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.

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

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)

System Internationale (S.I.): the “new” 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.

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

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,

The seven fundamental units of measurement Physical propertyName of unitSymbol Lengthmeterm Masskilogramkg Timeseconds Electrical currentampereA TemperatureKelvinK Luminous intensitycandelaCd Amount of substancemolemol

Length: meter (m) Length is fundamental unit. In metric system, the meter is a the standard unit for measuring length. It is a little longer than a yard. The standard unit of metric length is kept in Paris. It is equal to inches. Since the meter is equal to 100 centimeters (cm), then 1 inch is equal to 2.54 cm. Comparisons: centimeter - width of your fingernail kilometer miles millimeter - thickness of a dime

Mass: kilogram (kg) Mass is a fundamental unit - measure of quantity of matter present Mass and weight are used interchangeably in normal conversation, mass and weight actually have different meanings Weight includes effect of gravity on mass In a space capsule: weight would be zero (absence of gravity) mass would be the same value as it was 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

Volume Volume is a derived unit (using length units). It is a measure of space. In simple terms, it is a measure of three (3) length units in three dimensions (breadth, length and width). The standard unit of measurement is the meter cubed (m 3 ) or the centimeter cubed (cm 3 ). In chemistry, volume is typically measured for a liquid. The standard unit of measurement for a liquid is the liter (L). 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 At room temperature, 1 milliliter (mL) of water = 1 cm 3. (or 1 CC)

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

Dimensions It is important to keep track of the dimensions in derived units. All the more when making conversions: 1 cm = 10 mm 1 cm 2 = 100 mm 2 1 cm 3 = 1,000 mm 3

Conversion factors Making conversions between different units is very important Always keep track of the units Make use of unit factors There are 1000 mg in 1 g (conversion factor) 1000 mg/1 g = 1; 1 g/1000 mg = 1 (unit factors) There are two unit factors for any conversion

Unit factors at work How many grams are there in 2680 mg of sucrose? We know there are mg in 1 g 1 g/1000 mg = 1 (unit factor) ? g = amount in mg x unit factor ? g = 2680 mg x 1 g/1000 mg = g Unit factor has value of 1 – no change in value Application of unit factor causes old units to cancel Never forget to show units of any measurement – unless it is a unit-less quantity

Handy conversions

Working with unit conversions

Density Mass divided by volume Units are: g/cm 3 (solid) g/mL (liquid) g/m 3 (gas)

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