1. 2.6 SI Units
The International System of Units, SI, is a revised version of the metric system
Correct units along with numerical values are critical when communicating measurements.
The are seven base SI units (Table 2.1) of which other SI units are derived.
Sometimes non-SI units are preferred for convenience or practical reasons

3. 2.6 SI Units – Table 2.2 Quantity SI Base or Derived Unit Non-SI Unit
Length
meter (m)
Volume
cubic meter (m3)
liter
Mass
kilogram (kg)
Density
grams per cubic centimeter (g/cm3); grams per mililiter (g/mL)
Temperature
kelvin (K)
degree Celcius (°C)
Time
second (s)
Pressure
Pascal (Pa)
atmosphere (atm); milimeter of mercury (mm Hg)
Energy
joule (J)
calorie (cal)

4. Common SI Prefixes Units larger than the base unit Tera T
e12 base units
termeter (Tm)
Giga G
e9 base units
gigameter (Gm)
Mega M
e6 base units
megameter (Mm)
Kilo k
e3 base units
kilometer (km)
Hecto h
e2 base units
hectometer (hm)
Deka da
e1 base units
decameter (dam)
Base Unit
e0 base units
meter (m)

5. Common SI Prefixes Units smaller than the base unit Base Unit
e0 base units
meter (m)
Deci d
e-1 base units
decimeter (dm)
Centi c
e-2 base units
centimeter (cm)
Milli m
e-3 base units
millimeter (mm)
Micro μ
e-6 base units
micrometer (μm)
Nano n
e-9 base units
Nanometer (nm)
Pico p
e-12 base units
picometer (pm)

6. Common SI Prefixes
A mnemonic device can be used to memorize these common prefixes in the correct order:
The Great Monarch King Henry Died By Drinking Chocolate Mocha Milk Not Pilsner

7. 2.7 Units of Length The basic unit of length is the meter
Prefixes can be used with the base unit to more easily represent small or large measurements
Example: A hyphen (12 point font) measures about m or 1 mm.
Example: A marathon race is approximately
42,000 m or 42 km.

8. 2.7 Concept Practice
15. Use the tables in the text to order these lengths from smallest to largest.
a. centimeter
b. micrometer
c. kilometer
d. millimeter
e. meter
f. decimeter
- 3
- 1 (smallest)
- 6 (largest)
- 2
- 5
- 4

9. 2.8 Units of Volume
The space occupied by any sample of matter is called its volume
The volume of rectangular solids can be calculated by multiplying the length by width by height
Units are cubed because you are measuring in 3 dimensions
Volume of liquids can be measured with a graduated cylinder, a pipet, a buret, or a volumetric flask

10. 2.8 Units of Volume
A convenient unit of measurement for volume in everyday use is the liter (L)
Milliliters (mL) are commonly used for smaller volume measurements and liters (L) for larger measurements
1 mL = 1 cm3
10 cm x 10 cm x 10 cm = 1000 cm3 = 1 L

11. 2.8 Units of Volume

12. 2.8 Concept Practice
17. From what unit is a measure of volume derived?
A: Volume is a length measurement cubed.

13. 2.8 Practice
18. What is the volume of a paperback book 21 cm tall, 12 cm wide, and 3.5 cm thick?
A: 882 cm3 → 880 cm3; 8.8 x 102 cm3
19. What is the volume of a glass cylinder with an inside diameter of 6.0 cm and a height of 28 cm?
V=πr2h
A: 790 cm3; 7.9 x 102 cm3

14. 2.9 Units of Mass
A person on the moon would weigh 1/6 of his/her weight on Earth.
This is because the force of gravity on the moon is approximately 1/6 of its force of Earth.
Weight is a force – it is a measure of the pull on a given mass by gravity; it can change by location.
Mass is the quantity of matter an object contains
Mass remains constant regardless of location.
Mass v. Weight

15. 2.9 Units of Mass The kilogram is the basic SI unit of mass
It is defined as the mass of 1 L of water at 4°C.
A gram, which is a more commonly used unit of mass, is 1/1000 of a kilogram
1 gram = the mass of 1 cm3 of water at 4°C.

