Chem Class- November 3

Today we marked a few questions from our previous assignment. Here's an example of one:

Find the mass in grams of 1 million CO molecules: 1 million Co molecules x 1 mol/6.02 x 10 to the power of 23 molecules x 28 g /1 mol = 4.65 x 10 the power of -17.

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We also did the Molar Volume Lab. We explained a bit about how it would work in the last entry, but here it is anyway.

Problem: To experimentally determine the molar volume of a gas.


Materials: Butane, sink, water, 100 mL Graduated Cylinder, Weight scale

Hypothesis: What is the expected value for the molar volume of Butane at STP?

Prelab:
1) The chemical formula for Butane: CH3CH2CH2CH3 or C4H10

1) The molar mass of Butane: 4 C = 4(12)/ 10 H = 58 g/ mol


Procedure:
1) Fill the sink full of water


2) Weigh the butane lighter to the nearest 0.01 g


3) Submerge the 100 mL Graduated Cylinder into the sink, making sure it fills completely with water and then invert it (there shouldn’t be any air bubbles).


4) Place the lighter at the bottom of the sink (make sure it is completely beneath the water), underneath the graduated cylinder


5) Hold down the button of the lighter to release butane and fill the graduated cylinder between 10 and 20 mL (It will displace the water)


6) Remove the lighter, wrap a paper towel around it and shake it so any water that got inside the lighter will come out


7) Weigh the butane lighter once more. If the mass is heavier than it started, it means that there is still water inside and you will still need to try and shake it out.

Observations: We first filled the graduated cylinder completely with water in a sink, inverted it and made sure that there were no visible bubbles. When we placed the lighter underneath the graduated cylinder and held down the button, we saw bubbles beginning to rise inside and about 20 mL of the water was displaced. After we removed the lighter, placed it inside the paper towel and shook it a bit, we took it to the electronic scale to be measured. We noticed that the mass of the lighter was greater than when it started, so that meant that there was still water inside the lighter. So, we shook the lighter more vigorously and then measured it to find that the total amount of butane used in the experiment was 0.04 g. We had time to try the experiment once more and came up with similar results.

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We're all part of different groups, but here's one sample of the results:

Analysis:
1) Mass of the butane lighter before the experiment: 16.48 g

2) Mass of the butane lighter after the experiment: 16.44 g

3) Mass of butane used in the experiment: (Mass of butane lighter before experiment – mass of butane lighter after the experiment) 0.04 g

4) Number of moles of Butane: 0.04 g x 1 mol/58 g = 6.9 x 10 to the power of -4 mol

5) Molar volume of Butane: L/1 mol = 20 mL/6.9 x 10 to the power of -4 mol = 28985.5 mL/mol.

28985.5 mL/1000 = 28.99 L/mol

Conclusion:
1) Percent Error (Measured-Accepted/Accepted x 100): 28.99 L – 22.4 L/22.4 L = 29.4 %.

2) A number of factors may have affected our results. First of all, perhaps there were some air bubbles inside the graduated cylinder underneath the water. It’s also possible that we didn’t release enough or released too much butane into the cylinder. In addition, we may have not have shook out enough water. Finally, there could be slight miscalculations in recording the mass of the butane lighter before and after the experiment.