Mrs. Howland Chemistry 10 rev. 2015

Which has greater mass? 100 kg of lead or 100 kg of feathers?

Although 100 kg of feathers may take up much more room than 100 kg of lead, they both still weigh 100 kg! The steel has greater mass for its size because it is more DENSE Thus, a material such as feathers takes up much more room (volume) than a denser material such as steel, for the same mass or weight

Density is the Mass per unit Volume If you take the same volume of different substances, then they will have different MASSES Q) Which has the greatest mass and therefore the most dense? What IS density?

Density is a PHYSICAL PROPERTY Density ~ mass per given volume of a material Steel has a greater density ~ 7.8 grams of mass per cubic centimeter Aluminum has a lower density ~ 2.7 grams/ cm 3 It’s not just about solids! Liquids & gases are matter & have density, too

In order to understand DENSITY, we need to understand a few key terms! MASS ~ The measure of how much matter is in a particle or object VOLUME ~ The amount of space that an object or substance occupies PHYSICAL PROPERTY ~ Characterization of matter, not relating to a chemical change EXTENSIVE PROPERTY ~ changes when the size of the sample changes (EX: mass, volume) INTENSIVE PROPERTY ~ depend on the amount of matter being measured (EX: density, hardness)

DENSITY IS AN INTENSIVE PROPERTY EXAMPLE: A steel nail and a steel cube have different masses, so they have different amounts of matter Their VOLUMES are also different! BUT if you calculate density (density = mass ÷ volume) the DENSITY is the same for both the nail and the cube, despite “how much” you have!

Which one is MORE dense? If each box has the same volume, and each ball has the same mass, which box would weigh more? Why?

Solids that are strong, such as steel, typically have high density. HIGH density means there are many atoms per cubic centimeter (EXAMPLES: mercury, lead) Soft materials typically have lower density Solids with low density are not as strong LOW density means there are relatively large spaces between atoms – this is why ICE is more dense than liquid water! (EXAMPLES: gasoline, cork)

Density is an “ID Tag” for common substances

The density of a material depends on two things: 1.The individual mass of each atom or molecule 2.How tightly the atoms are packed

To calculate density, you need to know the MASS and the VOLUME

We will measure mass using a digital balance

Use a metric ruler Measure all 3 sides: length, width, height  UNITS: mm, cm, m, km (base unit is meters!) Volume = L x W x h

Use a metric ruler Measure the height & diameter Divide the diameter in half to find the radius  UNITS: mm, cm, m, km (base unit is meters!)

Water Displacement method Fill a graduated cylinder with water  Read initial volume Drop the object in (without splashing water!)  Calculate the change in volume! UNITS: mL, L

Find the density of a cube measuring 5.7cm on a side, with a mass of 630 g.

Cover up what you are solving for! Divide up and down and multiply across. Here we are solving for VOLUME. VOLUME = Mass / Density

A student determines the density of manganese to be 5.54 g/cm 3. If a sample had a mass of 3.43g what was the volume? The density of benzene is 0.88 g/mL. Calculate the mass of 250 mL of benzene.

Volume is derived from length This cube has volume of 1 m 3 There are 10 decimeters in a meter, so the volume is : (10 dm) 3 = 1000 dm 3 A cubic decimeter (1 dm 3 ) is also called a liter (L) 1 decimeter = 10 cm, so 1 liter can be divided into 1000 cubes that each have a volume of 1 cm 3 THUS: 1 cm 3 = 1 milliliter (mL)