Measurements, atoms, end of today’s lessons Bring a pen, scientific calculator, student id Temperature conversions CHEMFLIX: LN (Library North) 1324C 4:25 pm Tuesdays Homogeneous mixtures are components are distributed uniformly throughout the sample and have no visible boundaries or regions Heterogeneous mixtures are components that are not distributed uniformly, and may have distinct regions of different composition Separating Mixtures: -Distillation -You use the boiling point of one of the components to evaporate the second component -Filtration -Use a porous layer to separate the liquid and solid -Chromatography -Polar solvent will go through faster than the less polar solvent MATTER BREAKDOWN

BRIEF HISTORY OF THE ATOM

The Nuclear Atom -The nucleus -Is the positively charged center of an atom, containing nearly all of the atom’s mass -Is about 1/10000 the size of the atom -Consists of nucleons (particles in nucleus) -Protons are positively charge subatomic particles -Neutrons are electrically neutral subatomic particles The number of protons in an atom is the atomic number, Z. An element will have the same atomic number every time. Atomic mass units (amu) -Unit used to express the relative masses of atoms and subatomic particles -Equal to 1/12 of a carbon atom -6 protons + 6neutrons = 12 amu -1 amu = 1 Dalton (Da)

Broad Categories of Elements -Metals -Shiny solids; conduct heat and electricity; are malleable and ductile -Nonmetals -Solids, liquids and gases; nonconductors; solids are brittle -Metalloids -Shiny solids (like metals); brittle (like nonmentals); semiconductors Atomic Theory -Atomic Symbol -An atomic symbol is a one- or two-letter notation used to represent an atom corresponding to a particular element -The first letter must be UPPERCASE - The second letter, if there is one, must be lowercase - Symbols come from the element name; several names come from Latin Nuclide Symbol -Atomic mass (A) -total number of nucleons (protons+neutrons) in the nucleus -Atomic Symbol (X) -a one or two letter symbol to identify the type of atom -Atomic Number (Z)

-the number of protons in the nucleus; determines the identity of the element Isotopes -Positive ray analyzer results -In 1919, Aston developed a mass spectrometer, and through experimentation, he found two different masses of neon gas atoms exist -90% = 20 amu -10% = 22 amu Isotopes are atoms of an element containing the same number of protons but different numbers of neutrons. Average Atomic Masses -Average atomic mass -weighted average of masses of all isotopes of an element -calculated by multiplying the natural abundance of each isotope by its mass in amu and then summing these products -Natural abundance -proportion of a particular isotope -usually expressed as a percentage relative to all the isotopes for that element in a natural sample AVERAGE ATOMIC MASS EQUATION Ions -Atom has gained or lost electrons -Ions are held together by electrostatic forces Cations are ions with positive charge. Anions are ions with negative charge Ionic Compounds -Made of a metal and a nonmetal -Metals form cations -Nonmetals form anions -Charges on ions depend on location in the periodic table Formula Unit: Smallest electrically neutral unit of an ionic compound

Molecular Compounds -Composed of atoms held together in molecules by covalent bonds and are composed of nonmetals Covalent Bonds -Bond between two atoms created by sharing on or more pairs of electrons Polymer -A very large molecule that is made up of a number of smaller molecules (monomers) repeatedly linked together Molecular formula shows the number and type of atoms in one molecule of a compound Empirical formula shows the smallest whole-number ratio of elements in a compound

Naming Compounds Binary Molecular Compounds -Compounds consisting of two nonmetals First element in the formula is named first – S = sulfur Second element name is changed by adding suffix -ide – O = oxygen → oxide Add prefixes to identify quantity of atoms – SO3 = sulfur trioxide Rules For Using Prefixes 1. Do not use the prefix mono- when naming first element: SO3 monosulfur trioxide  sulfur trioxide 2. Prefixes ending with o- or a- are modified when used with elements beginning with vowels: P4O10 tetraphosphorus decaoxide tetraphosphorus decoxide Naming Organic Compounds and Groups

Binary Ionic Compounds -Binary ionic compounds consist of cations (usually metals) and anions (usually nonmetals), e.g., MgCl2 -Cation named first using name of element Mg = magnesium -Anion named by adding the -ide suffix to the name of the element Cl = chlorine → chloride -Formulas for ionic compounds must always be neutral: Mg2+ + (Cl–) x 2 = 0 - For metals that form cations with different charges, a Roman numeral is added to indicate the charge of the cation

