The International System of Units( SI)
Prefixes in SI system
Multiple Prefix Symbol 10
-12 pico p
10-9 nano n
10-6 micro µ
10-3 milli m
10-2 centi c
10
-1 deci d 10 deca da 10 2 hecto h 10 3 kilo k 10 6 mega M 10 9 giga G
10
12 tera T
Mass and Weight-- Mass of a substance is the amount of matter present in it while weight is the force exerted by gravity on an object. The mass of a substance is constant whereas its weight may vary from one place to another due to change in gravity. The mass of a substance can be determined very accurately by using an analytical balance
Volume-- Volume has the units of( length) 3. So volume has units of m 3 or cm 3 or dm 3. A common unit, litre( L) is not an SI unit, is used for measurement of volume of liquids. 1 L = 1000 mL, 1000 cm 3 = 1 dm 3
Density: Density of a substance is its amount of mass per unit volume. SI unit of density = SI unit of mass / SI unit of volume = kg / m 3 or kg m – 3 This unit is quite large and a chemist often expresses density in g cm – 3.
Temperature--There are three common scales to measure temperature— ° C( degree celsius), ° F( degree Fahrenheit) and K( kelvin). Here, K is the SI unit.