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Welcome to Homeschool Connections! Chemistry Class 3.1 - Measurement and Their Uncertainty 3.2 - The International System of Units 3.3 - Conversion Problems 3.4 - Density THE INTERNATIONAL SYSTEM OF UNITS (SI) • Science (and the rest of the world) uses the metric system. • The International System of Units is based on the metric system. • The most commonly used SI units in chemistry are: 1. Meter 2. Kilogram 3. Kelvin 4. Second 5. Mole • Second is also commonly abbreviated as sec. • These need to be memorized! NON-SI UNITS • Sometimes non-SI are used because it is more practical. • In this class we will use SI units where appropriate and non-SI units when needed. • Examples of non-SI units we will use: Celsius, gram, milliliter, cubic centimeter…. METRIC SYSTEM PREFIXES These must be memorized! The underlined ones are the ones we will use most often. UNITS OF QUANTITY • In your textbook, see Tables 3.3 (p74), 3.4 (p75), and 3.5 (p76). This will help you visualize how big (or small) these units are. • Length – SI unit is a meter, also commonly used is centimeter (cm), millimeter (mm), and kilometer (km). • Volume – SI unit is a liter, also commonly used is milliliter and cubic centimeter. • 1 ml of water take up a volume of 1 cm3 (aka, 1 cc). LENGTH caliper • See Table 3.3 (p74) to help visualize length. • SI unit = meter • Other commonly used units: centimeter (cm), millimeter (mm), and kilometer (km). ruler VOLUME • See Table 3.4 (p75) to help visualize length. • SI unit = liter Graduated cylinder volumetric flask • Other commonly used units: milliliter (ml), and cubic centimeter (cm3). • 1 ml of water = 1 cm3 of water = 1 cc water • Because volume can change with temperature, is measured at a given temperature. pipet syringe MASS • See Table 3.5 (p76) to help visualize length. Scales (measure weight) • SI unit = kilogram (kg) • Other commonly used units: gram (g), and milligram(mg). • 1 ml of water = 1 cm3 of water = (about) 1 g • Weight is the force that pulls on a given mass by gravity. Balances (measure mass) TEMPERATURE • SI unit = Kelvin (K) Water freezes at 273.15 K Water boils at 373.15 K Absolute zero = 0 K • Also used: Celsius, aka, Centigrade (°C) Water freezes at 0°C Water boils at 100 °C Absolute zero = -273 °C • K = °C + 273 °C = K – 273 • Never used: Fahrenheit (°F) ENERGY • Energy is the capacity to do work or produce heat. • SI unit: Joule (J) • Also used: calorie (cal) • 1 calorie is the temperature of 1 gram of water 1°C. • 1 J = 0.2390 cal 1 cal = 4.184 J • Calorie is a nutritional measure of energy • 1 Calorie = 1000 calories (or 1 kcal) SAMPLE PROBLEM 3.4 (P78) Normal body temperature is 37°C. What is that temperature in K? Analyze: Temp in °C = 37°C K = °C + 273 Temp in K = ? Solve: K = °C + 273 = 37+ 273 = 310 K DIMENSIONAL ANALYSIS •Dimensional analysis use conversion factors. •Conversion factor: A ratio of equivalent numbers. Examples: CONVERSION FACTORS LARGE NUMBER small number small unit LARGE UNIT When you multiple a number by a conversion factor the number and unit changes but the actual size stays the same. QUESTION…. How many significant figures does a conversion factor have? An infinite number. DIMENSIONAL ANALYSIS Define: It is a way to analyze and solve problems using units (or dimensions) of the measurement. I require the use of dimensional analysis!!! SAMPLE PROBLEM 3.5 (P82) How many seconds are in a workday that lasts exactly 8 hours? Analyze: Time worked = 8 hour 1 hour = 60 minutes 1 minute = 60 seconds. Seconds worked = ? Solve: = 28,000 sec = 2.8 x 104 sec PRACTICE PROBLEM 28 (P82) How many seconds are there in an exactly 40 hour work week? Analyze: 60 minutes = 1 hour seconds in 40 hours= ? 