Lab 2. Density

Introduction to Density

The density of a substance is the amount of mass per unit volume. The density is a physical property of a substance, and it does not depend on the amount material.

We can calculate the density of a substance if we know how much mass correspond to a given volume. It is usually expressed in grams per milliliter (g/mL) or gram per cubic centimeter (g/cm3). For example, for “substance A”:

Density and Floating

The density of a substance determines whether it will float or sink in another substance.

· A substance will float if it is less dense than the liquid it is placed in.

· An object will sink if it is denser than the liquid it is placed in

Determination of the density of liquids

In this laboratory, we will determine the density of liquids by:

· Obtaining the mass by difference method (subtracting the mass of the empty beaker)

· Obtaining the volume by reading the graduated cylinder. Pay close attention, given the graduated cylinder in this experiment, your volume reading should not contain any decimals

Determination of the density of solid by displacement of liquids

In this laboratory, we will determine the density of solid by:

· Obtaining the mass by directly weighing on the balance.

· Obtaining the volume by difference method (Vfinal– Vinitial)

Important considerations

· When measuring the density of solids: determine the mass first, then the volume.

· Pay close attention to significant figures.

Part 1. Density of an unknown liquid

1. Volume of liquid: ____30.0 mL

2. Mass of beaker: ____127.95 g

3. Mass of beaker + liquid: ____156.85 g

4. Mass of liquid: _______________

5. Density of liquid (show work): _______________

Part 2. Density of a Solid by displacement of water

6. Mass of solid: _______8.40 g

7. Volume of water: _______35.0 mL

8. Volume of water + solid: _______42.0 mL

9. Volume of solid: _______________

10. Density of solid (show work): _______________

Will the solid sink or float if dropped in unknown liquid? explain______

Part 3. Miscibility of liquids (try at home):

Miscible liquids completely combine to form one solution.

Immiscible liquids do not mix completely (heterogeneous mixture)

Fill a small container with half water and a few tablespoon of cooking oil

11. Are water and oil miscible or immiscible? __________________________________

12. Which liquid is at the top? Which liquid is at the bottom? _____________________________

13. Explain this in terms of density. ___________________________________________ Is it going to be different if you add this liquids in reverse order?______________

Part 4. Density of a metal by displacement of water

Density

14. Watch the YouTube video and fill out the table based on measured numbers observed in the experimental demonstration. Make sure to use correct significant numbers (may not be the case in this video).

Metal sample

Mass of metal (g)

Volume of water (mL)

Volume of water + metal (mL)

Volume of metal (mL)

Density

1

2

3

4

Plot volume of metal (x-axis) against mass of metal (y-axis) to obtain a best fit straight line, the slope of which should be the density of the metal. This value should be close to average value.

Part 5. Additional problems

15. A ball of material “X” has a mass of 10.830 g and occupies a volume of 19 mL.

What is the density of material “X”? _______________

16. What will happen to a ball of material “X” if placed in a container with gasoline?

Will the ball of material “X” float or sink? Explain in terms of density. ______________________________________________________________________________________________________________________________________________________