Question

 

1. Finding the volume of a flask. A student obtained a clean dry glass-stoppered flask. She weighed the flask and stopper on an analytical balance and found the total mass to be 31.601 g. She then filled the flask with water and obtained a mass for the full stoppered flask of 60.735 g. From these data, and the fact that at the temperature of the used water its density is 0.9973 g/cm3, find the volume of the stoppered flask.

a. First we need to obtain the mass of the water in the flask. This is found by recognizing that the mass of a sample is equal to the sum of the masses of its parts. For the filled stoppered flask:

(Mass of filled stoppered flask) = (mass of empty stoppered flask) + (mass of water), so (mass of water) = (mass of filled flask) – (mass of empty flask).

Calculate the mass of water.

Mass of water = ___________________ g - _______________ g = _________________ g

b. The density of a pure substance is equal to its mass divided by its volume: density = (mass/volume) or volume = (mass/density).

The volume of the flask is equal to the volume of the water it contains. Since we know the mass and density of the water, we can find its volume and that of the flask. Calculate the volume of the flask.

(Volume of water) = (volume of flask) = ________________ cm3

2. Finding the density of an unknown liquid. Having obtained the volume of the flask, the student emptied the flask, dried it, and filled it with an unknown whose density she wished to determine. The mass of the stoppered flask when completely filled with liquid was 56.796 g. Find the density of the liquid.

a. First we need to find the mass of the liquid by measuring by difference:

(Mass of liquid) = __________________ g - _______________________ g = ____________________ g

b. Since the volume of the liquid equals that of the flask, we know both the mass and volume of the liquid and can easily find its density using the equation in 1b. Make the calculation.

(Density of liquid) = _________________ g/cm3

3. Finding the density of a solid. The student then emptied the flask and dried it once again. To the empty flask she added pieces of metal until the flask was about half full. She weighed the stoppered flask and its metal contents and found that the mass was 99.323 g. She then filled the flask with water, stoppered it, and obtained a total mass of 120.827 g for the flask, stopper, metal, and water. Find the density of the metal.

a. To find the density of the metal we need to know its mass and volume. We can easily obtain is mass by the method of differences:

(Mass of metal) = ________________ g - _____________________ g = ___________________ g

b. To determine the volume of metal, we note that the volume of the flask must equal the volume of the metal plus the volume of water in the filled flask containing both metal and water. If we can find the volume of water, we can obtain the volume of metal by the method of differences. To obtain the volume of the water we first calculate its mass:

Mass of water = mass of (flask + stopper + metal + water) – mass of (flask + stopper + metal)

Mass of water = ______________ g - ____________________ g = __________________ g

The volume of water is found from its density, as in 1b. Make the calculation.

Volume of water = _____________________ cm3
c. From the volume of the water we calculate the volume of metal:

cm3

Volume of metal = volume of flask – volume of water
Volume of metal = _________________ cm3 - __________________ cm3 = __________________

From the mass and volume of the metal we find the density, using the equation in 1b. Make the calculation.

Density of metal = _____________________ g/cm3

Answer 1