7 th Grade: November 4th Trim and Glue in Journal: “Cornell: Practice Problems” Hint: You can...
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Transcript of 7 th Grade: November 4th Trim and Glue in Journal: “Cornell: Practice Problems” Hint: You can...
7th Grade: November 4thTrim and Glue in Journal:
“Cornell: Practice Problems”
Hint: You can cut BOTH at the same time!
REMINDER:
Quiz is Monday
Homework due Monday
Density is defined as mass per unit volume. It is a measure of how tightly packed and how heavy the molecules are in an object. Density is the amount of matter within a certain volume.
What is density?
Density is a comparison of how much matter there is in a certain amount of space.
Each element on the periodic table has a specific density.
The density of an element is the same no matter what the size or mass of the sample.
Density can be used to identify elements
Density is a physical property of a substance that is used to identify that substance.
The size of the object does not change the density. The density of lead is always going to be the same.
DensitDensity of y of LeadLead
DensitDensity of y of LeadLead
Density Density of Leadof Lead
MassMeasurement of the amount of matter
(or stuff) in an objectMeasured in grams (g)
There are 3 states of matter:
Solid
Liquid
Gas
There are 3 states of matter:
Solid
Liquid
Gas
Volume
Measurement of the amount of space an object takes upMeasured in milliliters (ml) or cm3
Finding Volume
To find the volume of a liquid, use a graduated cylinder
Make sure to read the bottom of the meniscus
• Identifying your units!
The base unit for mass (m) of an object is grams (g).
The base unit for volume of a solid is cubic centimeters (cm3).
The base unit for volume of a liquid is milliliters (ml)
Which one is more dense?
Demonstration: People in a square
How about this: Which square is more dense?
Which one is more dense?
Now which one is more dense?
What is density?
Density = mass OR mass ÷ volume.
volume
Units for density: g/cm3
g/mL
Why are these the units for density?
ALWAYS REMEMBER
UNITS!
The Triangle forVolume, Mass, and Density
M ÷ ÷D X V
Density = MV
Volume = MD
Mass = D x V
1) Find the mass of the object
2) Find the volume of the object
3) Divide : Density = Mass - Volume
To find density:
Ex. If the mass of an object is 35 grams and it takes up 7 cm3 of space, calculate the density.
1) Find the mass of the object
2) Find the volume of the object
3) Divide : Density = Mass - Volume
To find density:
Set up your density problems like this:
Given: Mass = 35 grams Unknown: Density (g/ cm3) Volume = 7 cm3
Formula: D = M / V Solution: D = 35g/7 cm3
D = 5 g/cm3
Ex. If the mass of an object is 35 grams and it takes up 7 cm3 of space, calculate the density.
Solving for Density
Jack has a rock. The rock has a mass of 6g and a volume of 3cm3. What is the density of the rock?
Jill has a gel pen. The gel pen has a mass of 8g and a volume of 2cm3. What is the density of the rock?
Solving for Mass and Volume
Calculate the mass of a liquid with a density of 3.2g/mL and a volume of 25mL.
*Find the volume that 35.2g of carton tetrachloride (CCl4) will occupy if it has a density of 1.60g/mL.
A 2.75 g sample of a substance occupies a volume of 250.0cm3. Find its density.
The density of ethanol is 0.780g/mL. Find the mass of a sample of ethanol that has a volume of 150.0mL.
A rectangular block of lead measures
2cm x 3cm x 4.5cm. If the density is 11.34g/cm3, calculate the mass of the block.
Jake has a book, a ruler, and a balance. How can Jake find the density of the
book with the tools he has?
Measure Book : Length, Width, HeightCalculate Volume: LxWxHMeasure mass with TBBPlug into Density Formula
Finding Volume
Water Displacement Method- Read the initial volume of water in a graduated cylinder- Place object into cylinder- Read the final volume of water- Final – Initial = Volume of the object
Reading a Graduated Cylinder
Meniscus
Initial Height of Water
350 mL
1st Water Level
With an Irregular Shaped Object
Initial Height of Water
350 mL350 mL
Place object into water and read level again.
1st Water Level 2nd Water Level
With an Irregular Shaped Object
Initial Height of Water
350 mL
425 mL
Place object into water and read level again.
1st Water Level 2nd Water Level
With an Irregular Shaped Object
Initial Height of Water
350 mL
425 mL
Place object into water and read level again.
1st Water Level 2nd Water Level
With an Irregular Shaped Object
Subtraction Problem
2nd water level
- 1st water level
425 mL
- 350 mL
75 mL
DENSITY OF AN IRREGULAR SOLID
Find the Mass of the solid Find the Mass of the solid on a balance.on a balance.Fill the Measuring Cylinder Fill the Measuring Cylinder with Water to a known with Water to a known Volume.Volume. Add the Object.Add the Object. Work out the Volume of Work out the Volume of Water that is displaced.Water that is displaced. Calculate the Density.Calculate the Density.
50 cm3
80 cm3
m = 360 g = m = 360 =12.0 g/cm3
V 30
Water Displacement Practice
An irregular object with a mass of 18kg displaces 2.5 L of water. Calculate the density of the object.
An irregularly-shaped sample of Aluminum has a mass of 43.6g. The student uses water displacement to find the volume. The initial volume reading is 25.5mL, and after the Al is added, the water has risen to 41.7mL. Find the density of the Al.
One more Example….
A cube of gold (Au) has a side length of 1.55cm. If the sample is found to have a mass of 71.9g, find the density of Au.
Liquid Layers
If you pour together liquids that don’t mix and have different densities, they will form liquid layers.
The liquid with the highest density will be on the bottom.
The liquid with the lowest density will be on the top.
Liquid Layers
Which layer has the highest density?
Which layer has the lowest density?
Imagine that the liquids have the following densities: 10g/cm3. 3g/cm3.6g/cm3. 5g/cm3.
Which number would go with which layer?
Liquid Layers – Try with your neighbor
Which liquid has the highest density?
Which liquid has the lowest density?
Which liquid has the middle density?
Liquid Layers – Try on your own!
Imagine that the liquids on the right have the following densities:15g/cm3 10g/cm3
3g/cm3 9g/cm3
7g/cm3 12g/cm3
Match the colors to the correct densities.
3g/cm3
7g/cm3
9g/cm3
10g/cm3
12g/cm3
15g/cm3
Review
What is the formula for density?What happens if you pour together liquids
that have different densities?Will the liquid on the top have the highest
or lowest density?Will the liquid on the bottom have the
highest or lowest density?
Supplies: Each person needs 1 cranberry, 1 Powerade, 1 diet 7 up, and 1 clear plastic cup of ice.
Prediction: Which substance is most dense? Which substance is least dense?
Task: Poured Cranberry juice in first over a piece of ice; Gatorade in slowly over a piece of ice; and then diet 7 up slowly over a piece of ice. Observe what happens.
Conclusion: Why was cranberry juice the most dense?
Reason Why: They stayed in separate layers based on sugar content.
ApplicationWhat’s Happening: think about ocean and continental crusts, apply what happened with the drink to what you know about these two crusts…
Ocean floor crust is heavier and more dense than continental crust (because of the water
Density Homework – due Thursday