1. Measurements and Calculations
Units of Measurement

2. Measurements Measurements are quantitative information.
But, they are more than just a number.
MUST have units!!!!

3. SI Measurement Le Système International d’Unités 7 base units
All other units can be derived from those units

4. Mass (m) kilogram (kg)
Length (l) meter (m)
Time (t) second (s)
Temperature (T) Kelvin (K)
Amt of substance (n) mole (mol)
Electric current (I) Ampere (A)
Luminous Intensity (Iv) candela (cd)

5. Mass (m) Measure of amount of matter
NOT equivalent to weight which is a measure of the gravitational pull on matter and is considered a force.
Base unit is the kilogram (kg)

6. Length (l) Base unit is the meter (m) km and cm commonly used
Note that the abbreviation for meter is the same as the symbol for mass.

7. Time (t)
The base unit for time is the second (s)

8. Temperature (T)
The unit used for temperature in science is the Kelvin (K)
Kelvin degrees are the same size as a Celsius degree
But, they are 273 degrees higher
°C = K

9. Amount of Substance (n)
The amount of substance is different from mass
The base unit is the mole (mol)

10. SI Prefixes
The most commonly used SI prefixes in a first year Chemistry course are:
Mega M
Kilo k
Centi c
Milli m
Micro µ
You should be able to convert back and forth between any of these.

11. Derived Units Combinations of base units
Some combinations are given their own names
Joule (measure of energy)
Newton (measure of force)

12. Volume Amount of space occupied by an object Derived unit is m3
cm3 often used and is equivalent to a mL
1 cm3 = 1 mL

13. Density Ratio of mass to volume Derived units are kg/m3
g/mL often used
May be any combination of units that expresses mass/volume

14. Conversion Factors Used to convert from one unit to another
Derived from the equality between two different units
100 cm = 1 m
Can be written as: 100cm/1m or 1m/100cm – both are fractions that are equal to 1

15. Dimensional Analysis
Structured method using conversion factors to solve problems
“Follow the units”
“picket-fence” method

16. Dimensional Analysis
Express 5.712g in kg

17. Dimensional Analysis
Express 25km/h in m/s

18. Dimensional Analysis
How many minutes are there in a week?

19. Dimensional Analysis
What is the density of a 7.45 g sample that occupies 15.6 mL?

20. Dimensional Analysis
What is the mass of a sample of material that has a volume of 64.3 cm3 and a density of 3.67 g/mL?