Measurements The “inch-pounds” or customary unit measurement system has been used in the US for as long as we can remember. We, the US, are one of the only countries that has no fully adopted the SI, International System of Units, or metric unit measurements. Many believe that the metric system is a much easier system to use. The SI system is what is ALWAYS used in chemistry (all sciences) because it allows of universal communication.

Measurements We use measurements in everyday life and in science A measurement includes both a value and a unit Measurements represent quantities – a quantity is something that has magnitude, size, or amount. There are both qualitative measurements and quantitative measurements It takes a long time to walk home from school It took me 2 hours and 14 minutes to walk home from school

Common Measurements Mass Weight Length Volume The quantity of matter an object contains SI Unit for Mass is kg Weight force – measure of pull on the mass of an object due to gravity We not really talk about the “weight” of objects in chemistry! Length SI Unit for length is m Volume the space occupied by a sample of matter volume changes when temperature changes V = l x w x h SI Unit for volume is L 1L = 1dm3 1mL = 1 cm3 = 20 drops Mass of a human on Earth and the Moon is the same. Kg = kilogram 1kg = 1000g Weight of a human on Earth is greater than the weight of a human on the Moon. 60kg on Earth = 10kg on Moon Length – the distance between two locations (start, stop) Volume = length x width x height (cube or rectangle) Volume can be measured by using a beaker (like a cup), graduated cylinder (tall and skinny), or Erlenmeyer flask (skinny neck and wide bottom)

Common SI Information 1 penny is exactly 2.5 grams 1 nickel is exactly 5 grams A doorknob is about 1 meter from the ground 1 milliliter is the same volume as 1 cm3 1 milliliter of water has a mass of 1 g 1 liter of water has a mass of 1 kg

Density Density is the mass of an object in a given space Typically density will decrease if the volume and temperature of an object increase and visa-versa. NOT TRUE for water! Density = mass ÷ volume Units: g/ml or g/cm3 Different types of matter have different densities: More mass in a smaller volume = more dense Less mas in a greater volume = less dense More dense solid - sinks in its own liquid Less dense solid – floats in its own liquid Density is a physical property that varies with temperature (if the temperature goes up then usually the volume goes up and the density goes down and visa-versa) Water: When the molecules of water freeze, they become crystals. The crystals create space within and between them, making them less dense than their liquid molecules which are constantly touching on all sides. Examples: Helium is less dense the air so balloons float Ice water is less dense than water so ice floats in water (or most liquids)

Calculations & Conversions Conversion Factor – any fraction or ratio in which the numerator equals the denominator. When two numbers are equal their ratio will be one. 1 foot = 12 inches is the same as writing 1 foot/12 inches or 12 inches/1 foot 3200 g x (conversion factor 1 kg/1000g) = 32Kg Dimensional Analysis – using the conversion factor to change on unit into another unit. Convert 36 inches into feet. 36 inches x 1 foot = 3 feet 1 12 inches

SI Prefixes We are really only going to be looking from Mega (M) down to Pico (p) for this class. Prefix maintains its meaning regardless of the type of measurement to which it is connected. 1 kilogram = 1000 grams Work on Metric Mania – 15-20 minutes Move on the Dimensional Analysis 1 kilometer = 1000 meters 1 kiloliter = 1000 liters Metric Mania Worksheet as a group! The prefixes is connected to the measurement to express very large or very small numbers. Where the - - is can have any of the base units of gram (mass), meter (length), or liter (volume)

Work independently or at your table group to complete the front side! Metric Mania Wkst Work independently or at your table group to complete the front side!

SI Units and Variables for various measurements Symbol Other Units Symbols Length l Meter m Mass kilogram kg Time t second s Hour, minute hr, min Temperature T Kelvin K Celsius °C Amount/count n mole mol Volume v Cubic meter cm3 Liter L = dm3 Energy E Joule J Calorie cal Pressure P Pascal Pa Kilopascal Atmosphere kPa atm Density D grams/cubic centimeter g/cm3 Grams/millimeter g/ml SI Units and Variables for various measurements

Dimensional Analysis Multiple Step Problems – more than 1 conversion factor Given (con. factor) (con. factor)(con. factor) = want Convert 15 days into minutes 15 days x 24 hours x 60 mins = 21,600 mins 1 1 day 1 hour How many hours are in a year? hrs_ year Units that you want to cancel go in the the denominator of the conversion factor. Always put the given number and units that you are changing over 1. If going from a larger unit to a smaller unit, the number will increase. If going from a smaller unit a larger unit, the number will decrease. Always write the units along with the number in the problem and conversion factor so you can see which units will cancel! What do you think you need to know? Hours per day 24 hrs/1 day Days per week 7 days/ 1 week Weeks in a month 4 weeks/ 1 month Months in a year 12 months/1 year Cross out anything on the top and bottom do the math…8064 hrs/1 year

Try this one! If you are going 50 miles per hour, how many feet per second are you traveling? Hint: 5280 feet / 1 mile 50 miles/ 1 hour x 5280 ft/ 1 mile x 1 hr / 60 minutes x 1 min / 60 seconds = 73.3 ft/sec