Introduction to Chemistry CHEMISTRY = the study of the composition of matter, its chemical and physical changes, and the changes that accompany these changes.

DEMO The Think Tube Chemistry is all about trying to figure out things you can’t necessarily see.

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.

DEMO On the Level The Unknown Bubble

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

Density = mass/volume Example: M D V 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

Coke vs. Diet Coke Which is less dense? Meaning which will float in water? Coke or Diet Coke?

WHY is Diet Coke less dense? There is less mass in the same volume (355 mL) Coke has 39 grams of sugar in it to sweeten it (355 + 39 = 394 g) Diet Coke only needs 0.1 g of Nutra Sweet to make is just as sweet as Coke (355 + 0.1 = 355.1 g)

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 Data Data 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.