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Introduction to Chemistry. CHEMISTRY = the study of the composition of matter, its chemical and physical changes, and the changes that accompany these changes. The Nature of Science. Scientific law versus theory: Scientific law: a summary of an observed natural event.
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Introduction to Chemistry CHEMISTRY = the study of the composition of matter, its chemical and physical changes, and the changes that accompany these changes.
The Nature of Science • Scientific law versus theory: • Scientific law: a summary of an observed natural event. • Scientific theory: a well tested, possible explanation of a natural event.
The Way Science Works… • Science involves critical thinking, or applying logic and reason to observations and conclusions. • Observation vs. Inference • Observation: descriptive of what you see, hear, taste, feel, smell • Inference: an assumption made as a result of an observation (not always correct!!)
Variables and Controls • A variable is anything that can change in an experiment. • Independent variable: The variable being changed or controlled by the scientist. • Dependent variable: The variable being measured or observed by the scientist. • A controlled experiment tests only one variable at a time.
The Scientific Method:A series of logical steps to follow in order to solve problems. • OBSERVE • FORMULATE A QUESTION • FORM A HYPOTHESIS • DESIGN AND CONDUCT AN EXPERIMENT • MAKE OBSERVATIONS • RECORD AND ANALYZE DATA • DRAW CONCLUSIONS • FORMULATE NEW QUESTIONS and CONTINUE CYCLE
Making Measurements • Measurements are made in this class using SI units. • LENGTH (m): distance between 2 points • VOLUME (L): space occupied. • MASS (kg): the amount of matter in an object. • WEIGHT (N): the force with which gravity pulls on a quantity of matter.
Precision vs. Accuracy • Accuracy: the extent to which a measurement approaches the true value. • Precision: the degree of exactness of a measurement. • A scale may be precise to the nearest 100th of a gram, or +/-0.01g
Precision vs. Accuracy increasing precision increasing accuracy
Mind Reading… 75 53 83 Not accurate, not precise 85 85 85 Not accurate, but precise 65 65 65 Accurate and precise! 55 60 80 Accurate, but not precise… Lucky!
Density = mass/volume • Example: • What is the mass of 10 mL of a liquid that has a density of 3.76 g/mL? d = m / v m = dv m = (3.76 g/mL)(10 mL) m = 37.6 g m = 40 g (correct # of sig. figs.) M D V
Temperature Conversions • Temperature is a measure of the average kinetic energy in a system. • K = Kelvin • oF = degree Fahrenheit • oC = degree Celsius • R=Rankin (we won’t use this one in this class)
Temperature Conversions • K = oC + 273 • oF = (1.8 x oC) + 32 • oC = (oF – 32) / 1.8
Percentage Error • Calculate this value in labs where the accepted value is given.
Organizing DataData is organized and presented in tables, charts, and graphs. GRAPHING... Graph - visual representation of data 1) title 2) x and y axis labeled 3) units for both the x and y axis 4) scale is evenly and correctly spaced for data 5) legend when appropriate
LINE GRAPH LINE GRAPH: best for displaying data that change. • Independent Variable: x-axis • Dependent variable: y-axis
BAR GRAPHS BAR GRAPH: useful when you want to compare data for several individual items
PIE CHARTS PIE CHART: ideal for displaying data that are parts of a whole.
