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1 The International System of Units, or the SI Units Vs. Honors Chem 1 LENGTH In the SI, the base unit of length is the Meter. Prefixes identify additional units of length, based on the meter. Smaller than 1 meter: CONVERSIONS OF METERS 1000 (10 3 ) millimeters = 1 meter 100 (10 2 ) centimeters = 1 meter 10 (10 1 ) decimeters = 1 meter Larger than 1 meter: 10 meters = 1 decameter 100 (10 2 ) meters = 1 hectometer 1000 (10 3 ) meters = 1 kilometer Honors Chem 2 Factor-Label Method for Conversions We need to be able to convert between units. We can use Dimensional Analysis, or the Factor-Label Method, to convert between different metric units, or perhaps from metric to English. The Factor-Label method uses Unit Factors which do the converting for you. Factor-Label Method for Conversions Let s use a simple example to illustrate the Factor-Label method. How many donuts are in 3.5 dozen We would ordinarily say that there are 12 donuts in a dozen or 12 donuts = 1 dozen donuts What does any number divided by itself equal to Honors Chem 3 Honors Chem 4 Honors Chem 5 Honors Chem 6 1

2 Honors Chem 7 LENGTH Let s try reversing the conversions that we just spoke of: CONVERSIONS OF METERS Smaller than 1 meter: 1 millimeter = 10-3 Meter 1 centimeters = 10-2 Meter 1 decimeters = 10-1 Meter Larger than 1 meter: 1 meters = 10-1 Decameter 1 meters = 10-2 Hectometer 1 meters = 10-3 Kilometer Honors Chem 8 Another Example: Using the statement that 1 inch equals 2.54 centimeters, convert the following: 5280 ft = kilometers LENGTH Convert these metric lengths using the factor- label method km = m 11.9 x m = 56 mm Unit factors do not affect sig figs, only measured values do. 62 cm = 0.62 m 710 mm = 0.71 m 0.48 km = 4.8 x 10 4 cm 121 mm = 1.21 x 10-4 km 5280 has 3 Sig Fig s, so the answer should be 1.61 km. Honors Chem 9 Honors Chem 10 Here are the Conversions that you ll need to know Prefix S.I. PREFIXES Symbol Amount mega M 1,000,000 (10 6 ) kilo k 1,000 (10 3 ) hecto h 100 (10 2 ) deca da 10 (10 1 ) deci d 0.1 (10-1 ) centi c 0.01 (10-2 ) milli m (10-3 ) Micro U (10-6 ) Nano n (10-9 ) Honors Chem 11 Let s Take a Look at Mass Is there a Difference between Mass and Weight o Chemistry is the study of matter o Matter is defined as anything that has mass and takes up space. o We found that describing space begins with measuring length. o In the same way, describing matter begins with measuring mass. o Mass is a measurement of how much matter is present. Honors Chem 12 2

