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Weighing on an Analytical Balance & Distillation

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(a) (2 pts) What are the features of an electronic balance? Include all of those discussed in the video.

Answer: There were two features of an electronic balance discussed in this video. First there is the electronic read out which makes the measurement very accurate and the tare feature which can reset the balance to zero when something such as a container is still on the balance (Yee, n.d., Weighing…).

(b) (1 pts) What does “tare” mean? What is the importance of the ability to ‘tare’ when taking the mass of your sample? Be specific.

Answer: Tare is used to reset a balance to zero in order to get only the weight of a sample, not of a sample and container (Yee, n.d., Weighing…). It is important because accuracy and precision are both very important when measuring. The tare feature makes the measurement more accurate. It also allows just the substance to be measured without the substance having to be put directly on the balance.

(c) (2 pts) What is the difference between weigh boats and weigh paper, and in what circumstances should you use each? Be specific and detailed in your answer.

Answer: Weighing boats are more expensive and they are used to measure larger amounts whereas weighing paper is cheaper and used to measure smaller amounts (Yee, n.d., Weighing…). Weighing boats are small plastic boats and weighing paper are small squares of very thin wax paper that can be folded (Yee, n.d., Weighing…).

(d) (2 pts) According to the lab video, what is the difference in how you weigh smaller amounts vs. larger amounts, and what is the role of the scoopula in this? Explain in detail.

Answer: When weighing smaller amounts weighing paper is used and in weighing larger amounts weighing boats are used (Yee, n.d., Weighing…). The scoopula is used to add reagents to weighing paper and is also used to remove reagents if too much is added to the weighing paper (Yee, n.d., Weighing…). While weighing larger amounts in the weighing boat, you should pour slowly from the container and roll from side to side (Yee, n.d., Weighing…).

(e) (1 pts) Discuss the difference between “accuracy” and “precision”?

Answer: Accuracy is the degree of agreement between a measurement and the actual value of a given quantity and precision is the reproducibility of a measurement of a given quantity (Yee, n.d., Weighing…). So in other words, precision of a value is the measure of reliability of an experiment and accuracy of a value is a measure of how closely the experiment results agree with a true or accepted value (Diffen, n.d.).

(f) (2 pts) Suppose that your instructor gives you two samples and claims that they are both aluminum phosphide (AlP). Through a series of tricky chemical reactions, your instructor has you decompose both samples into the constituent aluminum and phosphorous, and you weigh each of your sample components on the analytical balance. You find that one sample produced 3.85 g Al and 4.42 g P, while the other produced 3.05 g Al and 3.94 g P. Are these results consistent with the law of constant composition (see Chapter 5)?

Answer: When you break down the mass ratio for the produced samples you get the below results:

Sample 1: 4.42 g P / 3.85 g AL = 1.15
Sample 2: 3.94 g P / 3.05 g AL = 1.29

This means that these results are not consistent with the law of constant composition because the law of constant composition states that all samples of a given compound have the same proportions of their constituent elements (Tro, 2011). The results above have different mass ratios therefore conflict with the law of constant composition.


Please watch the following Thinkwell video:

15.1.4 CIA Demonstration: Distillation

After you watch the above video, answer the questions below in sufficient detail:

(a) (1 pts) What is the basic concept behind the technique of distillation? How and why does it work? Be clear and specific.

Answer: Distillation is a method for separating a liquid from a solid or from another liquid in which the liquid is boiled off and then recondensed (Yee, n.d., Distilliation). It works because the substance you are looking to distill is boiled off recondensed and separated. It can be used to purify liquids from solids or from other liquids (Yee, n.d., Distillation).

(b) (2 pts) Describe the apparatus and setup for a distillation. Include all components.

Answer: The distillation apparatus consists of a round bottom flask connected through an adapter to a condenser, which is connected through another adapter to a second round bottom flask (Yee, n.d., Distillation). There is a thermometer connected through the thermometer adapter at the top (Yee, n.d., Distillation). There is also a vacuum adapter and a heating mantle. The heating mantle is a coil which heats through electrical resistance (Yee, n.d., Distillation). You use cold water and make sure that it goes in through the bottom and out through the top (Yee, n.d., Distillation).

(c) (2 pts) Imagine that you wanted to perform a distillation at your own home (remember, distillation as a technique is not illegal—it is only illegal if you use it to produce alcohol), but you did not have the fancy lab equipment that you saw in the video. How could you do it? How could you improvise in terms of equipment? Explain the entire setup in detail and how the parts would work together.

Answer: I would use a cooking pot would I would connect using plastic or copper pipe to connect to a pan which would be used as the condenser. I would attach a thermometer to the first cooking pot. Then there would be a coffee cup for the collection cup which would be connected to the pan using the plastic or copper pipe. The cooking pot would be placed at a higher level so the tubing could be placed downward. These are all items I have at home that could be used to make a homemade distillation apparatus.

(d) (1 pts) What is the difference between fractional and simple distillation? What is meant by “theoretical plates”?

Answer: Simple distillation is a method for separating a liquid from a solid or from another liquid, provided the boiling points of the two liquids are sufficiently separated; whereas fractional distillation is a method for separating two liquids with similar boiling points through use of repeated cycles of boiling and condensing (Yee, n.d., Distillation). Theoretical plates is the surface area available to a liquid in which to condense during distillation, the higher the theoretical plates the better separation allowed (Yee, n.d., Distillation).

(e) (1 pts) What is meant by “bumping”? What is meant by “reflux”?

Answer: Bumping is the eruption of a liquid due to superheating and reflux is the gentle boiling during distillation such that the vapors may continuously condense and boil to maintain the phase equilibrium (Yee, n.d., Distillation).

(f) (3 pts) Suppose you performed a distillation of a solution containing 1-pentanol (C5H12O), 2-pentanol (C5H12O), 3-pentanol (C5H12O), and methyl alcohol (CH4O). All three pentanols here have the same chemical formula, but they do have a different arrangement of their atoms (i.e. they are shaped differently), so this makes them have slightly different properties from one another. During the distillation, you collect the FIRST product that comes out, and set it aside. Then, you collect the SECOND product that comes out, and set it aside Then, you collect the THIRD product, analyze it, and determine that it has a formula mass of approximately 88 amu. What is the identity of this second product that you collected? How do you know (discuss ALL relevant data)? (HINT: You will find the table at http://www2.stetson.edu/~wgrubbs/datadriven/petermurphy/flame/table1.html very helpful when answering this question!)

Answer: The Methyl Alcohol has the lowest boiling point so this compound would come out first. The second boiling point would be 3- Pentanol would be the second product that comes out.


Diffen. (n.d.) Accuracy vs. Precision. Retrieved from http://www.diffen.com/difference/Accuracy_vs_Precision

Tro, N.J. (2011). Essentials Introductory Chemistry (4th ed.) (pg 129). Boston: Pearson Prentice Hall.

Yee, Gordon. (n.d.) CIA Demonstration: Distillation [Thinkwell]. Retrieved from http://my.thinkwell.com/students/content/videos.cfm?#l2087341

Yee, Gordon. (n.d.) CIA Demonstration: Weighing on an Analytical Balance
[Thinkwell]. Retrieved from http://my.thinkwell.com/students/content/videos.cfm?#l2087341

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