1. Introduction to Chemistry Lab Safety Matter
Chapters 1-2

2. SAFETY MATTERS!!!

3. What is Chemistry?
Chemistry: study of the composition of matter & the changes that matter undergoes.
Matter: anything that has volume and mass.
What is NOT matter?
Light, Heat, Radio waves, Magnetic fields

4. Scientific Method
Scientific Method – A systematic approach for learning about the world 1) Observe – an event or process. State the problem and gather background info. 2) Form a Hypothesis – suggested explanation for observed events. 3) Perform Experiments - to test the hypothesis.

5. The Experiment Variables: factors that may change.
Independent Variable (Manipulated Variable)
Change only ONE variable!
Ex. Amount of Fertilizer
Dependent Variable (Responding Variable)
What you measure during the experiment.
Ex. How high the plant grows
Controlled Variables: everything else that must be held constant (so they don’t influence the results).
Ex. amount of water, amount of sunlight, type of soil

6. The Experiment (cont’d)
Control Setup – Exactly like the experimental setup except it DOES NOT contain the variable of interest. Used for comparison
Multiple Trials – To ensure accuracy

7. Scientific Method (cont’d)
4) Record & Analyze Data
- Data – Recorded observations &
measurements
- Create a data table and/or graph
- Analyze – make calculations, use statistics
5) Draw Conclusions Create a theory to explain your results

8. Hypotheses, Theories, Laws
Hypothesis: testable prediction to explain observations
If I drop 2 objects with different weights, the heavier object will hit the ground first.
Scientific Law: a fact of nature that is observed so often it becomes truth.
Makes predictions about what will happen.
The sun will rise every morning.
But does not explain why something happens…
Theory: an explanation based on many observations & experiments.
They answer the question “why”.
Why does the sun rise?  (Heliocentric Theory – Copernicus)

9. Scientific Measurements
Base Units:
Mass – kilogram (gram)
Length – meter
Temperature – Kelvin (Celsius)
Time – second
Derived Units: Consist of a combination of base units
Volume – l x w x h  liter
Density – mass/vol  g/mL

10. Density Density = mass Units: g/mL or g/cm3 volume
Why is it important?
It can help to identify an unknown substance
See reference tables.

11. Measurement Prefixes
Prefixes – Allow scientists to easily convert and represent different magnitudes of a number. (Based on “10”.)
kilo, hecto, deka, base, deci, centi, milli
k h D d c m
“King Henry died by drinking chocolate milk.”

12. Conversions to MEMORIZE
100 centi = 1 base
1000 milli = 1 base
1000 base = 1 kilo

13. Measurements All measurements MUST HAVE: A number (magnitude)
A unit (label)
Ex. 25 mg
Note: Read a graduated cylinder from the
BOTTOM of the meniscus!

15. Accuracy vs. Precision
Accuracy: how close a measurement is to the correct (true) value
Precision: how close a series of measurements are to each other (consistent)

16. Percent Error Percent Error – A way of expressing accuracy
= | theoretical – experimental | x 100%
theoretical
* Theoretical Value – correct value based on
reliable references
* Experimental value – value measured in the
lab

17. Percent Error Example
In lab, you measure the mass of your sample to be 6.2 g. Reliable sources indicate that the actual mass of the sample should have been 8.3 g. What was your percent error?
|6.2 – 8.3| x 100 = 25.3% error
8.3

18. Scientific Notation
Scientific Notation – used to express very large or very small numbers.
Format  (# btwn 1 & 9.9) x 10exponent
Example: 2.6 x 1023
A positive exponent represents a number greater than one.
A negative exponent represents a number less than one.

19. Scientific Notation Practice Ans.
Convert each of the following numbers to standard notation.
a x 105 b. 2.8 x 103 c. 6.1 x 10-2 d. 7.8 x 10-4
340,
Convert each of the following numbers to scientific notation.
a b c. 980,000 d
5.6 x x x x 10-6

20. Graphing Most common type of graph in chemistry  line graph
When constructing a graph:
Title it.
Label axes.
* x-axis  indep. var
* y-axis  dep. var
Scale axes evenly and show units.

21. Graphing (cont’d) Interpreting relationships from graphs:
Direct Proportions – both variables increase or both decrease
Indirect Proportions – one variable increases as the other decreases