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Unit I: Matter and Scientific Calculations. Chemistry I Honors/C101. Objectives #1-6: Matter – Properties and Changes. * The material in Objectives # 1-3 should have been mastered in previous coursework. Demonstrations & Laboratory Exercises will be performed to review the material.
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Unit I: Matter and Scientific Calculations • Chemistry I Honors/C101
Objectives #1-6: Matter – Properties and Changes *The material in Objectives # 1-3 should have been mastered in previous coursework. Demonstrations & Laboratory Exercises will be performed to review the material. *You should be able to answer the questions listed in Discussion Worksheets 1 & 2. Ask for additional assistance if needed--these types of questions will appear on the unit test.
Objectives #1-6: Matter – Properties and Changes *Review the list of elements/symbols and polyatomic ion names/formulas *The list of symbols and names of elements should be memorized for the Unit 1 Test. *The list of polyatomic ions should be memorized before we begin Unit 5.
Objectives #1-5: Classification of Matter Matter - has mass and volume Pure Substances - one type of matter, definite composition Mixtures - more than one type of matter, no definite composition Elements - can’t be broken down chemically Compounds - can be chemically broken down Homogeneous Mixtures (solutions) - can be physically separated, uniform Heterogeneous Mixtures - can be physically separated and not uniform
Demonstrations • Make any notes that will be helpful!
Types & Basic Characteristics of Elements Groups: 1-18; Run vertically; similar chemical properties due to electron configurations Periods:1-7; Run horizontally; same number of energy levels to hold electrons of elements Metals: Groups 1-16 (left of the stairstep line) • Luster • Conducts electricity • Malleable • Ductile • High melting point • Generally solids at room temperature
Types & Basic Characteristics of Elements Nonmetals:Groups 13-18 (right of the stairstep line) • Dull • Insulator • Brittle • Low melting point • Exist as solids, liquids & gases at room temperature
Types & Basic Characteristics of Elements Metalloids: Along the stairstep line, except Aluminum (#13) & Polonium (#84) • Have a somewhat metallic luster • Semi-conductor • Less malleable than metals, but not brittle • Intermediate melting points • Solids at room temp
Objectives #7-8:Basic Math Skills • You should be able to solve the text problems listed below; please come in for help immediately if you need assistance;these types of problems will appear on quizzes and the unit test P. 40 # 1-3 P. 59 # 7, 16, 19 P. 42 # 1,2,3,5 P. 60 # 43, 44 P. 57 # 7, 8
Objective #9: Calculation of Density Note that for water, 1 cm3 = 1ml, so these units are used interchangeably in density calculations! Examples: 1. What is the density of a block of marble that occupies 310. cm3 and has a mass of 853 g? 2. Diamond has a density of 3.26 g/cm3. What is the mass of a diamond that has a volume .351 cm3? Refer to Lab 3 : Determining Density for further details on this topic!!
Objectives #10-13Using Scientific Measurements *All measurements contain some error; the quality of measurements can be determined by determining their: • Accuracy-closeness of a measurement to the true value • Precision- consistency of repeated measurements *Accuracy can be measured by calculating the percent error % Error = Observed Value – Actual Value x 100 Actual Value
Percent Error Examples 500 grams vs. 499 grams: 2 grams vs 1 gram: SO…what does this tell us???? 1 gram difference can result in a large percent error. The purpose of Percent Error is to compare the error of measurement to the standard value so that lab procedures & techniques are modifiedas needed.
The goal of the chemist is to obtain % Error as close to zero as possible!! Note that 0% Error is rarely obtained. Percent Error… • A positive value for percent error indicates that the data is HIGHER than the accepted values… • Possible causes: Impure product, Poor lab technique • How to fix:Clean glassware, follow procedure exactly, allow adequate drying time, preview & practice lab skills before using them during procedure • A negative value for percent error indicates that the data obtained is LESS than the accepted values… • Possible causes: Loss of chemical during transfer, Poor lab technique, inaccurate measuring • How to fix: Take time during procedure to execute skills well, take average of multiple measurements
Using Scientific Measurements • Precision can be determined by significant figures • Significant figures are all digits in a measurement known with certainty, plus the last digit that is estimated • In lab calculations, the number of sig figs in the answer must reflect the least precise instrument used
Determining Significant Figures • Determining significant figures involves a set of rules as summarized on p.47 of text • Examples: 100, 100.01, .800, .00180, 1002 • Practice Problems: 3.0 ____ .10004 ____ .0020 ____ 3000 ____ 2.4421 ____ • Refer to Lab 1: Thickness of a Zinc Coating for further • details on this topic!!
Problem Solving in Chemistry—Dimensional Analysis Dimensional Analysis is a problem solving technique that uses conversion factors to change one unit to another. *Key Steps: Analyze (identify known and unknown) Plan Compute Evaluate (units, reasonable, sig. figs.) What is a conversion factor? • An equivalent relationship that is expressed as a fraction. Ex: 1 kg = 1000 g 1 kg or 1000 g 1000 g 1 kg • Conversion factors are used to switch units within • comparable measurements.
Dimensional Analysis Examples: 1. Convert 14 cm to meters. 2. Convert 1.47 X 10 5 mm to kilometers.
3. A buret delivers .15 cm3 of water per second. How much time is required to transfer 18 grams of water? Assume 1 cm3 = 1 gram for water. 4.The density of an object is 7.5 g/ml. Calculate the mass in grams of a 1.2 L sample.
