Sample Lab Questions Investigation #3: "Density Determinations"

Note: The subscripts and superscripts may not appear as such. It depends upon your web browser.

1.

An unknown liquid is weighed in a pycnometer 5 times.
51.1015 g, 50.0515 g, 50.0729 g, 50.0928 g, 50.1226 g

a. (3 pts) Calculate the average (to the correct number of significant figures), the standard deviation and the relative standard deviation.

b. (1 pt) The mass of the dry pycnometer = 45.0727 g. The average mass when filled with H₂O = 49.0712 g. The density of the H₂O = 0.9897 g/mL. What is the volume of this pycnometer?

c. (1 pt) Using the above data, what is the density of the unknown liquid?

2.

(2 pts) A rock, weighing 41.3 g, is placed in a graduated cylinder containing 100.0 mL of water. The volume then reads 120.3 mL. What is the density of the rock in g/cubic centimeters? (Assume 1.00 mL water = 1.00 cc).

3.

(3 pts) List 3 safety procedures you should follow with the pycnometer in Inv #3, "Densities of Liquids."

4.

(4 pts) Define and give 2 examples of each:

Intensive property -

Extensive property -

5.

(2 pts) List four measurements you need in Inv. #3 in order to calculate the density of an unknown liquid.

6.

(2 pts) Sketch a diagram of a cool Bunsen burner flame and label the area(s) and color(s) of the flame.

Answers

1. (a) average = 50.3, standard deviation = 0.455 = 0.5, RSD = 0.91 (b) 4.040 mL (c) 1.29 g/mL 2. volume of the rock is 120.3 - 100.0 = 20.3 mL, so the density of the rock is 2.03 g/cc