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Bell Work Prepare for Quiz Write these in your Bell Work Composition Book • Hg • Br • Kr •K •S • Atomic # • Atomic weight • # of protons • # of electrons • # of neutrons • Group • Period Write these in your Bell Work Composition Book • Hg • Br • Kr •K •S Find the Atomic Weight for MgSO4 • Bell work composition book Today’s Element Liquid Metals Zinc Chemical Properties Importance Physical Properties Periodic Table • • • • Atomic # Atomic mass # of Protons # of Electrons • # of Neutrons • Period • Group What’s in a Battery? • • • • • Modern batteries use a variety of chemicals to power their reactions. Common battery chemistries include: Zinc-carbon battery: The zinc-carbon chemistry is common in many inexpensive AAA, AA, C and D dry cell batteries. The anode is zinc, the cathode is manganese dioxide, and the electrolyte is ammonium chloride or zinc chloride. Alkaline battery: This chemistry is also common in AA, C and D dry cell batteries. The cathode is composed of a manganese dioxide mixture, while the anode is a zinc powder. It gets its name from the potassium hydroxide electrolyte, which is an alkaline substance. Lithium-ion battery (rechargeable): Lithium chemistry is often used in highperformance devices, such as cell phones, digital cameras and even electric cars. A variety of substances are used in lithium batteries, but a common combination is a lithium cobalt oxide cathode and a carbon anode. Lead-acid battery (rechargeable): This is the chemistry used in a typical car battery. The electrodes are usually made of lead dioxide and metallic lead, while the electrolyte is a sulfuric acid solution. Water: Separation by Electrolysis Video of Electrolysis: Water to Hydrogen and Oxygen Atomic Mass of a Compound • H2O H2 1.01 x 2 = 2.02 O 16 x 1 = 16.00 1.01 + 1.01 + 16 = 18.02 Try these • CO2 • C6H12O6 Add totals 2.02 + 16.00 18.02 Practice – Finding Atomic Mass • CO2 C 12.01 x 1 = 12.01 O2 16 x 2 = 32.00 Add totals 12.01 + 32.00 44.01 Practice – Finding Atomic Mass • C6H12O6 C6 12.01 x 6 = 72.06 H12 1.01 x 12 = 12.12 O2 16 x 6 = 96.00 Add totals 72.06 12.12 +96.00 108.18 Percent Composition of Mass for Mixtures • A 6g mixture of sulfur and iron is separated using a magnet. Data Sulfur (S) Iron (Fe) 5g 1g • Calculate the percent composition of S and Fe. Percent Composition of Mass for Mixtures • A 6g mixture of sulfur and iron is separated using a magnet. Data Sulfur (S) Iron (Fe) 5g 1g • Calculate the percent composition of S and Fe. Part / Whole x 100 = % composition Sulfur: 5g/6g x 100 = Iron : 1g/6g x 100 = Percent Composition of Mass for Mixtures • A 6g mixture of sulfur and iron is separated using a magnet. Data Sulfur (S) Iron (Fe) 5g 1g • Calculate the percent composition of S and Fe. Part / Whole x 100 = % composition Sulfur: 5g/6g x 100 = 83.33% S Iron : 1g/6g x 100 = 16.66% Fe Use Percent Composition to find the composition of a compound • Use the periodic table to find the compound’s percent composition of each element. • List the atomic weight of each element in the compound • Note how many of each type of atom is in the compound • Add it all up to get the atomic weight of the whole compound Atomic Mass of a Compound • H2O H2 1.01 x 2 = 2.02 O 16 x 1 = 16.00 1.01 + 1.01 + 16 = 18.02 Try these • CO2 • C6H12O6 Add totals 2.02 + 16.00 18.02 Practice – Percent Composition H2O part / whole x 100 = % composition % composition of H % composition of O Practice – Percent Composition CO2 part / whole x 100 = % composition % composition of C % composition of O Practice – Percent Composition C6H12O6 part / whole x 100 = % composition % composition of C % composition of H % composition of O Law of Conservation of Mass • Mass is neither created nor destroyed in