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!!)

On the Level Observation vs. Inference

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

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.

Density = mass/volume Example 1: What is the density of water if a 5 mL sample of water has a mass of 5 g? M D V

Example 2 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

COKE vs. DIET COKE

Calculations Calculate the density of each: A can of Coke has a volume of 355 mL and a mass of 394 g (assuming that the weight of the aluminum can is constant) A can of Diet Coke has a volume of 355 mL and a mass of 355.1 g (assuming that the weight of the aluminum can is constant)

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 = 355.2 g)

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.

The BUBBLE