Determination of the number of gas molecules


	Part II: Determination of the Number of Gas Molecules
	In part II, you will determine the number of gas molecules in the syringe for 45.0 mL samples of four different gases. The four different gases you will be measuring are nitrogen (N₂), oxygen (O₂), propane (C₃H₈), and butane (C₄H₁₀). The balloons are color coded with the type of gas, so N₂ is in a green balloon, O₂ in a blue balloon, C₃H₈ in a yellow balloon, and C₄H₁₀ in a white balloon. These gases in different colored balloons will be on the North and South sides of the laboratory at two "gas" stations.

	First, record the chemical formula of the gas you will be measuring on your data sheet in the "gas being observed" line and then make your way to a "gas" station. Draw 60.0 mL of gas into the syringe from the storage balloon with the aid of the instructor. Be sure to select the link below to watch a video of this process. (HINT: Holding the syringe tightly in your hand will heat the gas. Be careful when loading the syringe not to hold it tightly. Also, remember to carry the syringe with the tip facing up. This will prevent the "heavier-than-air" gases from flowing out of the syringe).
	Click Button Below to view this process

	The video does not show the plunger being returned to the 45.0 mL mark because this is not done until you get to a balance right before you weigh the syringe. Go to a balance and weigh the syringe with 45.0 mL of gas in it. Shown in the picture below is the mass of the syringe + 45.0 mL of the gas from the white balloon, which would be the gas butane (C₄H₁₀).

	To calculate the mass of the gas in the syringe, subtract the mass of the empty syringe from the mass of the syringe + gas (as shown below). HINT: The mass of the empty syringe was found in part I. (Mass of the Syringe and Gas) - (Mass of the Empty Syringe) = Mass of Gas 35.826 g - 35.752 g = 0.074 g
	After the mass of the gas has been recorded, then the next step is to calculate the number of gas molecules in the syringe. Since butane (C₄H₁₀) is the gas in the white balloon, we will use the molecular mass of butane. The equation below is what you use to calculate the number of molecules of butane gas in your syringe: (mass of gas / molecular mass of gas) * (6.022 X 10²³ / 1 mole of gas) = number of molecules of gas (0.074 g / 58.12 g/mol) * (6.022 X 10²³ / 1 mol) = 7.7 X 10²⁰
	(NOTE: If the first digit of your answer is 1 then three significant figures are needed, if the first digit is any other number other than 1 then two significant figures will be fine, as shown in our answer). This process will be repeated three more times, so that a measurement is made on each of the four gases. Record all of the results onto your data sheet for each gas. Here are two tips to check your results as you work: (1). The number of gas molecules is usually on the order of either x10²⁰ or x10²¹ . (2). If Avogadro's Law is true, the number of gas molecules in 45.0 mL at the same T and P should be the same for any gas sample. Thus, the number of gas molecules for each of the four gases should agree with one another. (Expect same variation in the least significant digit). If the numbers of molecules vary more than in the least significant digit, then you might want to recheck your calculations for any errors.