8th Grade Science – Professor Shai

Density of Liquids Experiment

Section 3.9 – Page 51

You are going to measure the density of an odorless, colorless liquid.  Half the class will have one liquid called Mystery A, and the other will have Mystery B.  Don’t taste the liquid, yuck!

To measure the density of a liquid you do the same thing you would for a solid.  Mass the fluid, find its volume, and divide mass by volume.

To mass the fluid, weigh it in a container, pour it out, weigh the empty container, and subtract the mass of the empty container from the full container.

To find the volume of the fluid, you simply measure it very carefully in a graduated cylinder.

Question:  Should you first find the volume of the liquid or mass the liquid?

1.  Weigh fluid in beaker.  Pour out to graduated cylinder, and weigh again.  The mass of the fluid is the difference of the two weighings.  The volume is the measurement you see in the graduated cylinder.  Note that this method does not include the remants of fluid that cling to the beaker in the massing.  The remants are also not oncluded in the volume measurement.

2.  Pour the fluid into a graduated cylinder and read its volume.  Then weigh the graduted cylinder.  Then pour the fluid out, and weigh again.  The weight of the fluid is the difference between the two weighings.  Note that this method, after pouring the fluid from the graduated cylinder, includes the remnants of fluid in the volume reading, but not in the mass calculation.

And the right way to do it is (1).  When you find the mass or measure the volume of the fluid, you will not include the fluid that clings to the empty container from which you poured it. Therefore, you should mass first as in choice one above. In choice 1, after you mass and then pour to measure volume, the remnants of fluid left in the beaker do not get included in the mass or the volume calculation.   Getting included in neither is fair.  However, if you find the volume first, and then mass, the remnants of fluid in the graduated cylinder volume would be included in the volume measurement but not in the mass measurement.

Report the density of your liquid on the board.

Are the two liquids the same?

When you mix salt with water, the total volume decreases but the mass remains the same.  What should happen to the density?

8th Grade Science – Professor Shai

Density of Liquids Work Sheet

Fluid 1 Density Analysis

# Mass of Beaker After Pouring Fluid            B. _________

## Volume of Actual Fluid                               D. _________

Density of Actual Fluid (C / D)                   E. _________

Fluid 2 Density Analysis

# Mass of Beaker After Pouring Fluid            B. _________

## Volume of Actual Fluid                               D. _________

Density of Actual Fluid (C / D)                   E. _________

Report your group result on the histogram on the board.

Do problem 15 in your text.