3 Let s 10 g 5 g Balance Or Scale Let s look at the devices used to measure mass and weight and see if we can discover the difference. When The object the pans to be balance measured you know is Mass placed you is measured have in one the pan. same with The a amount other device pan of called matter is loaded a balance on with each side. mass In units this until case, the the two mass of pans the balance object is 15 grams 10 g 5 g MASS What s the Difference WEIGHT Sample Problems So, Mass is a measure of how much matter is present Balance Honors Chem 13 Honors Chem 14 Let s look at the devices used to measure mass and weight and see if we can discover the difference. One The Weight thing object that to be measured is is determines measured the reading placed on the platform. scale is the The amount of weight stuff with of we a the device put object on the called pushes platform. a the In platform other scale. words, down which weight moves is the determined arrow along in the part scale. by mass. To find the other component of weight we need to take a trip to the moon. The reading pull of gravity on the is scale less would on the be Moon If What What it was would would balanced happen happen on if Earth if we we put put then it scale different therefore because the weight gravity of the is different object is will on our the remain balance moon balanced on Would the on moon we the still Moon get the from less on the the Moon Moon to than Earth. it is Weight on Earth. is a because same Would value there it still for is the be still balanced weight the same (Remember measure Mass stayed amount the mass not of hasn t matter only the same changed) of in the because each mass pan. but it is also just how a measure hard gravity of the pulls amount on of the matter mass. and that didn t change. 10 g 5 g Weight is determined by mass and Scale Weight is determined by mass and the pull of gravity Honors Chem 15 Honors Chem 16 What is the mass of 5000 kg spacecraft on the moon. Gravity on the Moon is 1/6 that of Earth. Α 5000 kg. Kilograms are a measure of mass and mass does not change. A spacecraft on earth weighs 30,000 lb. What is the weight of the spacecraft on Pluto. Gravity on Pluto is 1/15 that of Earth. Α 2000 lb. Pounds are a measurement of weight and weight changes depending on gravity. 1/15 x 30,000 = 2000 Honors Chem 17 MASS In the Metric System the base unit of Mass is the Gram. Prefixes identify additional units of Mass. The S.I. Prefixes are used to identify larger/smaller quantities of the grams: CONVERSIONS OF METERS Smaller than 1 meter: 1,000,000,000 (10 9 ) nanogram = 1 gram 1,000,000 (10 6 ) microgram = 1 gram 10 (10 3 ) milligram = 1 gram Larger than 1 meter: 10 grams = 1 decagrams 100 (10 2 ) grams = 1 hectograms 1000 (10 3 ) grams = 1 kilograms Honors Chem 18 3

4 MASS Convert these metric masses using the factor-label method kg = g kg = mg x 10 2 VOLUME In the SI, the base unit of volume is the Liter. Prefixes identify additional units of length, based on the liter. Volume is derived from the length measurement cubed cubed. 62 mg = g g = kg g = 4.8 x 10 3 ug 820 ng = 8.2 x 10-7 g 0.08 ug = 8 x 10-5 mg 15.6 ug = 1.56 x 10 4 ng COMMON CONVERSIONS OF VOLUME 1,000,000 (10 6 ) microliters (ul) = 1 Liter (L) 1000 (10 3 ) milliliters (ml) = 1 Liter (L) 1 cm 3 = 1 ml Honors Chem 19 Honors Chem 20 VOLUME Convert these metric volumes using the factor- label method. Be mindful of Significant Figures ml = 3.09 x 10-2 L 0.89 L = 890 cm ul = 0.85 ml Honors Chem 21 What s the Difference Between Temperature and Heat An object s thermal energy or heat is determined d by the sum of the energies of all the particles is a substance. Temperature is a measurement of the average energy of the particles in substance. The following example will better explain the difference. Honors Chem 22 What s the Difference Between Temperature and Heat Heat Let s Now Water The Which water is let s heat boils the container record up particles sum at a 100 C. large of do the in you and temperatures energies each Since think small container both has of all containers more of the have thermal particles water of water are in in a on each boiling energy same substance. a hot container. average (heat) both plate Since containers until energy. there both have containers are more the same water begin temperature. particles to boil in the large container there is more heat as well. 100 C 100 C Less Heat More Heat Temperature is a measurement of the average energy of the particles in substance. Temperature is measured on a scale called a thermometer. There are three different temperature scales currently used to measure temperature. Fahrenheit, Centigrade, and Kelvin Let s compare the three scales side by side. Honors Chem 23 Honors Chem 24 4

