1. Section 2.2 – Units of Measurement
Honors Chemistry
Section 2.2 – Units of Measurement

2. Objectives Students will be able to: Use the SI system of measurement
Identify and use the prefixes
Identify and use the base units
Determine and use derived units
Use mass and volume to calculate density
Solve problems using dimensional analysis
Solve dimensional analysis problems with square and cubic units.

3. SI Measurement
Scientists all over the world have agreed on a single measurement system called Le Système International d’Unités, abbreviated SI.
SI has seven base units
All other units are derived from the seven base units

4. The unit is the standard being used to determine the measurement
SI Base Units
Note – the quantity is the parameter being measured.

5. SI Measurement

6. Note this uses the Base Units – we will more commonly use g/cm3
Derived SI Units
The beauty of this system is all other units are “derived” by combining the seven SI Base Units in different ways.
This simplifies the SI System tremendously compared to the British System
Note this uses the Base Units – we will more commonly use g/cm3

7. Volume
Volume is the amount of space occupied by an object. This is an example of a quantity.
The derived SI unit is cubic meters, m3
The cubic centimeter, cm3, is more commonly used
The liter, L, is a non-SI unit
1 L = 1000 cm3
1 mL = 1 cm3

8. Volume
Video

9. Measuring Liquid Volume
Video

10. Density
Density is the ratio of mass to volume, or mass divided by volume.
Density is a character
The derived SI unit is kilograms per cubic meter, kg/m3
g/cm3 or g/mL are also used
Density is a characteristic physical property (intrinsic property) of a substance.

11. Density Triangle
Mass
Density
Volume

12. Density
Density can be used as one property to help identify a substance

13. Conversion Factors
A Conversion factor is a ratio derived from the equality between two different units that can be used to convert from one unit to the other.
example: How quarters and dollars are related

14. Conversion Factors
Video

15. Conversion Factors
Dimensional analysis is a mathematical technique that allows you to use units to solve problems involving measurements.
example: the number of quarters in 12 dollars

17. Conversion Factors

18. Deriving Conversion Factors
You can derive conversion factors if you know the relationship between the unit you have and the unit you want.
example: conversion factors for meters and decimeters

19. Example Conversion (numbers) Example Conversion (powers of 10)
Si Conversions
Prefix
Symbol
Example Conversion (numbers)
Example Conversion (powers of 10)
tera T
1,000,000,000,000 m = 1 Tm
1 x 1012 m = 1 Tm
giga G
1,000,000,000 m = 1 Gm
1 x 109 m = 1 Gm
mega M
1,000,000 m = 1 Mm
1 x 106 m = 1 Mm
kilo k
1,000 m = 1 km
1 x 103 m = 1 km
hecto h
100 m = 1 hm
1 x 102 m = 1 hm
deka da
10 m = 1 dam
1 x 101 m = 1 dam
deci d
1 m = 10 dm
1 x 10-1 m = 1 dm
centi c
1 m = 100 cm
1 x 10-2 m = 1 cm
milli m
1 m = 1000 mm
1 x 10-3 m = 1 mm
micro
1 m = 1,000,000 µm
1 x 10-6 m = 1 µm
nano n
1 m = 1,000,000,000 nm
1 x 10-9 m = 1 nm
pico p
1 m = 1,000,000,000,000 pm
1 x m = 1 pm
femto f
1 m = 1,000,000,000,000,000 fm
1 x m = 1 fm
atto a
1 m = 1,000,000,000,000,000,000 am
1 x m = 1 am

20. Move Decimal to the Right Move Decimal to the Left
Prefix
Tera
Giga
Mega
Kilo
Hecto
Deka
Standard
Deci
Centi
Milli
Micro
Nano
Pico
Places 3 1
Move Decimal to the Right
Move Decimal to the Left

21. Practice
Using conversion factors, express a mass of grams in milligrams and in kilograms.

23. Converting from large to small or vice versa
When you are doing a complex conversion, it is always better to do it in steps that you know.
If you are changing 5.86 Gm to mm, use the following logic:
Gm m (the base unit) mm

24. Practice
How many km are there in 7.88 Tm?

25. Conversions with Squares and Cubes
Use the cube

26. Conversions with Squares and Cubes
Use the same conversion factor. Square of cube the conversion factor as appropriate.

27. Practice
If you have a plot of land that is 57,000 m2, how many km2 does it cover?

28. Practice (cont.)
If you decided to use this plot of land to give each of your friends a 10 dm2 area to garden. How many friends could you invite?