16. 2.9 Concept Practice
20. As you climbed a mountain and the force of gravity decreased, would your weight increase, decrease, or remain constant? How would your mass change? Explain.
A: Your weight would decrease; mass would remain constant.
21. How many grams are in each of these quantities?
a. 1 cg b. 1 μg c. 1 kg d. 1mg
A: g g g g

17. 2.10 Density
Density is the ratio of the mass of an object to its volume.
Equation → D = mass/volume
Common units: g/cm3 or g/mL
Example: 10.0 cm3 of lead has a mass 114 g
Density (of lead) = 114 g / 10.0 cm3 = 11.4 g/cm3
See Table 2.7, page 46

18. 2.10 Density
Density determines if an object will float in a fluid substance.
Examples: Ice in water; hot air rises
Density can be used to identify substances
See Table 2.8, page 46

19. 2.10 Concept Practice
22. The density of silver is 10.5 g/cm3 at 20°C. What happens to the density of a 68-g bar of silver that is cut in half?
A: Its density does not change.

20. 2.10 Concept Practice
23. A student finds a shiny piece of metal that she thinks is aluminum. In the lab, she determines that the metal has a volume of 245 cm3 and a mass of 612 g. Is the metal aluminum?
A: Density = 2.50 g/cm3; the metal is not aluminum.
24. A plastic ball with a volume of 19.7 cm3 has a mass of 15.8 g. Would this ball sink or float in a container of gasoline?
A: Density = g/cm3; the ball will sink.

21. 2.10 Specific Gravity (Relative Density)
Specific gravity is a comparison of the density of a substance to the density of a reference substance, usually at the same temperature.
Water at 4°C, which has a density of 1 g/cm3, is commonly used as a reference substance.
Specific gravity = density of substance (g/cm3)
density of water (g/cm3)
Because units cancel, a measurement of specific gravity has no units
A hydrometer can be used to measure the specific gravity of a liquid.

22. 2.11 Concept Practice
25. Why doesn’t a measurement of specific gravity have a unit?
A: Because it is a ratio of two density measurements, the density units cancel out.
26. Use the values in Table 2.8 to calculate the specific gravity of the following substances.
a. Aluminum b. Mercury c. ice A:

23. 2.12 Measuring Temperature
Temperature determines the direction of heat transfer between two objects in contact with each other.
Heat moves from the object at the higher temperature to the object at a lower temperature.
Temperature is a measure of the degree of hotness or coldness of an object.
Almost all substances expand with an increase in temperature and contract with a decrease in temperature
An important exception is water

24. 2.12 Measuring Temperature
There are various temperature scales
On the Celsius temperature scale the freezing point of water is taken as 0°C and the boiling point of water at 100°C

25. 2.12 Measuring Temperature
The Kelvin scale (or absolute scale) is another temperature scale that is used
On the Kelvin scale the freezing point of water is
273 K and the boiling point is 373 K (degrees are not used).
1°C = 1 Kelvin
The zero point (0 K) on the Kelvin scale is called absolute zero and is equal to -273°C
Absolute zero is where all molecular motion stops

26. 2.12 Measuring Temperature
Converting Temperatures:
K = °C + 273
°C = K - 273

27. 2.12 Concept Practice
27. Surgical Instruments may be sterilized by heating at 170°C for 1.5 hours. Convert 170°C to kelvins.
A: K = 170°C = 443 K
28. The boiling point of the element argon is 87 K. What is the boiling point of argon in °C?
A: °C = 87 K – 273 = -186°C

28. 2.13 Evaluating Measurements
Accuracy in measurement depends on the quality of the measuring instrument and the skill of the person using the instrument.
Errors in measurement could have various causes
In order to evaluate the accuracy of a measurement, you must be able to compare it to the true or accepted value.

29. 2.13 Evaluating Measurements
accepted value – the true or correct value based or reliable references
experimental value – the measured value determined in the experiment
The difference between the accepted value and the experimental value is the error.
error = accepted value – experimental value

30. 2.13 Evaluating Measurements
The percent error is the error divided by the accepted value, expressed as a percentage of the accepted value.
Percent Error = x 100
An error can be positive or negative, but an absolute value of error is used so that the percentage is positive
|error| AV

31. 2.13 Concept Practice
32. A student estimated the volume of a liquid in a beaker as 200 mL. When she poured the liquid into a graduated cylinder she measured the value as 200 mL. What is the percent error of the estimated volume from the beaker, taking the graduated cylinder measurement as the accepted value?
A: Percent Error = x 100 = 4%
|200 mL mL|
200 mL