Chemistry and the Scientific Method

Chemistry and the Scientific Method Chapter 2 (little part of 1) 1. Chemistry – the Central Science • The study of the relationships between the structure and properties of matter and • Chemists use this information to discover new materials and identify • Production of Chemicals • Raw Materials – Chemicals found in • Intermediate Chemicals – Chemicals that are produced and used in another chemical process to produce consumer • Consumer Product – Products sold to consumers or to manufacture • Chemists • Solve problems dealing • Find relationships between structure and properties • Use this knowledge to “discover” • Identify samples of Chemical Engineers • Design, build, operate, and troubleshoot Branches of Chemistry • Organic Chemistry – Matter containing • Inorganic Chemistry – Matter that does not • Physical Chemistry – Properties and transformations of matter and the related • • • • • predict chemical 2. Problem Solving Techniques Biochemistry – Matter and process in Analytical Chemistry – Components, composition, Theoretical Chemistry – Use of mathematics and computers to understand and • List possible • Look for a • Make a • Make a • Trial and • Work • Solve a simpler or similar • Scientific Scientific Method 1. State the problem and make 2. Form a hypothesis that could 3. Test the hypothesis – 4. Collect data Strategies used by scientists and engineers to solve problems. 5. Form a 6. Scientific Law – a rule of nature – used to Page 1 of 10 • • • 7. Scientific Theory – a statement of an idea based on Experiment: • Test a hypothesis – an educated guess, • Has two Dependent Variable – Independent Variable – you manipulate, • Has Constants – items in the experiment that • Has a control experiment – a way to make a comparison, an experiment that reflects the • Have a detailed procedure – a list of steps that everyone can follow so they can repeat the Record data and Analyze the data – make • Independent variable goes on the horizontal (X) axis. Time • Dependent variable goes on the • Repeat the experiment • Observations • Qualitative Data – Description of the physical properties of matter. An observation made without making a measurement. Describes Examples – • Quantitative Data – Measurements made that describe the matter. “Quantity”, Examples – Two parts – How much and 3. Research and Technology • Basic (pure) Research – scientists that work to gain knowledge. They are answering • Examples – • Applied Research – scientists that are working to • Examples – • Technology – practical use of research, • Examples – SI Units and Scientific Notation 1. SI • • • • • • • • System SI system uses Easy to Used worldwide by Prefix Symbol Mega Kilo Hecto Deka Amount Examples Page 2 of 10 • • • • • Deci Centi Milli Micro Nano Base – no prefix 2. SI Units SI Base Units – • Mass – o Standard unit is kilogram (kg), gram is too small to o Defined by a cylinder o Measure using a balance – compare mass • Length – shortest distance o Standard unit o Defined by the distance light travels in a vacuum in 1/299,792,458 o Use a • Time – interval o Standard unit is o Defined by the frequency of radiation emitted from a o Use a stopwatch, clock • Temperature – average kinetic energy of all the particles o Standard unit o Kelvin = o No negative o Kelvin is used when o Absolute Zero = o No motion of atoms, electrons, o Gasses have o Water freezes at o Water boils at o Measure temperature with Derived Units– Combination of • Speed – distance/time, • Area – length x width, • Weight – force of gravity (attraction) o Not a SI Base Unit – It is o Unit is o Measure using a scale (spring) – amount of o Weight depends on • Volume – amount of space o length x o Meter x o Solids – Page 3 of 10 • Liquids – Measure volume of a liquid in Measure volume of a solid by liquid displacement ( o 1 dm3 = 1 Liter = o 1 mL = o Liter is a derived unit because it is Density – mass per unit volume, how closely packed matter is o Density = o o o Density can change with temperatures, especially for gases, most densities are given o Density of water, at 25ºC, o Object’s density < 1.0 g/mL, object o Object’s density > 1.0 g/mL, object o Object’s density = 1.0 g/mL, object is 3. Problem Solving / Word Problems 1. Read the problem all Get a general idea of what the 2. Write down the What do I know? What information 3. Formulas Relationship between the 4. What other information Constants, data from Connversion 5. Solve Plug and chug. Carry your units 6. Are the units for my answer correct? Answers always have Numerical + How much 7. Is the answer reasonable? o You are given an unknown substance. You measure the mass to be 107 g and the volume to be 12 cm3. What is the density? Page 4 of 10 I know the density of aluminum is 2.7 g/cm3. I need 252 cm3 for a project. What mass of aluminum do I need? I know the density of oak wood is about 0.710 g/cm3. I weigh a square block of this wood and determine it has a mass of 765 grams. What is the volume of the block? 