60 seconds = 1 minute Solve: = 144000 sec = 1.44000 x 105 sec SAMPLE PROBLEM 3.6 (P83) The directions for an experiment asks each student to measure 1.84 g of copper (Cu) wire. The only copper that is available is a spool with a mass of 50 g. How many students can do the experiment before the copper runs out? Analyze: Mass of available copper = 50 g Each student needs 1.84 g Number of student that can do the experiment = ? SAMPLE PROBLEM 3.6 (P83) The directions for an experiment asks each student to measure 1.84 g of copper (Cu) wire. The only copper that is available is a spool with a mass of 50 g. How many students can do the experiment before the copper runs out? Analyze: Mass of available copper = 50 g Each student needs 1.84 g Number of student that can do the experiment = ? Solve: = 27.174 student = 27 students (You can not have part of a student – people come in wholes!) PRACTICE PROBLEM 30 (P83) An experiment required that each student use an 8.5 cm magnesium ribbon. How many students can do the experiment if there is only 570 cm length of magnesium ribbon available? Analyze: 570 cm magnesium ribbon available Each student needs 8.5 cm Number of students that can do the experiment = ? Solve: = 67.05882 students = 67 students PRACTICE PROBLEM 31 (P83) A 1.00 degree increase on the Celsius scale is equivalent to a 1.80 degree increase on the Fahrenheit scale. If the temperature increases by 48.0°C, what is the corresponding temperature increase on the Fahrenheit scale? Analyze: 1°C = 1.8°F Temp increase in °F = ? Temp increase = 48.0°C Solve: = 86.4 °F SAMPLE PROBLEM 3.7 (P84) Express 750 dg in grams. Analyze: Mass = 750 dg 1 g = 10 dg Mass in g = ? Solve: = 75 g PRACTICE PROBLEM 32 (P84) Using the tables from this chapter, convert the following. a. 0.044 km to m b. 4.6 mg to g c. 0.107 g to cg PRACTICE PROBLEM 33 (P84) Convert the following. a) 15 cm3 to liters l b) 7.38 g to kg kg c) 6.7 s to ms ms d) 94.5 g to µg SAMPLE PROBLEM 3.8 (P85) What is 0.073 cm in µm? Analyze: Length = 0.073 cm Length in µg = ? 102 cm = 1 m 1 m = 106 µm Solve: μm PRACTICE PROBLEM 34 (P85) The radius of a potassium atom is 0.227 nm. Express this in centimeters (cm). Analyze: Radius = 0.227 nm Radius in cm = ? Solve: 109 nm = 1 m 1m = 102 cm PRACTICE PROBLEM 35 (P85) The diameter of the Earth is 1.3 x 104 km. is the diameter expressed in decimeters? Analyze: Diameter = 1.3 x 104 km Diameter in dm = ? Solve: 1 km = 103 m 101 dm = 1 m SAMPLE PROBLEM 3.9 (P86) The mass per unit volume of a substance is called its density. The density of magnesium is 7.21 g/cm3. What is the density of magnesium expressed as kg/m3. Analyze: Density of Mg = 7.21 g/cm3 Density of Mg in kg/m3 = ? Solve: 103 g = 1 kg 106 cm3 = 1 m3 [(100*100*100) cm3 = 1 m3] PRACTICE PROBLEM 36 (P86) Gold has a density of 19.3 g/cm3. What is the density in kg/cm3? Analyze: Density of Au = 19.3 g/cm3 Density of Au in kg/m3 = ? Solve: 103 g = 1 kg 106 cm3 = 1 m3 PRACTICE PROBLEM 37 (P86) There are 7.0 x 106 red blood cells (RBC) in nm3 of blood. How many RBC are in 1.0 L of blood? Analyze: 7.0 x 106 RBC in 1 nm3 1 m3 = 106 cm3 103 ml = 1 L Solve: 1 m3 = 1021 nm3 1 cm3 = 1 ml RBC in 1.0 L = ? DENSITY Define: The ratio of the mass of an object to its volume. Is this a chemical or physical property? Physical DENSITY Does the density change with the amount of the substance you have? NO Is density an extensive or intensive property? Intensive Why? Because it depend only on the composition of the substance not on the size of the sample. DENSITY CHART Solids g/cm3 (at ~20°C) Liquids g/cm3 (at ~20°C) Copper 8.68 95% Sulfuric Acid 1.84 Cork 0.24 Bromine 3.12 Hickory (wood) 0.85 Citric Acid 1.66 Ice 0.92 Dawn Dish Soap 1.03 Iron 7.21 Ethanol 0.79 Ivory 1.84 Glycerin 1.26 Maple syrup 1.37 Honey 0.8 Paraffin (wax) 0.72 Iodine 4.93 Red Cedar (wood) 0.38 Methane 0.46 Rubber 1.52 Olive Oil 0.92 Styrofoam 0.005 Vinegar 1.01 Glass 2.58 DENSITY OF LIQUIDS – SMART EGG Which liquid is denser? Salt Water DENSITY AND TEMPERATURE What generally happens to density when the temperature increase? Density Decreases Why? Generally, as the temperature increases materials tend to expand – get bigger – increase volume. Their mass stays the same. So density decreases. What material is a VERY important exception to this? WATER SAMPLE PROBLEM 3.10 (P91) A copper penny has a mass of 3.1 g and a volume of 0.35 cm3. What is the density of the penny? Analyze: Mass = 3.1 g Volume = 0.35 cm3 Density = mass/volume Densitycopper penny = ? Solve: Density = mass/volume = 3.1 g / 0.35 cm3 = 8.8571 g/cm3 = 8.9 g/cm3 PRACTICE PROBLEM 47 (P91) A bar of silver has a mass of 68.0 g and a volume of 6.48 cm3. What is its density? Analyze: Mass = 68.0 g Volume = 6.48 cm3 Density = mass/volume Densitysilver= ? Solve: Density = mass/volume = 68.0 g / 6.48 cm3 = 10.49382 g/cm3 = 10.5 g/cm3 PRACTICE PROBLEM 46 (P91) A student find a shiny piece of metal that she thinks is aluminum. In the lab, she determines that its mass is 612 g and its volume is 245 cm3. Is it aluminum? Analyze: Mass = 612 g Volume = 245 cm3 Density = mass/volume Densitymetal= ? Solve: Density = mass/volume = 612 g / 245 cm3 = 2.49796 g/cm3 = 2.50 g/cm3 The density of aluminum is 2.70 g/cm3, the density of this metal is 2.50 g/cm3, therefore this metal is NOT aluminum. SAMPLE PROBLEM 3.11 (P92) What is the volume of a pure silver coin that has a mass of 14 g? The density of pure silver (Ag) is 10.5 g/cm3. Analyze: Mass = 14 g Densitysilver= 10.5 g/cm3 Density = mass/volume Volume = ? Solve: Density = mass/volume volume = mass/density = 14 g /10.5 g/cm3 = 1.3333cm3 = 1.3 g/cm3 Ag PRACTICE PROBLEM 48 & 49 (P92) 48. Using dimensional analysis and the given densities to make the following conversions. 49.Rework the previous problem using: density = mass/volume PRACTICE PROBLEM 48 & 49 (P92) a) 14.8 g of boron to cm3. Density of boron = 2.34g/cm3. Analyze: massboron = 14.8 g densityboron= 2.34g/cm3 cm3boron = ? density = mass/volume Solve (48): = 6.234786 cm3 = 6.23 cm3 boron Solve (49): Density = mass /volume volume = mass/density PRACTICE PROBLEM 48 & 49 (P92) a) 4.62 g of mercury (Hg)to cm3. Density of mercury = 13.5 g/cm3. Analyze: massmercury = 4.62 g densitymercury= 13.5 g/cm3 cm3mercury = ? density = mass/volume Solve (48): = 0.342 cm3 Hg Solve (49): Density = mass /volume volume = mass/density CHEM CLASS Read: Ch. 1 Read: Ch. 2 Ch. 1 HW due Ch. 1 Quiz due Read: Ch. 3 Ch. 2 HW due Ch. 2 Quiz due Labor Day Image: www.wilsoninfo.com Read: Ch. 4 Ch. 3 HW due Ch. 3 Quiz due CHEM CLASS Review: 1-4 TEST #1 Ch. 4 HW due Ch. 4 Quiz due TEST #1 DUE Read: Ch. 5 Read: Ch. 6 Ch. 5 HW due Ch. 5 Quiz due Read: Ch. 7 Ch. 6 HW due Ch. 6 Quiz due Halloween Image: www.schoolclipart.biz CHEM LAB VIEW: Introduction to Chemistry, and Lab Safety VIEW: The Scientific Method & Lab Reports Lab Safety WS due VIEW: Accuracy & Precision The Scientific Method & Lab Reports WS due Labor Day Image: www.wilsoninfo.com NO New Lab Accuracy & Precision Lab Report due CHEM LAB NO New Lab VIEW: Atomic Emission Spectra VIEW: Periodic Trends Atomic Emission Spectra Report due VIEW: Electroconductivity of Solutions Periodic Trends WS due Halloween Image: www.schoolclipart.biz