Introduction to Chemistry & Experimental Error

Introduction to Chemistry & Experimental Error Mr. Ramos

What is Chemistry? • Chemistry is the study of matter, and matter is the stuff things are made of. • Matter is anything that takes up space and has mass. • All matter is composed of small particles known as atoms. • Chemistry is known as the central science

Branches of Chemistry • Chemistry has been divided into 5 branches • Organic Chemistry is the study of all substances that contain carbon. • Inorganic Chemistry is the study of substances that do not contain carbon. • Analytical Chemistry is concerned with error and precision, separation, identification, and quantification of substances. • Physical Chemistry is concerned with theories & experiments that describe the behavior of chemicals. In other words, it is the physics of chemicals and reactions. • Biochemistry is the study of the chemistry of living organisms.

System of International Units (SI) • SI Units, also known as System of International Units, are used by scientists all over the words to make conversions easier. • In chemistry we use grams for mass instead of kilograms since we deal with very small quantities.

Experimental Error • There is error associated with every measurement. • Accuracy is a measure of how close a measurement comes to the actual or true value. Keep in mind there is no way to measure the “true” value of anything. • Precision is a measure of how close a series of measurements are to one another; you may be precise but not accurate.

Experimental Error • Suppose you want to measure the boiling point of water with a thermometer and the thermometer reads 99.1°C, but you know that water’s boiling point is actually 100°C. • 100°C, is the accepted value. An accepted value is the correct value based on reliable references. This is also known as the theoretical value. • 99.1°C is the experimental value. This is the value measured in the lab. • Error = experimental value – accepted value

Experimental Error

Significant Figures • Suppose you estimate a temperature that lies between 23°C and 24°C to be 24.3°C. This estimated number has 3 digits. • The first two digits (2 & 4) are known with certainty, but the rightmost digit has been estimated and involves some uncertainty. • Significant figures in a measurement include all of the digits that are known, plus a last digit that is estimated.

Significant Figures: Rules • 1. Every nonzero digit is significant • 24.7, 0.743, and 714 each have 3 sig figs • 2. Zeros between nonzero digits are significant • 7003, 40.79, and 1.503 each have 4 sig figs • 3. Leftmost zeros appearing in front of nonzero digits are not significant • 0.0071, 0.42, and 0.000099 all have 2 sig figs

Significant Figures: Rules • 4. Zeros at the end of a number and to the right of a decimal are always significant • 43.00, 1.010, and 9.000 each have 4 sig figs • 5. Zeros at the rightmost end of a measurement that does not bare a decimal point are not significant; however they are ambiguous. • 300, 7000, and 10,000 all have 1 sig fig • If written in scientific notation, more than 1 sig fig may apply. These numbers are ambiguous • 6. Unlimited sig figs exist in two situations: • Counting: 23 people in the class (this is an exact measurement) • Exactly defined quantities: 1hour = 60 minutes

How Many Significant Figures: Solve • 5.12500 • 0.0204 • 5.20x1013 • 5.0x10-3 • 1 ft = 12 inches • 300 • 0.600 • 0.3056 • 0.002

Scientific Notation • Scientific notation is a way of writing numbers that are too big or too small to be conveniently written in decimal form. • Imagine having to write and read a number this this big: 60221.000 • To write a number in scientific notation, place a decimal between the first two digits of that number. The first digit cannot be a zero. Then, place a x 10n. • 60221.000 becomes 6.0221 x 104

Write in Scientific Notation • 89600000 • 0.0056 • 90.80 • 70000 • 0.6080 • 5.26 • 23.5 • 34.65 x 102 • 0.065 x 103

Introduction to Chemistry & Experimental Error