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In this exercise you will find the mass of several gases (as a class) and prepare a Relative atomic mass table from your data.
Procedure:
1) Read the procedure given below and prepare an appropriate data table before beginning
2) Obtain a dry round bottomed flask + stopper assembly. Obtain the mass of this equipment.
3) Pump out the air from the assembly, seal it, and obtain its mass
4) With the help of your teacher, fill the flask with the gas you have been assigned (W, X, Y, OR Z), sealing the flask after the gas has equalized pressure with the atmosphere.
5) Weigh the flask and Gas.
6) Release the gas, and pump out the assembly once again sealing it.
7) Invert the flask into water and open the seal, the flask will fill with water.
8) Pour the water into a graduated cylinder and record the volume of water you had. This represents the volume of the gas.
Calculations and questions: ( Answer these in your lab book )
1) Find the mass of each of the four gases from the class data
2) Calculate the density of each gas in g/dm3.
3) Assuming you had obtained exactly 1 dm3 of each gas from this technique, explain how the number of molecules of Gas W in the 1 dm3 flask relates to the number of molecules of Gas X in the 1 dm3 flask?
4) How does the number of molecules of Gas Y in the 1 dm3 flask relates to the number of molecules of Gas Z in the 1 dm3 flask?
5) How does the number of molecules of Gas W in the 1 dm3 flask relates to the number of molecules of Gas Z in the 1 dm3 flask?
6) With this information we can make a scale of Relative Molecular Masses (RMM). Arbitrarily assign your lightest gas a RMM of 1. By dividing the mass of each gas by the mass of the lightest one we can make a RMM scale.
Example:
Gas A has a density of 1.5g/ dm3 and Gas B has a density of 4.0 g/ dm3.
Gas A is lighter, therefore 1.5/1.5 = 1 and A has a RMM of 1.
Gas B is 4.0/1.5 = 2.67. Therefore Gas B has a RMM of 2.67.
This means one molecule of Gas B is 2.67 times heavier than 1 molecule of Gas A.
Make a scale of RMM for Gases W, X, Y, Z
7) Use your table of RMM to answer the following:
(i) In a 1 dm3 sample of each gas (W,X,Y, and Z), at the same temperature and pressure, which gas
a) weighs the most?
b) Weighs the least?
c) Has the most number of molecules?
(ii) In a 10 g sample of each gas (W, X, Y, and Z) which gas
a) Has the most molecules?
b) Has the fewest molecules?
c) Would occupy the largest volume if the temperature and pressure were the same?
d) Would have the highest kinetic energy if the temperature and pressure were the same?
9) Use a periodic table to answer the following:
i) How much heavier is one atom of carbon than 1 atom hydrogen?
ii) How much heavier is one atom of oxygen than 1 atom of carbon?
iii) How much heavier is one atom of copper than 1 atom of oxygen?
iv) If a certain sample has 20g of copper, what mass of oxygen would be needed in order to have the same number of atoms of oxygen as there are atoms in the 20g sample of copper?
v) Which contains more atoms: 4 g of Helium or 10 g of Carbon?
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