any process. It is conserved. Mass reactants = Mass products 2H2O + electricity yields 2H2 + O2 Isotopes • The atomic weight found on the periodic table is based on the average weight of all the isotopes of the element • Isotope – atoms of the same element with the same number of protons but different numbers of neutrons • M&M activity Writing Isotopes Reading Isotopes Mass number - the sum of the protons and neutrons Isotopes of Hydrogen Write Isotopes for Iron More isotopes Argon 36, Argon 37… M&Mium Isotope Activity http://www.chem.memphis.edu/bridson/Fund Chem/T07a1100.htm S.I.Units • http://2012books.lardbucket.org/books/gener al-chemistry-principles-patterns-andapplications-v1.0/section_05.html#averill_1.0ch01_s09_s01_s02_t02 http://chemwiki.ucdavis.edu/Physical_Chemist ry/Atomic_Theory/The_Mole_and_Avogadro's _Constant Measurements and Calculations Where to Round Song Steps in the Scientific Method • 1. Observations • quantitative • qualitative • 2. Formulating hypotheses • possible explanation for the observation • 3. Performing experiments • gathering new information to decide whether the hypothesis is valid Outcomes Over the Long-Term • • Theory (Model) A set of tested hypotheses that give an overall explanation of some natural phenomenon. • • Natural Law The same observation applies to many different systems • - Mass Example - Law of Conservation of Law vs. Theory A law summarizes what happens A theory (model) is an attempt to explain why it happens. Nature of Measurement Measurement - quantitative observation consisting of 2 parts • • Part 1 - number • Part 2 - scale (unit) • Examples: • 20 grams • 6.63 x 10-34 Joule seconds The Fundamental SI Units(le Système International, SI) International System of Units a system of measurement units agreed on by scientists to aid in the comparison of results worldwide. Physical Quantity Mass Name kilogram Abbreviation kg Length meter m Time second s Temperature Kelvin K Electric Current Ampere A mole mol candela cd Amount of Substance Luminous Intensity SI Units Metric Prefixes Common to Chemistry Prefix Unit Abbr. Exponent Kilo k 103 Deci d 10-1 Centi c 10-2 Milli m 10-3 Micro 10-6 Nano n 10-9 Metric Prefixes and Conversion Examples Uncertainty in Measurement • A digit that must be estimated is called uncertain. A measurement always has some degree of uncertainty. Why Is there Uncertainty? Measurements are performed with instruments No instrument can read to an infinite number of decimal places Which of these balances has the greatest uncertainty in measurement? Precision and Accuracy • Accuracy refers to the agreement of a particular value with the true value. • Precision refers to the degree of agreement among several measurements made in the same manner. Neither accurate nor precise Precise but not accurate Precise AND accurate Types of Error • Random Error (Indeterminate Error) measurement has an equal probability of being high or low. • Systematic Error (Determinate Error) Occurs in the same direction each time (high or low), often resulting from poor technique or incorrect calibration. Rules for Counting Significant Figures Details • Nonzero integers always count as significant figures. • 3456 has • 4 sig figs. Rules for Counting Significant Figures Details • • Zeros Leading zeros do not count as significant figures. - • 0.0486 has • 3 sig figs. Rules for Counting Significant Figures Details • • Zeros Captive zeros always count as significant figures. • 16.07 has • 4 sig figs. Rules for Counting Significant Figures Details • • Zeros Trailing zeros are significant only if the number contains a decimal point. • 9.300 has • 4 sig figs. Rules for Counting Significant Figures Details • Exact numbers have an infinite number of significant figures. • 1 inch = 2.54 cm, exactly Sig Fig Practice #1 How many significant figures in each of the following? 