1. Measurements

2. SI Units
Scientific units that standardize measurements in scientific studies.
SI Units:
Mass: kilograms (kg)
Volume: liters (L)
Length: meters (m)
Temperature: Kelvin (K)
Amount of substances: moles (mol)

3. Common Units Units that are more common in experiments. Common units:
Mass: grams (g)
Volume: milliliters (mL)
Length: centimeters (cm)
Temperature: degrees Celsius (°C)
Amount of substance: moles (mol)

4. Taking measurements in lab
Accurate reading are necessary in lab, the closer you can be to the true value the better
How to read equipment?
Graduated cylinder and the meniscus
Balance
Thermometer
Length

5. Metric System Why use it? Universally understood…except 3 countries
Makes conversions more simple
Prefixes allow for simpler conversions

6. Scientific Notation
Sometimes measurements are too large or too small to be useful
Change them into a format that makes the data more organized.

7. Scientific Notation M.mm x 10n
first digit a # 1 -9
only one nonzero to the left of the decimal point
n = an integer
# of places decimal was moved to get the M.mm value
Ex: km = X 104 km
g = X g

8. Scientific Notation cont…
Helpful hints:
If the number is larger than 1 in ordinary notation, the exponent will be positive
If the number is smaller than 1 in ordinary notation, the exponent will be negative

9. Significant Figures Used to help in making measurements more precise
Follows a specific set of rules
ALL MATH IN CHEMISTRY MUST USE SIG FIG RULES!!

10. Significant Figures Non-zero digits are ALWAYS significant
Ex. 1 L, 2.3 mm, 456 K
Sandwiched zeros are ALWAYS significant
Ex. 101 mL, kPa, g

11. Significant Figures
Zeros at the end of a number containing a decimal are significant
Ex g, L, 20.0 mg
Zeros in front of a number are NEVER significant
Ex mL, 0.01 g, 02 atm

12. Adding/Subtracting
When adding or subtracting, you pay attention to sig figs AFTER the decimal
Examples:
7.459 km km – 0.02 km
1701 g - 50 g + 40 g

13. Multiplying/Dividing
When multiplying and dividing, you pay attention to ALL SIG FIGS
If doing both addition/subtraction AND multiplication and division, this rule WINS!!
Examples:
651 cm x 75 cm
14.75 L ÷ 2.5 L

14. Significant Figure Practice
Solve the problems below, and round using significant figures:
47.0 m x 2.2 m
300.3 L ÷ 180. s
3.61 g g g
(0.001 mL mL) x 2.1 mL

15. Common Prefixes Kilo k 103 Hecto h 102 Deka dk 101 Deci d 10-1
Centi c 10-2
Milli m 10-3

16. Unit Conversions 365.8 mm to dm 2.74 g to kg 0.152 hg to cg
Used to change units into more usable form, or to get a common unit between measurements
Examples:
365.8 mm to dm
2.74 g to kg
0.152 hg to cg
kL to L
mL to cL

17. Dimensional Analysis Read the question.
Identify what you want to find.
Identify what you know.
Set up a conversion bridge to solve the problem, using the correct conversion factor.

18. Dimensional Analysis cont.
Example: In your favorite restaurant, a sandwich you like costs $1.25. If you order 2 sandwiches, how many quarters must you pay?

19. Dimensional Analysis (In class practice)
Pistachio nuts cost $6.00 per pound. How many nuts, in grams, can be purchased for $18.00? (1 lb = 454 g)

20. Dimensional Analysis (In class practice)
How far can Joe drive his car on $30.00 if the car goes 17.8 mi/gal and gasoline costs $1.81 per gal?

21. Dimensional Analysis (In class practice)
Professor Xavier needs to buy marshmallows so his Chemistry students can make S'mores. Each student gets one marshmallow. The marshmallows come 50 per bag and one bag costs $ He has four chemistry I classes with an average of 25 students per class. How much money will he need to collect from his students (total amount in dollars)?

22. Dimensional Analysis (In class practice)
The average speed of the orbiting space shuttle is 17,500 miles per hour. What is the speed in kilometers per second? (1 mi = km)