5 A temperature scale must have a point to call zero. Record two temperatures. Water Boils 373 K 100 C 212 F One On difference the Centigrade Fahrenheit Kelvin between scale, the scale, zero three is zero the scales is point the is that they freezing where all have there point a different is of no pure starting saturated water. heat: (zero) Absolute salt point water. Zero 0 C 0 F 0 K Kelvin Centigrade Fahrenheit Honors Chem 25 Water Freezes The How Freezing This Compare Fahrenheit second first means many to 100 degrees boiling temperature that to Fahrenheit the 180. are on of degrees is change the 5/9 the is K the boiling is and on Fahrenheit degrees size freezing the C from of scales Kelvin 100 point are freezing scale smaller = both of and or of 10 pure represents Centigrade to = than boiling water 5 on 100 scales 180 Kelvin degrees each degrees are and 180 scale the Centigrade of same 18 change. size. 9 degrees K 0 C 32 F Kelvin Centigrade Fahrenheit Honors Chem 26 If the temperature goes up 3 on the Centigrade scale, how far does it rise on the Kelvin scale If the temperature goes up 3 on the Fahrenheit scale, how far does it rise on the Centigrade scale A.) More than 3 B.) B) 3 C.) Less than 3 Α B.) 3 Centigrade degrees are the same size as Kelvin degrees. Water Boils Water Freezes K 273 K 100 C C 212 F 32 F A.) More than 3 B.) B) 3 C.) Less than 3 Α C.) Less than 3 For every 1 o F, there are 5/9 o C. Water Boils Water Freezes 373 K 273 K 100 C C 212 F 32 F Kelvin Centigrade Fahrenheit Honors Chem 27 Kelvin Centigrade Fahrenheit Honors Chem 28 Now that you understand the differences between the three temperature scales we will make some temperature conversions. The formulas are listed below. Copy them down so you can refer to them. K = C C = K C = 5/9( F 32 ) F = 9/5 C + 32 Conversions Make the following temperature conversions then click to see the answers. C = 5/9(F 32) F = 9/5 C + 32 K = C C = K K = C F = C C = F C = K K = C F = C C = F C = K 265 Honors Chem 29 Honors Chem 30 5

6 Factor Label Worksheets (2) o An important relationship between an object s Mass and Volume is called. o Density is the ratio of the mass of an object to it s volume: Density = mass/volume i.e. A 10.0 cm 3 piece of lead has a mass of 114 grams. What is the density Density = 114 g/10.0 cm 3 = 11.4 g/cm 3 Honors Chem 31 Honors Chem 32 o Remember, Density is an Intensive, Physical Property; Here are the densities of some common substances: Density Material (gm/cm 3 ) Density Solids Density Material Material (gm/cm (gm/cm 3 ) 3 ) Magnesium 1.7 Gases at STP Liquids Aluminum 2.7 Air Water at 4 C Copper Carbon dioxide Water at 20 C Gold 19.3 Carbon Gasoline 0.70 Iron monoxide Mercury 13.6 Lead 11.3 Hydrogen Milk 1.03 Platinum 21.4 Helium Uranium 18.7 Nitrogen Osmium 22.5 Ice at 0 C 0.92 Honors Chem 33 o A material s Density will determine whether it will sink or float in another material. o A Less dense material will float on a material with greater density. Conversely, a material with greater density will sink through a material with less density. o Let s check out the Density Simulated Experiment on Chem ASAP, Chapter 3, Simulation 1 D:\ChemASAP.exe Honors Chem 34 o Can we determine the Density of an object graphically o In an experiment, groups of 5, 10, 15, 20, and 25 pennies of pre & post 1982 were weighed for mass, along with their corresponding volumes. o Pre 1982 pennies were made of copper, while post pennies were made of zinc, with a copper covering. o Both pennies occupy the same volume. o Which are more dense Let s find out Honors Chem 35 Density of Pennies Number Pre 1982 Pre 1982 Post 1982 Post 1982 of Pennies Mass Volume Mass Volume Which Pennies are Heavier How is the Density determined from the graph Which Pennies have a greater Density Density pre1982 = ( )/( )/( ) 55.2) = 8.46 Density post1982 = ( )/( )/( ) 55.4) = 7.92 Density of Pennies Honors Chem 36 Mass (gms) Volume (ml) Pre 1982 Post 1982 Linear (Post 1982) Linear (Pre 1982) 6

7 Specific gravity Specific gravity = density of object(g/ml) density of water (g/ml) Specific gravity is unitless. Normally use 1.00 g/ml for density of water. Density problems A lead sphere has a mass of 1.20 x 10 4 g and a volume of 1.05 x 10 3 cm 3. Calc the density of lead. What volume, in liters, will 8.00 x 10 2 g of air occupy if the density of air is 1.29 g/l What is the mass, in grams, of a femur (leg bone) having a volume of 118 cm 3 The density of bone is 1.8 g/cm 3 Honors Chem 37 Honors Chem 38 Density Worksheets (2) Honors Chem 39 7