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

In multiplication or division, the solution carries the same number of significant figures as the factor with the fewest significant figures

5.02 x 89.665 x 0.10 = 45.0118 = 45(3 sig figs) (5 sig figs) (2 sig figs) (2 sig figs)

The intermediate result (in blue) is rounded to two sig figs to reflect the least precisely known number (0.10), which has two sig figs.

Significant Figures in Multiplication and Division

In addition or subtraction, the result carries the same number of decimal places as the quantity carrying the fewest decimal places.

It is sometimes helpful to draw a vertical line directly to the right of the number with the fewest decimal places. The line shows the number of decimal places that should be in the answer.

Significant Figures in Addition and Subtraction

In calculations involving both multiplication/division and addition/subtraction, do the steps in parentheses first.

Determine the number of significant figures in the intermediate answer; then do the remaining steps.

3.489 x (5.67 – 2.3) Do not round until the very end

3.489 x 3.37 A line is placed underneath the number to (4 sig figs) (2 sig figs) remind us that we should stop counting sig figs at that point

11.758 will then need to be rounded to two sig figs because of the multiplication rule = 12

Significant Figures Involving Combination of Operations+ - x ÷

6.78 x 5.903 x (5.489 – 5.01)

19.667 – (5.4 x 0.916)

Solve: Significant Figures Combination of Operations

Understanding the Periodic Table

The first letter of all elements in the periodic table is capitalized.

◦ Some elements contain only 1 letter H = hydrogen K = potassium C = carbon O = oxygen

◦ Some elements contain 2 letters, but the second letter is NOT capitalized. Li = lithium Na = sodium Ca = calcium He = helium

Understanding the Periodic Table

C6H12O6

◦ The subscripts “6”, “12”, and “6” tell us how many atoms of each element is in the compound.

◦ This compound contains 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms

6CO2

◦ The coefficient “6” tells us that there are 6 molecules of the compound CO2.

◦ Multiply the coefficient “6” by the amount of each atom to determine the total atoms. 6 x 1 carbon = 6 carbons 6 x 2 oxygen = 12 oxygen

Ca(OH)2

◦ The subscript “2” belongs to the polyatomic anion “OH.” Therefore, we place the “OH” in parentheses to separate it from “Ca.”

◦ This molecule has 1 Ca atom and 2 OH atoms.

Understanding Chemical Formulas

C6H12O6

◦ Carbon’s weight is “12.01” on the periodic table◦ Hydrogen’s weight is “1.01” on the periodic table◦ Oxygen’s weight is “16.00” on the periodic table

To find the molecular mass of the molecule above, multiply the weight of each atom by the number of atoms and add them all up.◦ 6 Carbon x 12 grams = 72 grams of Carbon◦ 12 Hydrogen x 1.01 grams = 12.12 grams of Hydrogen◦ 6 Oxygen x 16.00 grams = 96 grams of Oxygen

72g C + 12.12g H + 96 g O = 180.1 g/mol of C6H12O6

Finding the Molecular Mass

CO2

Ca(OH)2

NaCl H2O H2SO4

H2O2

Na2CO3

CH4

C2H5OH CsOH

Find the Molecular Mass