4. Factor-Label • If quantities are equal, you can set up a factor and use this to • 1000 mm = 1 m • • • • • • • • • 2 m = ? mm 250 mm = ? m 7.5 mm = ? km 0.750 mL = ? L 35.75 cm = ? mm 237.5 g = ? kg 52,500 dm = ? km 263.2 cm = ? m Page 5 of 10 • • • 7.856 kg = ? g 90 km/hr = ? m/s 1m3 = ? cm3 85 cm = ? nm 584 s = ? s • • 5. Scientific Notation • A way to write very, very large or very, • A number with a digit between 1 and 9, inclusive, • As the decimal moves left, the exponent • As the decimal moves to the right, the exponent • 2,000 m = • 0.002 m = • 0.021 m = • 36001000 m = • 0.040 m = • 0.122 m = • Add/Subtract – Exponents must be the same. o (2.30 x 102m) + (2.30 x 103m) = o (5.1 x 10-2m) + (6.2 x 10-1m) = o (2.5 x 103m) – (1.2 x 102m) = • Multiply – add exponents o (2.0 x 102m) x (2.0 x 103m) = o (2.0 x 10-2m) x (2.0 x 103m) = • Divide – Subtract exponents o (1.0 x 10-2g) ÷ (2.0 x 10-4mL) = o (3.0 x 103g) ÷ (2.0 x 104mL) = Measurements and Graphing 1. Accuracy • How close a measurement is • Depends on the equipment and how well • Standards are published in • Percent Error is a calculation to determine how • 2. Precision • How repeatable your • How well you repeat the measurement and get • Percent Difference is a calculation to determine how precise • Page 6 of 10 You measured the boiling point of water to be 99.6°C. What is the percent error? You measure the density of magnesium to be 1.92 g/cm3. What is the percent error? Standard density of Mg = 1.738 g/cm3 You measure and calculate the density of an unknown to be 3.25 g/mL. The second time you do the experiment, you calculate it to be 3.36 g/mL. What is the percent difference of these two values? 3. Significant Figures • Use to tell how exact your • Last digit you read is an estimate, and it is • Digits other than zero o 123 344 56,789 • One or more final zeros used after the decimal point o 12.0 12.30 12.301000 • • • Zeros between two other significant digits o 102 100.1 100.00 Zeros used solely for spacing the decimal point o 0.01 100 0.0033 0.0303 Counting numbers (conversion factors) have infinite number o 5 days 1000 g = 1 kg 2 students Page 7 of 10 • How many sig figs? o .0013 g o 70.020 g o 100,000 mg o 200,000.0 mm o 1.000300 g o 1,000,300 mg o 937 kg o 0.223 g o 0.002300 mm Rounding to the correct number of sig figs o 2 sig figs : 3.150 → o 2 sig figs : 3.149 → o 2 sig figs : 3.151 → o 2 sig figs : 3.156 → Round o o o o 12.783456 cm to : 2 sig figs : 5 sig figs : 6 sig figs : 7 sig figs : • • Round each to 4 sig figs o 84,791 kg → o 38.5432 g → o 256.75 cm → o 0.00054818 g → o 2.0145 mL → o 89,218 g → o 199,870 mm → o 126,778.43 L → 4. Calculations using Significant Figures • Addition and Subtraction – in addition and subtraction, the answer may contain only as many decimal places as the measurement having the least number of o 966.5 kg + 25.26 kg = Least position at tenth = o 745.88 kg - 101 kg = Least position at ones = o 1.37 g + 1.251 g = Least position at hundredths = o 1287 m – 200 m = Least position at hundreds = • Page 8 of 10 • Multiplication and Division – In multiplication and division, the answer may contain only as many significant digits as the measurement with the least number o 25.301 m x 2.01 m = o (5) (3) → o 125.2 kg ÷ 101.456 m3 = o (4) (6) → 5. Graphs • Pie Graphs – (circle graph) Shows the percent of each component • Bar Graphs – Used to compare how the dependent variable varies • Line Graphs – Used to show a trend. The data points • Scatter Graphs – Show a relationship between the independent and o We draw a “best fit” line. This line can be a curve. It shows how the The collected data DOES NOT have to be on the line. The experimental data should 6. Types Relationships: • Direct Relationship Draw a Graph o Linear – o y= o Y= o X= o m = slope = o b= • Quadratic Relationship Draw a Graph o Exponential – o y= o y= o k= o x= • Inverse Relationship Draw a Graph o Hyperbola o xy = o y= o k= o x= o 7. Making Graphs • Use the • Give the graph a • Label the • Units for • Scale the ranges to Page 9 of 10 Lab Safety 1. No food or drink 2. Burners and Hot Plates • Wear goggles and • Tie long • No loose • No dangling • Do not place chemical bottles, combustibles (paper) near the hot • Point test tubes you are heating away from • Once you have lit the burner, adjust the air until you have a 3. Measuring Mass • Zero the • Do not put any chemical on the pan, always use wax paper or a • Record tare weight and subtract from 4. Measuring temperature • Try to place the thermometer in the center of the liquid, not touching the bottom or sides • NEVER use the thermometer to 5. Measuring Volume • Use a graduated cylinder on • Liquids usually form a meniscus – read the bottom or the top • Read by looking at the meniscus 6. Transferring Chemicals • Use a spoon or spatula • Wear goggles and • NEVER put chemicals, used or unused back into 7. Smelling • If mixing chemicals that form poisonous gases (some colored some not) or vapors – do this under • Use a fanning (wafting) motion to draw vapors 8. Diluting Acids (and bases) • ACID INTO • Acid gives off a large amount of heat when • Pour slowly and use • WEAR GOGGLES, apron, gloves, and perform in 9. Injuries • Report any injuries • Do not put your hands in the sinks, there might be • Safety shower – pull down handle and stay under for • Safety eye wash – hold eye lids open and allow water to flush eyes for • NO HORSEPLAY! Page 10 of 10