1. Measurements and Calculations
Chapter 2 – Modern Chemistry

2. 2.1 Scientific Method 5 Steps Observing and collecting data
Collecting data, measuring, communicating
Formulating a hypothesis
Organizing data, classifying, inferring, predicting
Testing
Experimenting, collecting new data, communicating
Theorizing
Constructing models, predicting, communicating
Publish Results
Communicating

3. 2.2 Units of Measurement Systems of Measurement
SI System (International System)
Standardized for Science
Metric System
Used in most parts of the world
English System
Used in the United States

4. Measurements Quantity Units This is what is being measured
Examples: length, mass, temperature, ect
Units
Expression of the quantity
Examples: meter, grams, Kelvin, ect

5. SI Measurements Quantity Quantity symbol Unit Unit symbol Length l
meter m
Mass
kilogram kg
Time t
second s
Temperature T
kelvin K
Amount of
Substance n
mole
mol
Electric Current I
ampere A
Luminous Intensity Iv
candela cd

6. SI Prefixes Prefixes are attached to base units
Base units are grams, meters, liters, and seconds
Prefixes are factors of the base unit
Normally a factor of “x 10”
Largest to smallest with symbols
Tera (T), Giga (G), Mega (M), kilo (k), hecto (h), Deka (da), base unit, deci (d), centi (c ), milli (m), micro ( ), nano (n), pico (p)

7. Derived Units Quantity Quantity Symbol Unit Unit Symbol Area A
Square meter m2
Volume V
Cubic meter m3
Density D
Kilograms per
kg/m3
Molar Mass M
Kilograms per mole
kg/mol
Molar Volume Vm
Cubic meters per mole
m3 /mol
Energy E
joule J

8. Conversion Factor Dimensional Analysis Conversion Factor
Mathematical technique that allows you to use units to solve problems involving measurements
Conversion Factor
A fraction that use two different units of the same quantity in equal amounts to convert the units
Example: Units of money are dollars and cents
If 100 cents = 1 dollar, then 600 cents would equal x dollars?
600 cents x (1 dollar/100 cents) = 6 dollars

9. 2.3 Using Scientific measurements
Accuracy and Precision
Accuracy is the closeness of a measurement
Related back to a true or accepted value
Precision is how close a group of measurements are to each other
Relates back to the other measurements

10. Percent Error
Calculation relating the experimental value to the accepted value as a percentage of difference
Can be greater than or less than 100%
Percent error = (experimental value/accepted value) x 100

11. Significant Figures Rules for significant figures
Zeros between nonzero numbers are significant
Zeros appearing in front of nonzero numbers are not significant
Zeros at the end of a number and to the right of decimal point are significant
Zeros at the end of a number and to the left may vary. If exact measurement, then they are significant. If not an exact measurement, then they are not significant
All nonzero numbers are significant

12. Rounding
We will simplify the rounding of digits to the same number of significant figures as the least amount from the problem
Round any number 5 or greater up and any number 4 or less down

13. Scientific notation
Method of writing values that are either really large or really small in order to simplify the value
Coefficient x 10 ^positive or negative whole number
Coefficient must be less than 10 but greater than or equal to 1
Exponent is positive if the number large and gets smaller
Exponent is negative if the number is small and gets larger
Example: x 10-9

14. Scientific Notation Adding and Subtracting Multiplication Division
In order to add or subtract in scientific notation, the exponents must be the same
Multiplication
Multiply the coefficients and add the exponents
Division
Divide the coefficients and subtract the exponents