#### Transcript Introduction to Chemistry and Measurement

Welcome to the World of Chemistry Mrs. Panzarella Rm. 351 “The Central Science” Astronomy Nuclear Chemistry Health and Medicine Biology Physics Chemistry Biology Geology Plant Sciences Biochemistry Environmental Science The Language of Chemistry • The elements, their names, and symbols are given on the PERIODIC TABLE (along with reference Table S) http://www.youtube.com/watch?v=6b2Uy1TDAl4 Dmitri Mendeleev (1834 - 1907) Chemical Symbols • Each element on the periodic table is represented by a chemical symbol Chemical Symbols (continued) NOTICE!! The Chemical symbols with two letters are written with a capital first letter and lowercase second letter ELEMENTS TO KNOW Atomic numbers: 1-38, 47, 50-56, 74, 78-80, 82-84, 86, 92, 94 Mass Number Atomic Number • • • • A X Element Symbol Z LEARN the name and chemical symbol spelling counts-use Table S or Agenda (pg R-7) Complete pages 2-3 in Learning Guide Quiz Thursday Chemistry • The study of matter, energy and their interactions Measurement 1) N3: No Naked Numbers. All measurements and answers to math problems must have units written after the numbers. 2) No Work, No Credit. You must show the math set-up when doing math problems. Measurement • Qualitative observation – Focus on the qualities of an object. – Ex. Color of an object • Quantitative observation – Characteristics of an object that can be measured. – Ex. Mass, Length Accuracy vs. Precision • Accuracy - how close a measurement is to the accepted value • Precision - how close a series of measurements are to each other ACCURATE = CORRECT PRECISE = CONSISTENT Can you hit the bull's-eye? Three targets with three arrows each to shoot. How do they compare? Both accurate and precise Precise but not accurate Neither accurate nor precise Precision and accuracy in the laboratory. Figure 1.16 precise and accurate precise but not accurate Significant Figures Indicate precision of a measurement. Includes all digits that can be known precisely plus a last digit that must be estimated 2.35 cm Rules for Significant Figures a. All non-zero digits are significant b. Zeroes between non-zero digits are significant c. In measurements containing an expressed decimal, zeros to the right of NON-ZERO digits are significant. http://www.youtube.com/watch?v=ZuVPkBb-z2I Atlantic/Pacific Rule Pacific = Decimal Present Atlantic = Decimal Absent Count from the ocean towards the coast starting with the first nonzero digit, and include all the digits that follow Significant Figures Counting Sig Fig Examples 1. 23.50 4 sig figs 2. 402 3 sig figs 3. 5,280 3 sig figs 4. 0.080 2 sig figs Significant Numbers in Calculations An answer cannot be more precise than the least precise measurement Adding and Subtracting The answer has the same number of decimal places as the measurement with the fewest decimal places. 25.2 one decimal place + 1.34 two decimal places 26.54 answer 26.5 one decimal place Learning Check In each calculation, round the answer to the correct number of significant figures. A. 235.05 + 19.6 + 2.1 = 1) 256.75 2) 256.8 3) 257 B. 58.925 - 18.2 = 1) 40.725 2) 40.73 3) 40.7 Multiplying and Dividing • Round to the calculated answer until you have the same number of significant figures as the least precise measurement. (13.91g/cm3)(23.3cm3) = 324.103g 4 SF 3 SF 3 SF 324 g Percent Error • Indicates accuracy of a measurement • Formula on Reference Table T experim ent al literature % error 100 literature your value accepted value Percent Error • A student determines the density of a substance to be 1.40 g/mL. Find the % error if the accepted value of the density is 1.36 g/mL. % error 1.40 g/m L 1.36 g/m L 1.36 g/m L % error = 2.9 % 100 DENSITY Mercury 13.6 g/cm3 • an important and useful physical property • standard values can be found on Table S • Density usually decreases as temperature increases because volume increases making the mass more spread out, but the total mass stays the same. One exception!! WATER • Density decreases as the temperature decreases in water Density mass (g) volume (cm3) Density example • An object has a volume of 825 cm3 and a density of 13.6 g/cm3. Find its mass. GIVEN: WORK: V = 825 cm3 D = 13.6 g/cm3 M=? M = DV M D V M = (13.6 g/cm3)(825cm3) M = 11,200 g Metric System • 1. length – The meter is the basic unit of length. The meter stick is divided into 100 equal parts each 1 cm in length » 1km = 103 micro meter – 10-6 m • 2. Mass – The kilogram is the basic unit of mass – 1kg is equal to the mass of 1L of water at 4 C therefore 1g of water equal to the volume of 1cm3(ml) at 4 C • 3. Volume – The space occupied by matter. Derived from measurement of length. – 1L = 1000cm3 1ml = 1cm3 Table 1.3 Common Decimal Prefixes Used with SI Units • Based on powers of 10 Prefix Prefix Symbol Word tera giga mega kilo hecto deka ----deci centi milli micro nano pico femto T G M k h da ---d c m n p f trillion billion million thousand hundred ten one tenth hundredth thousandth millionth billionth trillionth quadrillionth Conventional Notation 1,000,000,000,000 1,000,000,000 1,000,000 1,000 100 10 1 0.1 0.01 0.001 0.000001 0.000000001 0.000000000001 0.000000000000001 Exponential Notation 1x1012 1x109 1x106 1x103 1x102 1x101 1x100 1x10-1 1x10-2 1x10-3 1x10-6 1x10-9 1x10-12 1x10-15 The “Unit fraction” Method aka Dimensional Analysis Steps: 1. Identify starting & ending units. 2. Line up conversion factors so units cancel. 3. Multiply all top numbers & divide by each bottom number. 4. Check units & answer. g cm 3 cm 3 g set up: known value with unit x unknown unit known unit Ex. 1 A rattlesnake is 2.44 m long. How long is the snake in cm? 2.44 m x ______cm m = cm Solution : A rattlesnake is 2.44 m long. How long is the snake in cm? 2.44 m x 100 cm 1m = 244 cm Write and solve for the following problems using the factor label method: 1) 20 cm to m 2) 500 ml to L 3) 0.032 L to mL 4) 45 m to km 5) 805 dm to km 6) 81 cm to mm 7) 5.29 cs to s 8) 3.78 kg to g Scientific Notation • Scientific notation is a way of expressing really big numbers or really small numbers. 65,000 kg 6.5 × 104 kg Move decimal until there’s 1 digit to its left. Places moved = exponent. Large # (>1) positive exponent Small # (<1) negative exponent Graphs should contain the following features: • • • • Independent variable in the X axis (with units) Dependent variable on the Y axis (with units). uniform numerical scale Include a title: (Dependent Variable) vs. (Independent Variable) • Data points, circled with “point protectors”. • Data points connected with a line or a best fit line Done on graph paper in pencil or on the computer