Density = Mass/Volume

Determining Density

• First, you’ll need to find the mass (given in grams).

• Do this by weighing the specimen.

• A Triple Beam Balance will be used.

Triple Beam Balance

• has a pan to put the specimen on;

• three sliding weights that slide along three scales (beams); and

• a pointer that points to zero when everything balances!

Starting Off1. the pan should be empty, 2. the weights should all be to the left at zero, 3. make sure the pointer points to zero! 4. then you put the specimen on the pan!"

Now Slide the Weights• Slide the weights until they counterbalance the specimen! • The top two scales are notched and the weights must each rest in a notch! • The top scale is in tens of grams: 0, 10, 20, etc. • The middle scale is in hundreds: 0, 100, 200, etc. • The bottom scale has no notches. • The weight can rest anywhere along the scale! • The scale is in units: 0, 1, 2, 3, etc. It also shows tenths of units! • For this specimen, the hundreds scale is at 100, the tens scale is at 50, and the

units scale is at 5.8. So the weight of the specimen is 155.8 grams!"

Finding VolumeTwo Ways to Find Volume:1. Using a ruler for a regularly shaped object.

• Volume = Length (cm) X Width (cm) X Height (cm)• Final answer is in cm3 (centimeters cubed)

2. An irregularly shaped object uses displacement:

• using a graduated cylinder and immersing the specimen in the partly filled cylinder and seeing how much the water level rises

• Final answer is in milliliters (mL)

Displacement Example• Read the starting level of the water! The cylinder has a scale with marked

divisions every ten ml (milliliters) and labeled divisions every hundred ml • Next, you immerse the specimen completely in the water! • The water level rises to 920 ml!“• So the volume of the specimen equals the difference between the starting

level of the water (900 ml) and the final level of the water (920 ml)! • That's 20 ml• A cubic centimeter and a milliliter have the same volume!

Density Lab

• Click picture to complete density lab.

Properties of Water• 1 square box, 1 cm long on each

side has a volume of 1 cm3

• Fill the box with H2O and it contains 1 cm3 of H2O

• Pour the water into a graduated cylinder you have a liquid volume of 1 mL

• If you measure its mass on a balance, it will be 1 g

• Therefore, the density of water = 1 g/cm3 or 1 g/mL

• Because of this property you can use water to measure irregularly shaped objects in a cylinder using the displacement method

Sink or Float?

Remember Density of Water is 1 g/cm3 or 1 g/mL

• Sink:– Density > 1 g/cm3

• Float:– Density < 1 g/cm3

Width = 1 cm

Height = 1 cm

Length = 1 cm

Volume = Length X Width X Height1 cm X 1 cm X 1cm = 1 cm3

References

• http://academic.brooklyn.cuny.edu/geology/leveson/core/graphics/density/density_def.html

• http://academic.brooklyn.cuny.edu/geology/leveson/core/linksa/mineral_invest_intro.html