1.0070 m 5 sig figs 17.10 kg 4 sig figs 100,890 L 5 sig figs 3.29 x 103 s 3 sig figs 0.0054 cm 2 sig figs 3,200,000 2 sig figs Rules for Significant Figures in Mathematical Operations • Multiplication and Division: # sig figs in the result equals the number in the least precise measurement used in the calculation. • 6.38 x 2.0 = • 12.76 13 (2 sig figs) Sig Fig Practice #2 Calculation Calculator says: Answer 3.24 m x 7.0 m 22.68 m2 100.0 g ÷ 23.7 cm3 4.219409283 g/cm3 4.22 g/cm3 23 m2 0.02 cm x 2.371 cm 0.04742 cm2 0.05 cm2 710 m ÷ 3.0 s 236.6666667 m/s 240 m/s 1818.2 lb x 3.23 ft 5872.786 lb·ft 5870 lb·ft 1.030 g ÷ 2.87 mL 2.9561 g/mL 2.96 g/mL Rules for Significant Figures in Mathematical Operations • Addition and Subtraction: The number of decimal places in the result equals the number of decimal places in the least precise measurement. • 6.8 + 11.934 = • 18.734 18.7 (3 sig figs) Sig Fig Practice #3 Calculation Calculator says: Answer 3.24 m + 7.0 m 10.24 m 10.2 m 100.0 g - 23.73 g 76.27 g 76.3 g 0.02 cm + 2.371 cm 2.391 cm 2.39 cm 713.1 L - 3.872 L 709.228 L 709.2 L 1818.2 lb + 3.37 lb 1821.57 lb 1821.6 lb 2.030 mL - 1.870 mL 0.16 mL 0.160 mL Scientific Notation In science, we deal with some very LARGE numbers: 1 mole = 602000000000000000000000 In science, we deal with some very SMALL numbers: Mass of an electron = 0.000000000000000000000000000000091 kg Imagine the difficulty of calculating the mass of 1 mole of electrons! 0.000000000000000000000000000000091 kg x 602000000000000000000000 ??????????????????????????????????? Scientific Notation: A method of representing very large or very small numbers in the form: M x 10n M is a number between 1 and 10 n is an integer . 2 500 000 000 9 8 7 6 5 4 3 2 1 Step #1: Insert an understood decimal point Step #2: Decide where the decimal must end up so that one number is to its left Step #3: Count how many places you bounce the decimal point Step #4: Re-write in the form M x 10n 2.5 x 9 10 The exponent is the number of places we moved the decimal. 0.0000579 1 2 3 4 5 Step #2: Decide where the decimal must end up so that one number is to its left Step #3: Count how many places you bounce the decimal point Step #4: Re-write in the form M x 10n 5.79 x -5 10 The exponent is negative because the number we started with was less than 1. PERFORMING CALCULATIONS IN SCIENTIFIC NOTATION ADDITION AND SUBTRACTION Review: Scientific notation expresses a number in the form: Mx 1 M 10 n 10 n is an integer 4 x 106 + 3 x 106 7 x 106 IF the exponents are the same, we simply add or subtract the numbers in front and bring the exponent down unchanged. - 4 x 106 3 x 106 1 x 106 The same holds true for subtraction in scientific notation. 106 4x + 3 x 105 If the exponents are NOT the same, we must move a decimal to make them the same. 5 6 40.0 4.00 xx 10 10 + 3.00 x 43.00 = 4.300 x 5 10 x 5 10 6 10 Student A To avoid this NO! problem, move Is this good the decimal on scientific the smaller notation? number! 6 10 4.00 x 6 5 .30xx10 10 + 3.00 4.30 x 6 10 Student B YES! Is this good scientific notation? A Problem for you… -6 10 2.37 x -4 + 3.48 x 10 Solution… -6 -6 -4 002.37 2.37xx10 0.0237 10 x 10 -4 + 3.48 x 10 -4 3.5037 x 10 Direct Proportions The quotient of two variables is a constant As the value of one variable increases, the other must also increase As the value of one variable decreases, the other must also decrease The graph of a direct proportion is a straight line Inverse Proportions The product of two variables is a constant As the value of one variable increases, the other must decrease As the value of one variable decreases, the other must increase The graph of an inverse proportion is a hyperbola