1. Density of Liquids and Solids
Experiment 2

2. What is the Density? Density is how compact a substance is
He atoms have a mass of 4 amu and are about 3 nm apart
Density is how compact a substance is
How close are all the atoms to each other and how heavy are those atoms?
We define the density, d, to be 𝒅= 𝒎𝒂𝒔𝒔 𝒗𝒐𝒍𝒖𝒎𝒆
For He 𝑑 𝐻𝑒 = 4 𝑔𝑟𝑎𝑚 22.4 𝐿 = 𝑔 𝑚𝐿
For Au 𝑑 𝐻𝑒 =19.3 𝑔 𝑚𝐿
Gold is 0.5 million times more dense!
Au atoms have a mass of nearly 197 amu and are about 0.4 nm apart

3. Relative Density
In liquids and gases the densest material falls to the bottom and the least dense materials float to the top because the force of gravity is stronger on more dense objects
Least dense
S1 – Cork
Mineral Oil – L1
S2 – Ice
S3 – Rubber Stopper
Corn Syrup – L2
S4 – Marble (Glass)
Most dense
Glass >
Corn Syrup >
Rubber >
Water>
Ice>
Mineral Oil>
Cork

4. Measuring the Density
To measure the density we need to measure the mass, m and the volume V
Then we divide the mass, m, by the volume, V, to get the density d
𝒅= 𝒎𝒂𝒔𝒔 𝒗𝒐𝒍𝒖𝒎𝒆 = 𝒎 𝑽

5. Density: Getting the Mass m
When dealing with liquids and gases, we measure the mass of our unknown, munk, indirectly by a technique called weighing by difference.
First weigh empty flask or beaker to get m1
Then weigh the same flask with some amount of your unknown in it to get m2
The mass of your unknown munk = m2 – m1 = g g
munk = g
m1 = g
m2 = g

6. Density: Getting the Volume: Solids
Then to get the density we need to measure the volume the way this is measured is different depending on if we have a solid or a liquid
We can get the volume Vunk of an insoluble, irregularly-shaped, solid using volume by displacement
Vunk = V2 – V1 = 266 mL – 195 mL = 71mL
V2 = 266 mL
V1 = 195 mL

7. Density: Getting the Volume: Liquid
Best to use a pipette
Or burette

8. Volume of Rectangular Solid
Measure, length L, width W, and height H

9. Calculating the Density
Density of a Liquid
10.00mL of a liquid pipetted into a flask, the mass of the liquid (weighing by difference) g
𝑑= 𝑚 𝑉 = 𝑔 𝑚𝐿 = 𝑔 𝑚𝐿 =1.014 𝑔 𝑚𝐿
Density of a Rubber Stopper
Stopper mass = 8.453g, displaces 6.5mL of water in a graduated cylinder
4 sig. figs
2 sig. figs

10. Thickness of Aluminum Foil
Aluminum foil is too thin to measure its thickness, H, with a ruler
Instead we measure the thickness by using the density of aluminum to help us
Measure the dimensions of a rectangular piece of foil
W = cm
L = cm
Measure the mass of the foil = M
M = g
Knowing the density of Aluminum = 2.70 g/cm3
2.70 𝑔 𝑐𝑚 3 = 𝑀 𝑉 = 𝑀 𝐿×𝑊×𝑯
𝑯= 𝑔 10.10𝑐𝑚×10.75𝑐𝑚×2.70 𝑔 𝑐𝑚 3
𝑯= 𝑀 𝐿×𝑊×2.70 𝑔 𝑐𝑚 3
𝑯= 𝑐𝑚=1.54× 10 −3 𝑐𝑚

11. Objectives
To observe the relative densities of some common liquids and solids
To determine the densities of water, an unknown liquid and an unknown rectangular solid
To determine the thickness of a piece of aluminum foil using the density concept
To gain proficiency in pipetting, weighing by difference and determining a volume by displacement

12. Tonight
Measure density of water with 10mL pipette and 125 mL Erlenmeyer Flask (2 Trials)
Measure density of an unknown liquid with 10mL pipette and 125 mL Erlenmeyer Flask (2 Trials)
Density of a #2 Rubber Stopper – (water displacement with 100mL Cylinder – 2 Trials)
Density of rectangular solid – block of wood
Thickness of a piece of rectangular Aluminum foil by measuring its mass and assuming it has a density of 2.70 g/cm3