DENSITY OF PLASTIC SCREW ANCHORS
Problem: Determine the density of the plastic object experimentally. No
balance may be used in the procedure.
Given: Density of water is 1g/ml
Density of an isopropyl alcohol solution is 0.85 g/ml ( should use 70%
isopropyl which is what is sold at stores)
Equipment
graduated cylinders
beral-type pipets
beakers
test tubes
plastic screw anchors
Solution:
Put some alcohol in a cylinder. When the plastic piece is dropped into the
alcohol, it will sink. This tells you that the density of the plastic is greater than the
alcohol. Put some water in a cylinder and use a beral-type pipet to drip water
into the alcohol. Continue to drip the water in to the alcohol until the plastic piece
floats in the middle of the liquid. At this point, the density of the solution is the
density of the plastic.
To determine the density of the liquid, calculate the total mass of the solution by
using the volume of the water and alcohol and determining the mass from the
density. Get the volume of the solution by reading off the cylinder after removing
the plastic piece.
NOTE: You may not add the two volumes together to get the final volume.
Because of intermolecular attractions, the volumes are not additive.
mass of water = density of water x vol of water used
mass of alcohol = density of alcohol x vol of alcohol used
mass of mixture = mass of water + mass of alcohol
vol of mixture = what’s read on cyl after removal of plastic piece
then calculate density of mixture which = density of plastic piece