Exploring Chemistry: Concepts and Methods in Science

Unit 1: Chemistry and Working With Numbers • Chemist • A person who has the knowledge to change one material with certain properties into a new material with new properties. • Science • A collection of facts that are neither good or bad.

Facts = data. • 2 Types of facts • ) numerical - quantitative • ) descriptive - qualitative • Chemistry - • the study and the investigation of the structures and properties of matter. • Matter - • Anything that has mass and takes up space. • Mass - • the amount of space something occupies. • measured by a balance. • constant.

Weight - • the measure of the pull of gravity on an object. • center of gravity = center of the earth, therefore weight may vary. • increase distance from earth, decrease weight and vice versa (indirect relationship). • measure with a scale.

Inertia the resistance to motion. Scientific Method An orderly and systematic way of answering questions about our world. 1) Define the problem (question). 2) Observe to collect data. 3) Develop a hypothesis (an educated guess based on your data).

4) Test the hypothesis through experimentation. 5) Record and analyze data from experiment. 6) Draw conclusions base on your results. Law describes how nature behaves but does NOT explain why nature behaves that way. Theory explains why nature behaves in the way described by a law.

Variable factor being tested. Experimental Control responds in a predictable way.

Mrs. Hertzog’s notes (to self): 1) Lab equipment (go over eq. and handouts) - check into lab and eq. quiz 2) Lab 1st aid (have students read handout) 3) Lab safety (go over handout) 4) Lab technique (pass out handouts and go over) - quiz on safety and technique

Methods of Separation 1) Decant - pour off the less dense material. 2) evaporate - allow liquid to evaporate off. Will occur at any temperature, but the higher the temperature the quicker the rate of evaporation. temperature and rate of evaporation are directly related (as one goes up so does the other and vice versa). top particles evaporate first.

3) Boil - boil off material with lower boiling point. each material has its own boiling point dependent on its chemical make-up. bottom particles exit first. 4) filter - allow the liquid to pass through the filter paper (filterate) and catch the solid in the filter paper (precipitate).

5) Distill - boil off the liquid with the lower boiling point catch its vapors cool it quickly (condense) and retrap the vapors in a separate container good for materials with similar or equal densities.

6) Chromatography - Chromatography is a method of separation components of mixtures. The name of the method derives from the fact that it was first utilized in the separation of colored substances. The process of chromatography works as a result of several properties of the dissolved substance (size, solubility, and polarity of the molecules). When placed in an appropriate solvent, different substances will move at different rates up a surface,

such as filter paper, as the solvent is absorbed. This difference in traveling rates result in a separation of a mixture into its components.

2 Types of data - • ) qualitative - descriptive • ) quantitative - numerical • International System (SI system) - • Modern version of the metric system. • All measurements consist of numbers and units. • Length • English 1 mile = 5280 ft = 1760 yd 1 yd = 3 ft 1 ft = 12 in

Metric (base unit = meter) • 1 km (kilometer) = 1000 m (meter) • 1 m (meter) = 10 dm (decimeter) • 1 m (meter) = 100 cm (centimeter) • 1 m (meter) = 1000 mm (millimeter) • Mass • English • 1 ton = 2000 lb (pound) • 1 lb = 16 oz (ounce)

Metric (base unit = gram) • 1 kg (kilogram) = 1000 g (gram) • 1 g (gram) = 10 dg (decigram) • 1 g (gram) = 100 cg (centigram) • 1 g (gram) = 1000 mg (milligram) • Volume • English • 1 gallon (gal) = 4 quarts (qt) • 1 qt = 2 pints (pt) • 1qt = 32 fluid ounces (fl oz)

Metric (base unit = liter) • 1 kl (kiloliter) = 1000 l (liter) • 1 l (liter) = 10 dl (deciliter) • 1 l (liter) = 100 cl (centiliter) • 1 l (liter) = 1000 ml (milliliter) • 1 ml = 1 cm3 • Volume = (length)(width)(height) • Volume = (cm)(cm)(cm) = cm3 • when you mult. add exponents

Time - • the interval between 2 occurrences. • Temperature - • a measure of the average kinetic energy of the molecules. • Kinetic Energy (K.E.) - • energy of motion. • as temp. increases so does the K.E., therefore, temp. and K.E. are directly related.

