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STEP 1 IN THE ROAD TO UNDERSTANDING CHEMISTRY Measurements & Ratios

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Compare your density to the metals on the Periodic Table Identify your solid on the Periodic Table

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Measuring with a Metric Ruler Special notes: Always start on the zero line, not the end of the ruler Always write down the last used number on the ruler Estimate 1 digit between mm lines (if it is exactly on the line then that next digit is 0) 12345 cm 6 0 Length of Bar 3.2 cm + estimate between marks = 3.23 cm 3.20 3.30

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Sample Measurements Length of bar 11.2 cm = 11.20 cm (right on line) Length of Bar 10.2 + estimate = 10.26 cm cm 1234567891011121314151617 0 cm 1234567891011121314151617 0 Let’s Practice to check your skills

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Using Length to Calculate Volume The amount of space an object takes up Volume Units: cm 3 (cm cm cm), cubic cm (cc), mL All of the above units are equal May also use any distance unit that is cubed Formulas Prism Volume = Base Area prism height* For a rectangular prism (box) this means l w h* For a triangular prism this means ½ b h h* For a cylinder this means r 2 h* Sphere Volume = 4/3 radius 3 or 4/3 circle area r

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Box Dimensions Calculations Side measurements l = 4 m, w= 2 m, h = 3 m V= l w h V = 4 m 2 m 3 m V = 24 m m m V=24 m 3 Practice Volume of Rectangular Prism (Box) Side A 3 m 2 m 4 m

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Box Dimensions Calculations Get sides in same unit (convert all to cm) l = 1 m = 100 cm, w= 30 cm (keep this one), h = 400 mm = 40 cm V= l w h V = 100 cm 30 cm 40 cm V = 120 000 cm cm cm V=120 000 cm 3 Practice Volume of Rectangular Prism (Box) Side A 400 mm 30 cm 1 m Note: All sides must be in the same unit Let’s Practice

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Calculations r = 10 cm h = 5 cm V= base area · height V = · r 2 · h V = 3.14 · (10 cm) 2 · 15 cm V= 3.14 · 100 · 15 cm 2 ·cm V = 4710 cm 3 Practice Volume of Cylindrical Prism (Box) Note: All measurements must be in the same unit Let’s Practice Box Dimensions 10 cm 15 cm

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Calculations r = 5 cm V= 4/3 · · r 3 V = 4/3 · 3.14 · (5 cm) 3 V = 4/3 · 3.14· 125 cm 3 V = 523.3 cm 3 Practice Volume of Sphere (Ball) Note: Moving to circles Box Dimensions 5 cm How would you solve this if all you had was a C = 31.4 cm C = 31.4 cm

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Calculations C = 31.4 cm 1. First find r r =C/2 = 31.4 cm/6.28 = 5 cm 2. Plug r into the formula V = 4/3 · 3.14 · (5 cm) 3 V = 4/3 · 3.14· 125 cm 3 V = 523.3 cm 3 Practice Volume of Sphere (Ball) What happens if you can’t measure radius? Let’s Practice Box Dimensions 5 cm C = 31.4 cm

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Liquid Volume Measuring always use a graduated cylinder to measure liquid volume do NOT use a beaker or flask to accurately measure liquid volume (only approximate ) estimate one decimal place beyond what is marked on the graduated cylinder (like ruler) Watch your scale markings (what is each line worth) Meniscus: curved surface of a liquid in a tube Measure the liquid at the bottom center of the lower curve of the meniscus (bdc) at eye level Note: some plastic cylinders don’t curve the water on Level Surface at Eye Level

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Check your skills Activity: Take a graduated cylinder, put some water in it & draw in your notes what the top of the water looks like in the cylinder Measure liquid level here Let’s Practice

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Fill Displacement If the object is hollow you can fill the object with water and measure the amount of liquid What do you do about the side thicknesses? If the object is solid or can’t hold water Fill a container to the brim with water Put object in the water Measure the water that comes out of the container What do you do about floating objects? Using Liquids to Measure Volume

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Comparing Volume and Mass Your task – find the mass of water for at least 5 different volumes. Required Record all measurements with accuracy and precision in a Data Table (exacts – no “about” measurements) Graph the volume and mass of the water on Excel Graph & compare to given data of Ethanol & print 2 graphs Volume of Ethanol (mL)Mass of Ethanol (g) 20.015.78 42.533.53 66.052.07 79.362.57 99.978.82

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Comparing to Other’s Data Discuss the similarities and differences between your data and another team’s data Now look at all the teams data on the bulletin board What did you notice was similar between all of the data? What does that tell us? Calculate the slope of your line and share the results? (interesting considering we all used different volumes) Any differences? What would have caused these?

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Density Definitions amount of mass in a given amount of space The ratio of the mass of an object to its volume describes how tightly packed the molecules of a substance are Density units are a unit of mass over a unit of volume g/cm 3, g/mL, kg/L, kg/m 3 Density is the universal physical property The density of water (H2O) is 1.0 g/cm 3 or 1.0 g/mL Box 1 wood cork wax float in H 2 O (water) Box 2 steel iron glass sink in H 2 O (water)

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Density Formula Density = mass volume D = m v = m m = D v v D m D v g cm 3 or mL g/cm 3 or g/mL

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Density Calculation Examples Ex 1: D = ? m = 100 g v = 50mL Ex 2 D = 10 g/mL m = ? v = 5 mL Ex 3 D = 2 g/cm 3 m = 50 g v = ? D = m v 100 g 50 mL D = 2 g/mL v = m D 50 g 2 g/cm 3 v = 25 cm 3 m = D v m = 10 g/mL 5mL m = 50 g Let’s Practice m D v

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Learning about Density Experience it Get in the Game with Density Lab Activity Finding the Density of Irregular solids with Displacement Density Columns What does density depend on? The material The temperature of the material (demos)

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Demonstration Step-by-Step Instructions 1. Record the Mass First 2. Put water in the SMALLEST CYLINDER POSSIBLE & record it enough to cover solid, not enough to overflow 3. Slide object into the cylinder & record new volume 4. Subtract the 2 volumes to find object volumes 5. Calculate Density using the formula. Find Density of Irregular Objects - Displacement Let’s Practice

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Identify the metal on the PT using Density

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Where does it go? Some important info Liq. Guess 1.______ 2.______ 3.______ 4.______ 5.______ Redwater1.0 g/mL Greenalcohol.79 g/mL Bluesoap1.03 g/mL Clearcorn srp2.2 g/mL Yellowoil.9 g/mL Density Columns ColorLiquidDensity

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Where does it go? What about these solids? Liq. Actual Density Columns 5. Syrup – 2.2 g/mL 4. Soap – 1.03 g/mL 3. Water – 1.0 g/mL 2. Oil -.9 g/mL 1. Alcohol-.79 g/mL Wood (hard).92 g/cm 3 Cork.24 g/cm 3 Rubber2.26 g/cm 3 Plastic1.03 g/cm 3 Steel8 g/cm 3 ObjectDensity

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Density Rule Less dense materials float on more dense materials Density can be affected by temperature and heat Generally the higher the temp the lower the density More on this later

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