Density

A Characteristic Property of Matter

Density

• Density is a basic characteristic property of all matter

• A characteristic property is a property that stays the same for a particular type of matter. For instance: H2O boils at 100 oC and freezes at 0 oC

• Every substance has a density that can be measured

• Scientists use density to help identify different kinds of matter

Formula for calculating density

•Density is mass per unit of volume

•Density is mass divided by volume

D =

Unit for Density

• Mass is measured in

grams• Volume is measured in

ml or cm3

• Therefore, the unit for density is

g/ml or g/cm3

How Do We Measure mass?How Do We Measure mass?

• Scientists use a triple beam balance to measure mass.

• What is the mass illustrated on the triple beam balance?

How do we measure How do we measure volume?volume?

• How would you use to measure the volume of a regularly shaped object, such as a box?

Which one is the meter

stick?

• V = l x w x h• How would you use to measure the volume an

irregularly shaped object, such as a rock?

You Have Choices!You Have Choices!

• Both choices involve water

• Both choices move water out of the way to make room for the object

• To move something out of the way to make room for something else is called DISPLACEMENT

• Therefore, this method is referred to as the

WATER DISPLACEMENT METHOD

But First, let’s review how But First, let’s review how to read the volume of a to read the volume of a

fluidfluid• Does the word meniscus ring a bell?• Meniscus: the curvature of a liquid in a

tube• Most liquids curve down, some curve up• If the liquid curves down, you measure the

bottom of the curve• If the liquid curves up, you measure the top

of the curve• What is the volume of the H2O and the Hg

(mercury)?

The Proper Way to MeasureThe Proper Way to Measure

• Eye Level!

OK, back to the choices!OK, back to the choices!

• Method #1: Place object in graduated cylinder and read the increase in volume.

• Method #2: Place the object in an overflow can and measure the amount of water displaced.

QuestionQuestion

• How would you measure the MASS of a liquid?

• What must you remember to do first?

Now you can calculate Now you can calculate densitydensity

• You can measure the mass of the object

• You can measure the volume of the object

• Divide the mass of the object by it’s volume and

you have calculated the

density

Minds on ScienceMinds on Science

• Obtain 2 different size graduated cylinders

• Fill each cylinder about half full with H2O

• Determine mass and volume of the H2O in each cylinder

• Calculate the density of the water in cylinder #1

• Calculate the density of the water in cylinder #2

• What did you find out?

densitydensity

• Density of a substance is a characteristic property

• This means that density will always be same for that substance no matter the size or amount.

• Example: The density of H2O is always 1g/ml or 1g/cm3

Minds on!Minds on!

• Explain this, if you can• Hint, density is involved and

something else that can affect the density of a liquid.

THINK