Temperature Scales

Absolute zero - • the temperature at which all motion stops. • Temperature Conversion Formulas: • ) F = (1.8 X C) + 32 • ) C = (F - 32)/1.8 • ) K = C + 273 Order of operations: Please ExcuseMy Dear Aunt Sally Parenthesis,Exponents, Multiplication, Division, Addition, Subtraction

Example Problems and Their Work • ) 95 F -----> C C = (F - 32)/1.8 (formula) C = (95 F -32)/1.8 (plug in) C = 35 C (answer with units!!) • ) 120 C -----> K K = C + 273 (formula) K = 120 C + 273 (plug in) K = 393 K (answer with units!!)

) 300 K -----> F K-----> C ----->F (path - when necessary!) K = C + 273 (formula) K - 273 = C + 273 - 273 (rearrange eq.) C = K -273 (eq.) C = 300 K - 273 (plug in) C = 27.0 C (answer with units!!) F = (1.8 X C) +32 (formula) F = (1.8 X 27.0 C) +32 (plug in) F = 80.6 F (answer with units!!)

Temperature Homework Problems • ) 182 C -----> F • ) 24.0 C -----> K • ) 94.1 K -----> F • ) 154 F -----> K • ) 382 K -----> C Answers: 1) 360 F 2) 297 K 3) -179 C, -290 F 4) 67.8 C, 341 K 5) 109 C

Uncertainty in Measurement = Significant Digits • Significant digits = significant figures (sig figs) • all digits that are certain plus the first uncertain digit. • When making measurements we record only sig figs. • Measurements are uncertain for 2 reasons: 1) instruments are never free of flaws. 2) always involve estimation.

Examples of Reading Instruments and Recording Data According to the Correct Number of Sig Figs See examples on overhead demonstrated by Mrs. Hertzog

Rules for Determining the Number of Sig Figs in a Number 1) All non-zero digits are significant. (ex) 2.56 g answer = 3 (ex) 56,899 yr answer = 5 (ex) 43 ml answer = 2

2) All “sandwiched” zeros are significant. (ex) 3009 m answer = 4 (ex) 60,901 gal answer = 5 (ex) 78,009,003 miles answer = 8

3) Zeros alone to the right of a decimal point are significant. • Gas pump analogy! (ex) 3.00 g answer = 3 (ex) 290.00 in answer = 5 (ex) 7.000020 dl answer = 7

4) Zeros to the right of a decimal point and to the left of a non-zero number are not significant (they are only place holders). • Gas pump analogy! (ex) 0.0009 g answer = 1 (ex) 0.1003 sec answer = 4 (ex) 0.00000045 mg answer = 2

5) Zero in large numbers are significant if underlined or followed by a decimal point. (ex) 4,000,000 yr answer = 1 (ex) 4,000,000 yr answer = 3 (ex) 4,000,000 yr answer 7

Rules for Rounding Numbers 1) Less than 5 • keep it! (ex) 36.3 g (round to 2 sig figs) answer = 36 (ex) 0.5892 g (round to 3 sig figs) answer = 0.589 g 2) More than 5 • round up! (ex) 89.9 yr (round to 2 sig figs) answer = 90. yr (ex) 0.76896 (round to 4 sig figs) answer = 0.7690 yr

3) Exact 5 a) odd rule = round up! (ex) 55 in (round to 1 sig figs) answer = 60 in (ex) 0.007835 in (round to 3 sig figs) answer = 0.00784 in b) even rule = keep it! (ex) 75,650 m (round to 3 sig figs) answer = 75,600 m (ex) 0.0685 m (round to 2 sig figs) answer = 0.068 m

Practice Problems - Rounding 1) 3050 ml (round to 2 sig figs) answer = 3000 ml 2) 0.0551 g (round to 1 sig figs) answer = 0.06 g 3) 678 yr (round to 2 sig figs) answer = 680 yr 4) 1222 dl (round to 3 sig figs) answer = 1220 dl 5) 0.075 cm (round to 1 sig figs) answer = 0.08 cm

Rules for Operations with Sig Figs 1) Mult/Div - round off answers so that they contain the same number of sig figs as the number in your problem with the least number of sig figs. • See examples on overhead! 2) Add/Sub - round off answers so that they contain the same number of decimal places as the number in your problem with the least number of decimal places. • See examples on overhead!