Names of Common Polyatomic Ions Nick the Camel ate a Clam for Supper in Phoenix 1. first letter(s) for element 2. # of consonants = number of oxygens 3. # of vowels = charge Naming Binary Acids -Binary acids -Contain hydrogen and a monoatomic anion (e.g., Cl–, S2–) -Most common binary acids contain halogens (e.g., HCl, HBr) -Acid names: -The prefix “hydro-” + the halogen base name + the suffix “-ic” + the word acid Example: HBr is hydrobromic acid Oxoanions & Related Acids

The Mole: Chemical Formulas, Stoichiometry, Limiting Reactant, Percent Yield The Mole -a unit for a specific number: -1 mole = 6.022 x 1023 particles (also known as Avogadro’s number, NA) Relates mass of a substance to number of particles it contains - convenient unit for expressing macroscopic quantities (atoms or molecules) involved in chemical reactions Mass -Atomic/Molecular mass: -The mass (in amu) of one atom or molecule (1 amu = 1.661 x 10-27 kg) -Molar mass (ℳ): -The mass (in grams) of one mole of the substance (atom, molecule or formula unit) -The mass (in grams) equal to the mass of an individual atom or molecule (in amu) -Formula mass: -Mass in atomic mass units of one formula unit of an ionic compound (e.g., NaCl = 58.43 amu)

Molecular Mass VS Molar Mass

Mole as a Conversion Factor

Conversions

September 9, 2019 Law of Conservation of Mass The sum of the masses of the reactants in a chemical equation is equal to the sum of the masses of the products. EX. Zn + S  ZnS -Mass of reactants (Zn, S) = Mass of products (ZnS) -Coefficients are needed to balance atoms, mass Chemical Equations Describe ratios of reactants (the substances that are consumed) and products (the substances that are formed) during a chemical reaction Coefficients -Indicates ratio of reactants and products on molecular or molar level EX. Fe2O3(s) + 3H2SO4(aq) → 3H2O(ℓ) + Fe2(SO4)3(aq) Balancing Chemical Equations -Law of Conservation of Mass -Total mass of each element on the reactant side and those on product side must be equal -Total charge of reactant side and product side must be equal -Three-Step approach: 1. Write correct formulas for reactants and products, including physical states (if provided) 2. Balance an element that appears in only one reactant and product first 3. Choose coefficients to balance other elements as needed Stoichiometry Quantitative relation between reactants and products in a chemical equation (indicated in chemical equation by coefficients)

Percent Composition The percent composition of a compound is the mass percentage of each element in the compound. -Percentage of each element in a compound can be determined from

HOW TO DETERMINE THE PERCENT COMPOSITION

Finding an Empirical Formula 1. Convert the percentages to grams a) assume you start with 100 g of the compound b) skip if already grams 2. Convert grams to moles a) use molar mass of each element 3. Divide all by smallest number of moles a) if result is within 0.1 of whole number, round to whole number 4. Multiply all mole ratios by number to make all whole numbers a) if already whole numbers, then all set b) if ratio .5, multiply all by 2; c) if ratio .33 or .67, multiply all by 3; d) if ratio .25 or .75, multiply all by 4; etc. Molecular Mass and Mass Spectrometry Mass spectrometers are instruments to determine the mass of substances -Convert molecules into ions -Separate ions based on mass/charge ratio Mass Spectra

Determining the Molecular Formula -Molecular formula determined from: -Mass % composition (empirical formula) -Mass spectral data (molecular mass)

To determine the molecular formula 1. Compute the empirical formula weight 2. Find the ratio of the molecular weight to the empirical formula weight 3. Multiply each subscript of the empirical formula by n Empirical VS Molecular Formulas -Molecular Formula -Actual molar ratio of elements in a compound, equal to some multiple of empirical formula (need empirical formula and molar mass) Combustion Reactions -Reactions between oxygen (O2) and another element in a compound 2 H2 (g) + O2 (g)  2 H2O (g) Hydrocarbons: Molecular compounds composed of only hydrogen and carbon Combustion reactions with C, H, or C, H, O are H2O and CO2 Combustion Analysis - The % of C and H in CaHb determined from the mass of H2O and CO2 produced by combustion CaHb + excess O2  aCO2 +

b 2

H2O (g)

Limiting Reactants -Substance that is completely consumed in the chemical reaction -Determines the amount of product that can be formed during the reaction -Identified by: -# of moles of reactants -Stoichiometry of balanced chemical equation

Percent Yield -Theoretical Yield -The calculated amount of product formed based on the amount of limiting reactant. -Actual Yield -The measured amount of product formed...