Density

Today we will be focus on how mass and volume can be related. There are 2 things that make something matter. It has mass This means that it is made of particles. It has volume This means that it takes up space. Today we will be focus on how mass and volume can be related.

In the lab, mass is measured in ______.or __________. grams kilograms Mass is measured using either a __________ or a __________. scale balance

In the lab, volume is measured in _________ or __________. liters milliliters Volume is measured using a __________________. graduated cylinder

This means that a milliliter is equal to a cubic centimeter Remember: In science, we always use the International System of Units (SI units), also known as the metric system. Milliliters are defined as the amount of space in a cube whose sides are all 1 cm in length. 1 cm 1 cm 1 cm This means that a milliliter is equal to a cubic centimeter 1 mL = 1 cm3 We will often use mL to describe the volumes of liquids and cm3 to describe the volumes of solids, but they are just 2 ways of saying the same thing!

Density is the relationship between mass and volume Density is the relationship between mass and volume. It is the measurement of how tightly the particles of a substance are packed together. Which sample is the most densely packed? Sample 1: Solid Iron Sample 2: Liquid Iron Sample 3: Iron Vapor

Density and the Phases of Matter Solid Iron Liquid Iron Iron Vapor Notice that solids are the most dense phase of matter and gases are the least dense phase of matter.

Density shows the relationship between mass and volume Density shows the relationship between mass and volume. The formula on your formula chart represent this relationship mathematically. m D v Use the formula to derive all three ways of expressing this relationship. m v m D D = m = D × v v =

milliliters or cubic centimeters Since density is the relationship between mass and volume, we must show this relationship in the units of density. m v What are the units of mass? D = grams What are the units of volume? milliliters or cubic centimeters mL v g m cm3 v g Units of D = or

word problems on your notes. Complete the density word problems on your notes.

68.4 86.8 Before After The picture shows a graduated cylinder on a scale before and after a solid sample was placed into it. Use the information in the picture to determine the density of the solid. 13 mL 18.4 g v m Mass = 86.8 g - 68.4 g = 18.4 g D = = 1.4 g/mL Volume = 36 mL - 23 mL = 13 mL

Diffence means subtract! 68.4 86.8 Before After When shown the mass and volume before and after a sample has been added, you find the difference in the masses and the difference in volumes first. Then you have the information you need to calculate the density. Diffence means subtract! 13 mL 18.4 g Mass = 86.8 g - 68.4 g = 18.4 g D = = 1.4 g/mL Volume = 36 mL - 23 mL = 13 mL

They are all equally packed together: they all have the same density! Visualizing Density: Which of the samples below is the most tightly packed together and therefore, the most dense? A B C They are all equally packed together: they all have the same density!

Remember: Density is the relationship between mass and volume. It is a physical property of matter. At a given temperature, different samples of the same substance will have the same densities regardless of the amount of the substance in each sample. 3 samples of the same substance are shown below along with their individual masses and volumes. Calculate the density of each. Mass = 17.50 g Volume = 13.0 cm3 Mass = 8.75 g Volume = 6.50 cm3 Mass = 35.0 g Volume = 26.0 cm3 Density = 1.35 g/cm3 Density = 1.35 g/cm3 Density = 1.35 g/cm3

3 samples of the water are shown below along with their individual masses and volumes. Calculate the density of each. Mass = 85.0 g Volume = 85 cm3 Mass = 40.0 g Volume = 40 cm3 Mass = 60.0 g Volume = 60 cm3 Density = 1.0 g/cm3 Density = 1.0 g/cm3 Density = 1.0 g/cm3

So why does temperature matter? Remember: Density is an intrinsic physical property of a substance. It does not matter how much of the substance is in a sample. If they are all the same temperature, then they will all have the same density! So why does temperature matter? As the temperature of matter increases, its particles expand! This makes the matter LESS dense!

We will discuss temperature more next class We will discuss temperature more next class. Now we will learn how matter with different densities interact. Based on your observations, how do liquids with different densities stack? The liquid with the greatest density will be on the bottom!

A B C If these 3 liquids are placed into the same beaker, how will they stack? (Assume that they will not mix when stacked in the correct order.) A B C Density of liquid 1.21 g/mL Density of liquid 5.82 g/mL Density of liquid 3.07 g/mL Sample A Sample C Sample B

Watch what happens when each solid is placed into water. Q: What is the density of water? A: 1.00 g/mL Watch what happens when each solid is placed into water. D = 1.25 g/cm3 c D = 0.50 g/cm3 D = 2.85 g/cm3 D = 0.95 g/cm3 Density of water 1.00 g/mL Density of water 1.00 g/mL Density of water 1.00 g/mL Density of water 1.00 g/mL Explain what determines if a solid floats or sinks: If the solid is more dense than the liquid, it sinks. If the solid is less dense than the liquid, it floats.

The density of the cube is 0. 85 g/cm3 The density of the cube is 0.85 g/cm3. Based on what you have just learned, when will this cube stop sinking if it is placed into the cylinder shown? It sinks through the ether because it is more dense than ether, but it floats on the water because it is less dense than water.

Important Vocabulary: What force causes things to float? The Buoyant Force Fluids exert a buoyant force on objects that are placed inside of them. Fluids with greater densities exert a greater amount of buoyant force. This is why objects might sink through one layer, but float on the next. Buoyancy makes things float!

Dissolved solutes make aqueous solutions more dense! When solutes dissolve in water, they also affect the density of the water. Do dissolved solutes make an aqueous solution more dense or less dense? Dissolved solutes make aqueous solutions more dense! This is why the salt water in the ocean is more dense and easier to float on than freshwater. 22

What force affects how fluids pour? Viscosity affects how things pour! Important Vocabulary What force affects how fluids pour? Viscosity Viscosity is like the friction in a fluid. It affects how fast a fluid is able to flow or pour. High Viscosity Low Viscosity Viscosity affects how things pour! 23