Practice Problems 1) (1.459 in) X (2.1 in) = 2) 18.0 ft3/0.06 ft = 3) 6.0 cm + 9.358 cm = 4) 17.0 g -13.0 g = Answers: 1) 3.1 in2 (in 1+1 = in2) 2) 300 ft2 (ft 3-2 = ft) 3) 15.4 cm 4) 4.0 g

Exponential Notation or Scientific Notation • a simple way of expressing very large and very small numbers. • see overhead for examples! 1) Taking numbers from standard notation and converting them into scientific notation. a) find the decimal point. b) move the decimal point so that your # is greater to or equal to 1, but less than 10. c) count how many places you moved the decimal point and use that as your exponent of 10. Then get rid of all not-significant zeros. d) if the number gets larger the exponent gets smaller and vice versa.

2) Converting a Number From Scientific Notation to Standard Notation • See examples on overhead! a) Make exponent zero. b) Move the decimal point accordingly.

Operations Using Scientific Notation 1) Mult. - mult. numbers and add exponents! • see examples on overhead! 2) Div. - div. numbers and subtract bottom exponent from the top exponent! • see examples on overhead! 3) Add/Sub - get the exponents the same and then perform the indicated operation! • see examples on overhead!

Precision vs. Accuracy • Precision - • how close you come to your original value on repeated trials. • Accuracy - • how close you get to the accepted value. • Actual or Accepted Value (A.V.) - • the correct value. • Experimental Value (E.V.) - • the value you obtained through experimentation.

Percent Error - • your error expressed as a percent. % error = (EV -AV)/AV X 100 • see examples on overhead! Practice Problem: 1) AV = 1.00 g/ml EV = 1.25 g/ml % error = ? answer = 25%

Density • Density - • mass per unit volume. D = M/V • density demos (notes for myself) 1) grad cylinders 2) coke and diet coke • The density of a substance changes with changes in temperature. Ice floats in a glass of water because the solid is less dense than the liquid. • see examples on overhead!

Density Jar Assignment Specifications: 1) Clear, plastic container with a lid (tightly sealed!). 2) A minimum of 5 layers. 3) Each layer must be fully labeled in the order which they settled. 4) Your name and period must be clearly marked on the container. 5) No toxic, alcoholic, or other liquids of which I or your parents would not approve. 6) Do not use household cleaners (Chlorox, ammonia, etc.!).

Practice Density Problems 1) Calcium has a density of 1.54 g/ml. What mass would 3.00 ml of calcium have? 2) Cobalt has a density of 8.90 g/ml. What volume would 17.8 g of cobalt have? Answers: 1) 4.62 g 2) 2.00 ml

Factor Label Method = Dimensional Analysis • a method of converting between units. • Conversion factor - • an equation that shows how different units are related. (ex) 12 in = 1 ft (ex) 1 ton = 2000 lb

1)Conversions requiring only one step (English -English) • see examples on overhead! (ex) 60. in -----> ft answer = 5.0 ft (ex) 80.0 oz -----> lb answer = 5.00 lb (ex) 273 pt -----> qt answer = 136.5 = 136 qt

2) Conversions requiring more than one step (English - English) • see examples on overhead! (ex) 21,120 in -----> miles answer = 0.3333 miles (ex) 5.00 gal -----> fl. oz. answer = 640. fl. oz. (ex) 425 oz -----> tons answer = 0.0133 tons

3) Conversions within the metric system (one step) • see examples on the overhead! (ex) 40.0 dm -----> m answer = 4.00 m (ex) 45.0 ml -----> l answer = 0.0450 l

4) Conversions within the metric system requiring more than one step • see examples on overhead! (ex) 345 cg -----> kg answer = 0.00345 kg (ex) 0.0090 mm -----> dm answer = 0.000090 dm

5) Conversions between the systems (English and Metric) • see examples on overhead! (ex) 8.0 lb -----> g answer = 3632 = 3600 g (ex) 82.0 dm -----> in answer = 323 in ex) 880. mm -----> ft answer = 2.89 ft

Graphing • Graphing - helps you see patterns. • Independent variable - • the variable that the scientist changes in the experiment. • plotted on the horizontal (x) axis. • Dependent variable - • the variable that responds to change in the independent variable. • plotted on the vertical (y) axis.

Steps in Graphing • Each graph that you submit must have the following: 1) Each axis must be labeled with the name of the variable and its units. 2) A numbering system must be devised so that the entire graph paper is used. 3) Mark a dot where all data intersects. 4) Connect the data points with the best possible straight line (unless otherwise told). Not all data points will always fall on your line. 5) Give the graph a suitable title.

Exploring Chemistry: Concepts and Methods in Science