Lesson 2 Lab: Weighing on an Analytical Balance & Distillation
Begin by viewing the following Thinkwell video
After you watch the above video, answer the questions below in sufficient detail:
(a) (2 pts) What are the features of an electronic balance? Include all of those discussed in the video.
Answer: Professor Gordon Yee notes that an electronic balance has different features such as electronic read-out and the tare. However, other analytical balances have features such as custom LCD display with seven alphanumeric characters, ergonomic leveling system, cursor keys for navigation through menu, one function per key, stability levels, filters, stability indicator, auto-zero tracking, weigh below capability, menu and calibration lock-out switch, factory reset options, spill gutter and removable draft shield doors (Precision weighing balances, 2012).
(b) (1 pts) What does “tare” mean? What is the importance of the ability to 'tare' when taking the mass of your sample?
Answer: The tare is useful in resetting the weight to 0.0000g hence, allowing weighing by difference. The tare is important because it helps to weigh the weight of the sample not the weight of the sample and the container.
(c) (2 pts) What is the difference between weigh boats and weigh paper, and in what circumstances should you use each?
Answer: According to professor Gordon Yee, weigh boats or filter paper can be used as carrying vessel of the chemical to be weighed. Professor Gordon explains that Weigh boats are containers used to prevent reagents from contacting the balance pan. On the one hand, Professor Gordon notes that a filter paper is a cheaper version of the weigh boat. Weigh boats or filter papers are made of polypropylene, a plastic that does not adsorb water. Filter paper is typically inexpensive compared to weigh boats. Weigh boats do not need to be handled with care. Also, filter papers can help all the material down into the crease and direct it easily into the vessel being used without spilling.
(d) (2 pts) What is the difference in how you weigh smaller amounts vs. larger amounts, and what is the role of the scoopula in this? Explain.
Answer: The role of the scoopula is to help transfer solid materials. For example, professor Gordon used a scoopula to transfer potassium permanganate from a container to a weighing vessel for measurement purposes.
(e) (1 pts) What is the difference between “accuracy” and “precision”?
Answer: According to professor Gordon, accuracy is a degree of agreement between a measurement or a group of measurement and the actual value of a given quantity whereas precision is the reproducibility of a measurement of a given quantity (Thinkwell, 2012).
(f) (2 pts) Suppose that your instructor gives you two samples and claims that they are both calcium sulfide (CaS). Through a series of tricky chemical reactions, your instructor has you decompose both samples into the constituent calcium and sulfur, and you weigh each of your sample components on the analytical balance. You find that one sample produced 6.30 g Ca and 2.54 g S, while the other produced 3.40 g Ca and 1.90 g S. Are these results consistent with the law of constant composition (see Chapter 5)?
Answer: Mass Ca / Mass s 6.30g/2.54g = 2.48
Mass Ca / Mass s 3.40g/ 1.90g = 1.79
These results are not consistent with the law of constant composition, so the information that the two samples are the same substance must therefore be in error.
Please watch the following Thinkwell video:
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?
Answer: The basic concept behind the technique of distillation is separating a mixture of liquids or vapor mixture of two or more substances into fractions of desired purity by the removal of heat. According to professor Gordon, distillation works because of the fact that the vapor of a boiling mixture can contain more components that have lower boiling points. For example, in the experiment when the vapor is condensed, it contained more of volatile components, which would make the original mixture contain lower volatile material.
(b) (2 pts) Describe the apparatus and setup for a distillation. Include all components.
Answer: The components of the apparatus include columns, adapters, condenser, a reflux, reflux drum, reboiler, ring clamps,the feed and heat source. To setup a distillation station one has to begin with the round-bottom flask. To secure the flask, one can use three-pronged clamp, two rings stand and a ring stand. Place the ring clamp and three-pronged clamp on the ring stand. As observed on the video, the ring clamp goes on the bottom and will hold the heat source. Also, you need a Y-adapter secured on top of round-bottom flask. According to the university of Colorado (2012), the Y-adaptor sits on top of the round-bottom flask and then the condenser will secure the Y-adaptor to the system. Both the Keck clip and versatile clamps are also needed. The vacuum adaptor should be connected to the condenser and secured to the Keck clip. Then the steamed funnel should be placed on top of the Y-adaptor followed by pouring the liquid to be distilled. Professor Gordon notes that the flask should be between ½ and 2/3 full and when done one should remove the funnel. At this stage add the thermometer adapter and the thermometer. Professor Gordon notes that the thermometer should be added last because it is large and can break. At this point, one can place the heat source on the ring under the round-bottom flask and start heating.
(c) (2 pts) Imagine that you wanted to perform a distillation at your own home, 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?
Answer: Lets say I wanted to distill lemon water at my house. I would get two containers. I would make sure one of the containers is transparent. I would fill the transparent container with lemon water then join it with the other container at the neck.
I would go a head position the container so that the one with lemon water in it is in the sun that way it can heat up. I would also make sure the other container is kept cool in the shade and angled so that distilled lemon water will collect at the bottom. In my experiment, the heat causes evaporation of the lemon water in the filled container, which then condenses in the cooler container and then collects as distilled water in the bottom of the container.
(d) (1 pts) What is the difference between fractional and simple distillation? What is meant by “theoretical plates”?
Answer: According to the University of Colorado UC (2012), fractional distillation is the process of heating up a mixture containing different substances with different boiling points, and drawing the different fractions off as they each boil and liquefy at its own level. On the other hand, simple distillation is a process of distillation that can be used in separating liquids that have varying boiling points such as liquids that vary between 10-20 degrees. According to the university of Colorado UC (2012), liquids that have lower boiling points distill first and the other liquid component is left behind. In this process, vaporization and condensation occur side by side (UC, 2012).
A theoretical plate is a stage at which two phases of liquid and vapor phase of a given substance can reach an equilibrium point with each other. In an experiment, the more the theoretical plates the more the efficacy of the separation process.
(e) (1 pts) What is meant by “bumping”? What is meant by “reflux”?
Answer: Bumping is a process in which a solvent becomes superheated hence releasing large vapor bubble and explosively forcing liquid outside of a flask.
A reflux is continuous boiling of a solution in a flask where the evaporating solvent is cooled and returns to the original reaction flask (UC, 2012).
(f) (3 pts) Suppose you performed a distillation of a solution containing butyl alcohol (C4H10O, also known as 1-butanol), sec-butyl alcohol (C4H10O, also known as 2-butanol), and ethyl alcohol (C2H6O). Butyl alcohol and sec-butyl alcohol 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, analyze it, and determine that it has a formula mass of approximately 74 amu. What is the identity of this second product that you collected? How do you know? (HINT: You will find the table at http://www2.stetson.edu/~wgrubbs/datadriven/petermurphy/flame/table1.htmlvery helpful when answering this question!)
Answer: Based on the assumption, we can see that Butyl alcohol (C4H10O) has a higher boiling point of than ethyl alcohol (C2H6O) . This is why ethyl alcohol would be collect first before butyl alcohol. In other wards, ethyl alcohol has a lower molecular mass of 46.1 amu than that of Butyl alcohol, which is approximately 74 amu. This is why it is concluded that the mass of the second product collected is butyl alcohol.