Step 1 in the Road to Understanding Chemistry

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Measurements Ratios

• Step 1 in the Road to Understanding Chemistry

2
Identify your solid on the Periodic Table

• Compare your density to the metals on the
  Periodic Table

3
Measuring with a Metric Ruler
3.20
3.30
Length of Bar 3.2 cm estimate between marks
3.23 cm

• 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)

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Sample Measurements
Length of Bar 10.2 estimate 10.26 cm
Length of bar 11.2 cm 11.20 cm (right on line)
Lets Practice to check your skills
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Using Length to Calculate Volume

• The amount of space an object takes up
• Volume Units cm3 (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 ? ? r2 ? h
• Sphere Volume 4/3???radius3 or 4/3?circle area?r

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Practice Volume of Rectangular Prism (Box)

• 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
• V24 m3

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Practice Volume of Rectangular Prism (Box)
Note All sides must be in the same unit

• 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
• V120 000 cm3

Lets Practice
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Practice Volume of Cylindrical Prism (Box)
Note All measurements must be in the same unit

• Calculations

• Box Dimensions

• r 10 cm
• h 5 cm
• V base area height
• V ? r2 h
• V 3.14 (10 cm)2 15 cm
• V 3.14 100 15 cm2cm
• V 4710 cm3

10 cm
15 cm
Lets Practice
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Practice Volume of Sphere (Ball)
Note Moving to circles

• Calculations

• Box Dimensions

• r 5 cm
• V 4/3 ? r3
• V 4/3 3.14 (5 cm)3
• V 4/3 3.14 125 cm3
• V 523.3 cm3

5 cm
C 31.4 cm
How would you solve this if all you had was a C
31.4 cm
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Practice Volume of Sphere (Ball)
What happens if you cant measure radius?

• Calculations

• Box Dimensions

• C 31.4 cm
• First find r
• r C/2? 31.4 cm/6.28 5 cm
• Plug r into the formula
• V 4/3 3.14 (5 cm)3
• V 4/3 3.14 125 cm3
• V 523.3 cm3

5 cm
C 31.4 cm
Lets Practice
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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 dont 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
Lets Practice
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Using Liquids to Measure Volume

• 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 cant 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?

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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)
20.0 15.78
42.5 33.53
66.0 52.07
79.3 62.57
99.9 78.82
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Comparing to Others Data

• Discuss the similarities and differences between
  your data and another teams 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/cm3, g/mL, kg/L, kg/m3
• Density is the universal physical property
• The density of water (H2O) is 1.0 g/cm3 or 1.0
  g/mL

Box 1 wood cork wax float in H2O (water) Box 2 steel iron glass sink in H2O (water)
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Density Formula

• Density mass

volume
m
D
v
D m v m m D?v
D v v D m D?v
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Density Calculation Examples
m
D
v

Ex1 D ? m 100 g v 50mL Ex 2 D 10 g/mL m ? v 5 mL Ex 3 D 2 g/cm3 m 50 g v ?
m D?v
m 10 g/mL?5mL
D 2 g/mL
v 25 cm3
m 50 g
Lets Practice
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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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Find Density of Irregular Objects - Displacement

• 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.

Lets Practice
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Identify the metal on the PT using Density
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Density Columns

• Where does it go?

• Some important info

• Color Liquid Density

• Liq. Guess
• 1.______
• 2.______
• 3.______
• 4.______
• 5.______

• Red water 1.0 g/mL
• Green alcohol .79 g/mL
• Blue soap 1.03 g/mL
• Clear corn srp 2.2 g/mL
• Yellow oil .9 g/mL

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Density Columns

• Where does it go?

• What about these solids?

• Object Density

• Liq. Actual

• Steel 8 g/cm3

• Plastic 1.03 g/cm3

• Rubber 2.26 g/cm3

• Cork .24 g/cm3

• Wood (hard) .92 g/cm3

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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