In recording measurements, it is necessary to understand 1. SIGNIFICANCE of numbers 2. importance of UNITS.

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1 CHEMISTRY IS LARGELY A QUANTITATIVE SCIENCE Theories and ideas are tested by measurement Measurements are usually quantitative have numbers Science is built on a foundation of mathematics. In recording measurements, it is necessary to understand 1. SIGNIFICANCE of numbers 2. importance of UNITS.

2 Learning Objectives about Units 1. Understand importance of units in measurement 2. Identify common metric units 3. Apply common metric prefixes 4. Use simple unit conversions

3 Systems of measurements: the old English System - what the United States uses today derived from the 'Kings" feet (Old England). Also known as the United States Customary System (USCS) Units 1 foot ( big feet") 1 inch (knuckle) 1 yard (King Henry I - nose to thumb)

4 System Internationale (S.I.): the new The creation of the decimal Metric System at the time of the French Revolution and the creation of two platinum standards representing the meter and the kilogram was the first step in the development of the present International System of Units. Science has adopted the S.I. When we say metric we mean S.I.

5 Compare and contrast:

6 Know one s units Not only inexperienced chemistry students can be confused by units Whoops!

7 Time waits for no one

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9 Remember these: case is important compare M and m mega- (M) 1,000, kilo- (k) 1, deci- (d) 1/ centi- (c) 1/ milli- (m) 1/1, micro- ( ) 1/1,000, nano- (n) 1/1,000,000,

10 The seven fundamental (base) units of the S.I. Physical property Name of unit Symbol Length meter m Mass kilogram kg Time second s Electrical current ampere A Temperature kelvin K Luminous intensity candela Cd Amount of substance mole mol

11 Length: meter (m) Length is fundamental unit. In metric system, meter is standard unit. Original physical standard meter is kept in Paris. Modern definition: Length of path travelled by light in vacuum during a time interval of 1/ of a second It equals inches. 1m = 100 cm then 1 inch = 2.54 cm. Comparisons: centimeter - width of your fingernail kilometer miles millimeter - thickness of a dime

12 Mass: kilogram (kg) Mass is fundamental unit; it measures quantity of matter present. Although mass and weight are used interchangeably in conversation, mass and weight have different meanings. Weight includes effect of gravity on mass. In a space capsule, your weight would be zero (absence of gravity) but your mass is same as on earth. Standard unit of mass is kilogram (kg). Conversions factors: 1 pound = 454 g 2.2 pounds (lb) = 1 kilogram (kg) 1 gram (g) = 1000 milligrams (mg) or 1 mg = g 1 kilogram (kg) = 1000 grams (g) or 1 g = kg

13 Volume Volume is derived unit (using length units). It measures space. Standard unit of measurement is meter cubed (m 3 ) or centimeter cubed (cm 3 ). Note: In chemistry, standard unit of volume for liquid is the liter (L) not strictly S.I. The liter is similar to a quart in the English system. Conversion factors: 1 liter (L) = 1.06 quarts (qt) 1 quart (qt) = liters (L) 1 liter (L) = 1000 milliliters (ml) or 1 milliliter (ml) = liter (L) 1 milliliter (ml) = 20 drops 1 milliliter (ml) of water = 1 cm 3. (or 1 CC)

14 Relationship between cm 3 and ml 1 L = 1 dm 3 ; 1 dm = 10 cm; 1 dm 3 = 10 3 cm 3 ; 1 L = 1000 ml; 1 ml = 1 cm 3

15 Derived units Derived units can be resolved into combinations of two or more fundamental units Area and volume involve only the units of length Most involve combinations of different units Quantity Units Area m 2 Volume m 3 Density kg/m 3 Speed m/s Force kg m/s 2 (newton N) Pressure kg/(m s 2 ) (pascal Pa) Energy kg m 2 /s 2 (joule J)

16 Dimensions and relations between units It is important to keep track of dimensions in derived units when making conversions: 1 cm = 10 mm 1 cm 2 = 10 x 10 = 100 mm 2 1 cm 3 = 10 x 10 x 10 = 1,000 mm 3

17 Conversion factors and unit factors Making conversions between different units is very important Always keep track of units in calculation Conversion factor: 1000 mg = 1 g Unit factors 1 gmg mg 1g 1 There are two unit factors for any conversion

18 Unit factors at work How many grams are there in 2680 mg of sucrose? Conversion factor: mg = 1 g Unit factor 1g mg? g = amount in mg x unit factor 1g? g 2680 mg x 1000 mg Unit factor has value of 1 no change in value Unit factor causes old units to cancel 1g? g 2680 x 2.680g 1000

19 Handy conversions

20 Working with unit conversions

21 Density Mass divided by volume Units are: g/cm 3 (solid) g/ml (liquid) kg/m 3 or g/l(gas)

22 Density and temperature In most cases, the density of a substance decreases with temperature. (Why is that?) Water provides a critical exception to the rule

23 Working with densities