Intro To Chemistry

Intro To Chemistry

Element Quiz • You will be required to memorize the following elements for the Quiz on Monday • Spelling Counts!! • 1-36, 47, 50, 53, 54, 56-57, 74 • 78-80, 82, 86,92, 94

Elements • 92 Uranium U • 94 Plutonium Pu

CHEMISTRY Is the study of the composition of matter and the changes that matter undergoes, and the energy associated with these changes.

Hypothesis: Tentative proposal that explains observations. revised if experiments do not support it Procedure to test hypothesis; measures one variable at a time. Experiment: Set of conceptual assumptions that explains data from accumulated experiments; predicts related phenomena. Theory(Model): altered if predictions do not support it Further Experiment: Tests predictions based on model. Scientific Approach: Developing a Model Observations : Natural phenomena and measured events; universally consistent ones can be stated as a natural law.

Alchemist at Work(1800’s) • Early chemists • Dealt with religion, medicine, magic and science • Kept inaccurate records due to fear • Four elements • Earth • Air • Fire • Water

Measurement • Quantitive • Give results in a definite form • Usually involving numbers • 20 grams, 273 K • Qualitative • give results in a descriptive non-numeric form

SI Base Units Table 1. 2 time second s temperature kelvin K electric current ampere A amount of substance mole mol luminous intensity candela cd Physical Quantity (Dimension) Unit Abbreviation Unit Name mass kilogram kg length meter m

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 Can you define accuracy and precision?

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

Accuracy & Precision • Accuracy • How close a measurement is to the actual dimension or true value of what is measured • Precision • Reproducibility of the measurement

precise and accurate precise but not accurate Figure 1.16 Precision and accuracy in the laboratory.

Scientific Notation • In exponential form, the number is written as the product of 2 numbers the coefficient and a power of 10 1. The coefficient should always be a number greater than or equal to one and less than 10 2. The subscript indicates how many times the number must be multiplied by 10

Examples • 12 000 00 • 1.2 x 107 • 85 130 • 8.513 x 104 • 0.00072 • 7.2 x 10-4

Significant Figures • Includes all digits that can be known precisely plus a last digit that must be estimated

Significant Figures • Indicate precision of a measurement. • Recording Sig Figs • Sig figs in a measurement include the known digits plus a final estimated digit 2.35 cm

Figure 1.14 The number of significant figures in a measurement depends upon the measuring device. 32.33 oC 32.3 oC

Rules for Sig Figs • 1.Every non-zero digit in a recorded measurement is significant 24.7 ml • 2. Zeros between nonzero numbers are significant • 7003 ml • 3. Zeros appearing in front of all nonzero digits are not significant. 0.0071 ml • 4. Zeros at the end of a number and to the right of a decimal are significant 43.00 • 5. Zeros at the end of a measurement (no decimal shown) • Are confusing 300 m 7000m

Atlantic/Pacific Rule • If decimal is Absent begin counting of the Atlantic side starting with the first whole number • If decimal is Present, begin counting on the Pacific side starting with first whole number

(a)2sf (b) 4sf (c) 5sf (d)4sf (e) 5sf (f) 4sf QUIZ Determining the Number of Significant Figures For each of the following quantities, determine the number of significant figures in each quantity. (a) 0.0030 L (b) 0.1044 g (c) 53,069 mL (d) 0.0000 4715 m (e) 57,600. s (f) 0.0000007160 cm3 SOLUTION:

Sig Figs In Calculations • An answer cannot be more precise than the least precise measurement

Addition and Subtraction • The answer of an addition or subtraction can have no more digits to the right of the decimal point than are contained in the measurement with the least number of digits to the right of the decimal point • 12.52m + 349.0m + 8.24m = 369.76m • 369.8 or 3.698 x 102 74.626m – 28.34 = 46.286 46.29 or 4.629 x 101

Significant Figures • Calculating with Sig Figs (con’t) • Add/Subtract - The # with the lowest decimal value determines the place of the last sig fig in the answer. 3.75 mL + 4.1 mL 7.85 mL 3.75 mL + 4.1 mL 7.85 mL  7.9 mL

Practice • 61.2m + 9.35 + 8.6m • 9.44 – 2.11 • 1.36 + 10.17 • 34.61 – 17.3

Answers • 79.2 • 7.33 • 11.53 • 17.3

Multiplication & Division • The answer must contain no more significant figures than the measurement with the least number of SF • a) 7.55m x 0.34 = 2.567m2 • = 2.6m2 • B) 2.10m x 0.70m = 1.47m2 = • 1.5m2 • C) 2.4526 / 8.4 = 0.291 976m = • 0.29m • D) 0.365m /0.0200 = 18.25m = • 18.3m

You try! • 8.3m x 1.22m = • 1.8 x 10-3m x 2.9 x 10-2m • 8432 / 12.5 • 5.3 x 10-2 / 0.255

Answers • 1.0 x 101 m2 • 5.2 x 10-5 m2 • 6.75 x 102 m • 0.21m

Math Rules For Chemistry: 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 all of the following when doing math problems: the equation you are going to use, the equation rearranged algebraically to solve for the variable you are looking for, the rearranged equation with numbers and units substituted in for all of the variables (numerical setup) and the final answer, rounded properly with units after. 3) The number should also be as precise as the measurement!

your value accepted value Percent Error • Indicates accuracy of a measurement

% error = 2.9 % 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.

