Introduction to Chemistry & Experimental Error

Mr. Ramos

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

What is 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.

Branches of Chemistry

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.

System of International Units (SI)

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

Experimental Error

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

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

Significant Figures: Rules

5.12500 0.0204 5.20x1013

5.0x10-3

1 ft = 12 inches 300 0.600 0.3056 0.002

How Many Significant Figures: Solve

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

Scientific Notation

89600000 0.0056 90.80 70000 0.6080 5.26 23.5 34.65 x 102

0.065 x 103

Write in Scientific Notation