1. St. Augustine Preparatory School August 7 Lecture
Chemistry Chapter 2
St. Augustine Preparatory School
August 7 Lecture

2. Observations Observations can be qualitative or quantitative
Qualitative relates to a quality of something such as color, texture, shape
Something you see, feel, hear, etc.
Quantitative relates to quantity – something that is measured. Ie. 10 meters, 29.5°C, 4 students, etc.

3. Hypotheses and Variables
Hypotheses are testable statements made prior to beginning an experiment or lab
During an experiment, we have both controls (stays the same) and variables (what is changed).
The changes or results we observe will likely be a result of the variable(s).

4. Scientific Method
Observations are made or current evidence is evaluated
A hypothesis must be made – what is expected to be found?
Testing – experiment, measure, and collect data
Theorizing – What did your data tell you?
Publish results – this allows others to benefit from your research

5. SI Units In 1960, it was decided to have 7 base units
Meter (length) symbol: m
Kilogram (mass) symbol: kg
Seconds (time) symbol: s
Kelvin (temperature) symbol: K
Mole (amount of substance) symbol: mol
Ampere (electrical current) symbol: A
Candela (how bright something is) symbol: cd

6. Other units There are more than these 7 units in science!
Units that come from a combination of the 7 base units, such as velocity (m/s), area (m2), or volume (m3) are called derived units
There are also non-SI units that are widely accepted and used in science, such as Liters
1 liter = 1000 cm3

7. Conversion of Numbers
When numbers are placed in formulas, they must have the correct units in order to be used!
This means we may have to do some math with our number before we can use it
Example: mass (m) in chemistry requires that the mass be in grams for the formula m=nM.

8. Conversions There are 1000 milliliter in 1.0 liter
There is liter in 1.0 milliliter
There is 1000 mg in 1.0 gram
There is grams in 1.0 milligram
There is 1000 grams or liters in 1 kilogram or kiloliter
There is kL or kg in 1 L or 1 g

9. Conversion of Numbers Example 1: Convert 0.321kg to grams
Example 2: Convert 32.67mL to liters

10. Try these on your own 132.7 milligrams to grams
kilograms to milligrams
235 grams in kilograms
milliliters to liters
0.68 kiloliters in liters
0.003 kiloliters in milliliters

11. Accuracy and Precision
Accuracy: How close to the actual value a measurement is
Precision: How close together two or more measurements are to each other.
You can be precise, without being accurate!

12. Consider the game of darts, if a person is aiming at the center of the board.

13. Percent Error
Percentage Error – used to calculate how close to the actual value your experimental value is.

14. Percent Error Questions
You are given a water sample that contains 2.304mg of Mercury. You run tests on it, and conclude that it was 2.516mg of mercury. What is your percent error?

15. Percent Error Questions
You receive another water sample and are told that it contains g of phosphorous. After testing the sample, you find that it has 3.79mg of phosphorous. What is the percent error?