The SI System of Measurement

The Nature of Measurement

Part 1 - numberPart 2 - scale (unit)

Examples:20 grams

6.63 x 10-34 Joule·seconds

A Measurement is a quantitative observation consisting of TWO parts

Derived SI UnitsCombinations of SI base units form derived units.pressure is measured in kg/m•s2, or pascals

SI PrefixesCommon to Chemistry

Prefix Unit Abbr. ExponentKilo k 103

Deci d 10-1

Centi c 10-2

Milli m 10-3

Micro 10-6

Metric ConversionsgmL 10-1 10-2 10-3101102103

Baseunit

deci centi millidekahectokilo

Conversions in the metric system are merely a matter of moving a decimal point. The “base unit” means the you have a quantity (grams, meters, Liters, etc without a prefix.

Metric ConversionsgmL 10-1 10-2 10-3101102103

Baseunit

deci centi millidekahectokilo

Example #1: Convert 18 liters to milliliters

18 L1 2 3

18 liters = 18 000 milliliters

Metric ConversionsgmL 10-1 10-2 10-3101102103

Baseunit

deci centi millidekahectokilo

Example #2: Convert 450 milligrams to grams

123450 mg450 mg = 0.450 g

Metric ConversionsgmL 10-1 10-2 10-3101102103

Baseunit

deci centi millidekahectokilo

Example #3: Convert 20 kilograms to milligrams

20 kg 1 2 3 4 5 6

20 kg = 20 000 000 mg

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

4 quarters 1 dollar1 11 dollar 4 quarters

0.25 dollar 1 quarter1 11 quarters 0.25 dollar

Conversion Factors, continued

Dimensional analysis is a mathematical technique that allows you to use units to solve problems involving measurements.

4 quarter? quarters 12 dollars 48 quarters1 dollar

quantity sought = quantity given × conversion factor

example: the number of quarters in 12 dollars

number of quarters = 12 dollars × conversion factor

Factor Name Symbol1024 Yotta Y1021 Zetta Z1018 Exa E1015 Peta P1012 Tera T109 Giga G106 Mega M103 Kilo k102 Hecto h101 Deka da

Factor Name Symbol10-1 Deci d10-2 Centi c10-3 Milli m10-6 Micro μ10-9 Nano n10-12 Pico p10-15 Femto f10-18 Atto a10-21 Zepto z10-24 Yocto y

Using Conversion Factors

Conversion Factors, continuedSample Problem B Express a mass of 5.712 grams in milligrams and in kilograms.

Conversion Factors, continuedSample Problem B SolutionExpress a mass of 5.712 grams in milligrams and in kilograms.

Given: 5.712 gUnknown: mass in mg and kgSolution: mg

1 g = 1000 mg

Possible conversion factors:

1000 mg 1 gand

g 1000 mg

1000 mg5 5. 7712 g mg

12 g

1 kg5.712 g1000

0.005g

712 kg

Sample Problem B Solution, continuedExpress a mass of 5.712 grams in milligrams and in kilograms.

Given: 5.712 gUnknown: mass in mg and kgSolution: kg

1 000 g = 1 kg

Possible conversion factors:

Conversion Factors, continued

1000 g 1 kgandkg 1000 g