Christina SvenssonEmery White, Melissa Love

17.04.09

Mr. PorterSCH3UE- 03

Determining the Molar Mass of Butane

Purpose:Cigarette lighters contain a gaseous fuel that burns quickly. It produces a large amount of heat using only a small amount of gas. In this experiment, the volume and mass of a sample of this gas was measured. Then these data was used to calculate the molar mass of the gas.

Materials:- 4 L plastic pail- 50 mL gas collection tube- disposable cigarette lighter - stopper- funnel- electronic balance- tap water- thermometer

Procedure:1. The striker, flint and spring was removed from the disposable lighter by Mr. Porter2. The 4 L plastic pail was filled with tap water. The temperature of the water was

measured using the thermometer. This temperature was used to approximate the temperature of the gas.

3. The lighter was immersed in water, and then the mass of the lighter was determined using the electronic balance. This mass was used to set a standard for the mass of the wet lighter after being used in the experiment.

4. The gas collection tube was filled with water and turned upside down, after covering the cylinder with a stopper (a hand). It was made sure that there were no air bubbles in the cylinder before removing the stopper. This created a water-filled measuring tube to collect gas.

5. The lighter was held under the upside down water-containing cylinder and the button on the lighter was depressed until enough gas had been obtained.

6. The cylinder was lifted until the water inside the cylinder was on the same level as the water outside the cylinder (in the plastic pail). This was done to equalize the pressure in the cylinder with the pressure in the atmosphere. After equalizing the pressure, the volume of the gas was then read of the cylinder.

7. The lighter was then shaken dry and massed8. The air pressure was given by Mr. Porter

Qualitative Observations:Mass of lighter before completed experiment 18.18 g ± 0.01 gMass of lighter after completed experiment 17.55 g ± 0.01 gVolume of gas in gas collection tube (cylinder) 0.244 dm3 ± 1.0 mm3

Temperature of gas (approximated by the temperature of the air)

301 oK ± 0.5 oK

Air pressure 101.9 KPa ± 0.2 KPaVapour pressure of water 3.78 KPa

Qualitative Observations:Water Transparent, liquid, Butane (C4H10) Transparent, gaseous,

Analysis:1a. ∆ m=mi – mf ∆ m=18.18 g−17.55 ∆ m=0.63

b. P=101.9 ± 0.2 KPa−3.78 KPa P=98.12± 0.2

c.

n=PVRT

n=(101.9 ± 0.2 KPa−3.78KPa )(0.244 dm3)

(8.134 )(301o K)

n=23.941282448.334

n=0.0097786005

2.

M=mn

M= 0.630.0097786005

M=64.42639742 M 64.43 ∑The mass of the butane gas is 64.43 g

Discussion:

In this experiment, butane gas from a cigarette lighter was collected and measured in order to determine the molar mass of butane: the volume and mass of this collected sample of butane gas was measured and used to calculate the molar mass. The theoretical molar mass of butane (C4H10) was calculated, and so was the percentage error between the theoretical value and the experimental value. The experimental molar mass of butane was calculated to be 64.43 g, while the theoretical value was calculated to be 58.12. The percentage error between these two values 13.29 %, which is considered to be a rather high percentage. With these results, the approximate molar mass of butane was calculated. Several improvements could have been done to the experiment. The wet lighter could have been given time to dry to be able to obtain a more accurate mass (since the lighter most likely had a different mass on the two occasions it was massed). The water caused the lighter to have an increased mass, causing an increase in the experimental molar mass of the, leading to a high percentage error. Another improvement that would have made the lab more accurate would be a more accurate reading of the volume of gas in the gas collecting cylinder. A decrease in the volume would lead to a decrease in the molar mass of butane, as an increase in volume would lead to an increase in the molar mass of butane. To improve this, a thinner cylinder could have been used. This would have increased the accuracy in the reading because the gas would be .................................................................................................................................................................................?

Conclusion:3. The theoretical molar mass of butane (C4H10):m=( 4×12.011 )(10 ×1.0079) m=58.123 g/mol The theoretical molar mass of butane is 58.12 and differs from our actual result by 7.727 g. This is quite a lot to be such a light gas, and therefore it is believed that a mistake was done when determining the mass of the lighter after completing the experiment. Since the lighter was wet when massing it, there was no way of determining how much water was still on the lighter. This would have led to a larger value, again leading to a larger uncertainty (see analysis question #4; Percentage Error) then expected.

4. Percentage Error:

% erro r=actual value−theoretical valuetheoretical value

×100 %

% error=65.85−58.12358.123

×100 %

% error=0.1329422088 × 100 % % error=13.29422088 % % error 13.29 %

5. Sources of error:If air was left inside the cylinder, the calculated experimental molar mass of butane would be wrong, since it is no longer pure butane. Also, the air left inside the cylinder might affect the

temperature of the butane gas inside the gas collecting cylinder, causing a higher molar mass. To improve this, a better stopper (than our hands) could have been used). This would cause the air to stay out of the cylinder, and not affect the molar mass of the butane. The reading of the volume inside the gas collecting cylinder could also have been inaccurate, and is a highly valid source of error. If the volume of the gas was incorrectly read, it could lead to either an increase or decrease in molar mass. Write improvementAssuming the temperature inside the cylinder- being the temperature of the butane gas- is the same as the temperature of the air, is also a source of error. A thermometer could have been placed inside the cylinder to ensure an accurate temperature. To avoid affecting the molar mass of butane, the volume of the thermometer would be subtracted from the volume of the cylinder holding the gas. The mass of the wet lighter is not accurate at all. The amount of water being attached to the lighter might, and most likely will, differ on the two occasions being massed. This will lead to an increase in value when calculating the molar mass of butane.

- the mass of lighter not accurate could have dried before determining mass - Bubbles of butane gas could have escaped outside the gas collection cylinder (without us noticing) -

References:Porter, Michael. 15.04.09. Determining the Molar Mass of Butane; AKA “Flick Your Bic™”