SI Base Units time second s temperature kelvin K volume Cubic meter cm3 amount of substance mole mol pressure pascal pa Physical Quantity (Dimension) Unit Abbreviation Unit Name mass kilogram kg length meter m J energy joule

mega- kilo- k M 106 103 BASE UNIT deci- --- d 100 10-1 centi- c 10-2 milli- m 10-3 micro-  10-6 nano- n 10-9 pico- p 10-12 SI Units in metric (based on powers of 10) Prefix Symbol Factor

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 m 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

To the left or right? SI Prefix Conversions 1. Find the difference between the exponents of the two prefixes. 2. Move the decimal that many places.

kilo- mega- M k 106 103 deci- BASE UNIT d --- 100 10-1 centi- c 10-2 milli- m 10-3 micro-  10-6 nano- n 10-9 pico- p 10-12 SI Prefix Conversions Prefix Symbol Factor move left move right

1) 20 cm = ______________ m 2) 0.032 L = ______________ mL 3) 45 m = ______________ nm 4) 805 dm = ______________ km SI Prefix Conversions 0.2 32 45,000 0.0805

Table 1.3 Common Decimal Prefixes Used with SI Units

Density • 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

Densities of Some Common Substances* Table 1.5 Hydrogen Gas 0.0000899 Oxygen Gas 0.00133 Grain alcohol Liquid 0. 789 Water Liquid 0.998 Table salt Solid 2.16 Aluminum Solid 2.70 Lead Solid 11.3 Gold Solid 19.3 Substance Physical State Density (g/cm3) *At room temperature(200C) and normal atmospheric pressure(1atm).

Problem • A copper penny has a mass of 3.1 grams and a volume of 0.35cm3 What is the density of copper? • D = m/v D= 3.1 g/0.35cm3 = 8.8571cm3 = 8.9g/cm3 (2sf)

Problem • A plastic ball with a volume of 19.7 cm has a mass of 15.8g. Would this ball sink or float in a container of gasoline? (gasoline's density is 0.69) • D = 15.8 g/19.7cm3 = 0.802 g/cm3

Sample problem Calculating Density from Mass and Length PROBLEM: Lithium (Li) is a soft, gray solid that has the lowest density of any metal. If a slab of Li weighs 1.49 x 103 mg and has sides that measure 20.9 mm by 11.1 mm by 11.9 mm, what is the density of Li in g/cm3 ?

Density Problems • A 1.00 Liter sample of carbon tetrachloride weighs 1.58 Kg. What is the density of this substance in g/cm3? • Find the mass, volume, or density of a substance when two of these values are known. Examples; • Given: mass = 20g; volume = 10ml; find density • Given: density = 2 g/ml; volume = 10ml; find mass • Given: mass = 20g; density = 2g/ml; find volume

Temperature • Temperature is the degree of hotness or coldness of an object. Heat travels from the hot object to cold object. Heat transfer occurs when two objects at different temperatures contact each other. • Heat travels from the object at high temperature to the one at low temp.

212 ˚F 100 ˚C 373 K 100 K 180˚F 100˚C 32 ˚F 0 ˚C 273 K Temperature Scales Fahrenheit Celsius Kelvin Boiling point of water Freezing point of water Notice that 1 kelvin = 1 degree Celsius

Calculations Using Temperature • Generally require temp’s in kelvins • T (K) = t (˚C) + 273 • Body temp = 37 ˚C + 273 = 310 K • Liquid nitrogen = -196 ˚C + 273 = 77 K

Temperature Scales and Interconversions Kelvin ( K ) - The “Absolute temperature scale” begins at absolute zero (considered the lowest possible temperature 0 K) and only has positive values. Celsius ( oC ) - The temperature scale used by science, formally called centigrade, most commonly used scale around the world; water freezes at 0oC, and boils at 100oC. Fahrenheit ( oF ) -Commonly used scale in the U.S. for our weather reports; water freezes at 32oF and boils at 212oF. Kelvin = oC + 273.15 oC = Kelvin - 273.15 oF = (9/5) oC + 32 oC = [oF - 32 ] 5/9

Kelvin Scale • K = C + 273 • C = K – 273 • The bp of air is 87K. What is the bp in C? • Ethylene glycol is a major ingredient in antifreeze. It boils at 199C. What is bp in K? F?

Intro To Chemistry