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Lab Tips

Molecular Models1

Goal of the lab: We will be examining molecular models of organic compounds. This lab is particularly valuable in understanding isomers.

Materials needed: A Molecular Modeling Kit for Organic Chemistry, such as the one show here.

No human is able to view an atom with his or her eyes alone. While advances in science might change this eventually, for now we are stuck imagining what atoms look like. This kit will allows us to touch and rotate the hydrocarbons we've only seen described and sketched on flat pieces of paper, with atoms represented by circular globes of plastic and bonds represented by thin sticks of plastic. Similar to the way a book gains another dimension when presented as a movie, our favorite hydrocarbons will come to life in this lab. We will construct, deconstruct, elongate, shorten, and rotate hydrocarbons all in 3-D. The atoms found in the kit are "scaled to size" in proportion to each other, allowing for first hand visualization of the size difference between different atoms.

Preparation: Review, or have a cheat sheet of, the structure of the major functional groups (alcohol, carboxyl, ester, ether, amine, ketone, aldehyde) and the naming prefixes used in organic chemistry (meth-, eth-, pro-, but-, etc.).

Safety: Please do not try to swallow any of the atoms found in the kit. Otherwise, no chemicals to worry about here.

Procedure: We will be building and naming hydrocarbons in this lab. This lab can be done in groups by creating hydrocarbons for your partner(s) to name, or done alone by working your way through the following list:

1. Build and name all isomers possible for the following formulas:

C6H14 (5 isomers)
C5H10 (6 isomers)
C5H8 (3 isomers)
C4H10O (4 isomers)

2. What happens when Fluorine or Bromine reacts with C5H8? Build and name these isomers as well.

3. Build and name a(n):

  • Alkane with more than 7 carbons
  • Alkane in the shape of a ring. What is the minimum number of carbons needed for this?
  • Alkene with more than 7 carbons
  • Alkene in the shape of a ring. What is the minimum number of carbons needed for this?
  • Alkyne with more than 4 carbons
  • Alkyne in the shape of a ring. What is the minimum number of carbons needed for this?
  • Smorgasbord of hydrocarbons: include a double and a triple bond in the same molecule. What is the minimum number of carbons needed for this?

4. Give the molecular formula and build the following:

2-pentanol
3-methylpentane
hexanol
3-ethylhexane
methylcyclopentane
2-butene
3-methyl-1-butyne
2,3,3-trimethyl-4-hexyne
ethanol
3,6-dimethyl-4-octyne
3-ethyl-2-fluoro-1-pentanol
3-butylhexane
1,2-dimethlypropane
2,4-octene
3-ethyl-2-methylpentane
4-heptyne
2-ethyl-2-pentene

Please note that, like acceptance speeches at the Oscars, this list could go on forever. What additional hydrocarbons could, and should, be added to this list?

To Think About:

What happens when you try to make a "quadruple bond?" Why do you think this does not happen in nature? What other combinations seem impossible with the modeling kit?

Video clips:

Here's a brief tutorial on using a modeling kit from a student who loves modeling.

Check out a video on exploring Chiral carbons here.

Organic Chemistry Happens in your Kitchen (and Medicine Cabinet)1

Goal of the lab: Unbeknownst to the general public and smurfs alike, Organic Chemistry takes place all around us. Here we explore chemical and physical changes using ordinary supplies found in most kitchens and medicine cabinets. Armed with this new knowledge, we can then inform our non-Chemist blue buddies on all the organic chemistry reactions they are taking for granted.

Materials needed:

Well plate
Pipette dropper
Stirring rod
Baking soda
Flour
Alka Seltzer
Sugar
Water
Vinegar
Iodine

Preparation: Arrange all your materials on your lab bench or kitchen counter and prepare to be amazed.

Safety: Please do not eat or drink any of the materials in this lab, regardless of how badly you want to.

Procedure:

1. Fill three rows of four wells of the plate with the following:
a. Baking soda
b. Flour
c. Alka-Seltzer
d. Sugar

2. What physical properties do these compounds have? Record these in your lab notebook.

3. Using the pipette dropper, add water to each of the wells in the first row, and observe any observations you see. Please use the stirring rod to bring any reactions to completion (if necessary). Record these in your lab notebook, for prosperity, of course.

4. Repeat step 3 by adding vinegar to the second row of wells. Don't forget to write down all your observations.

5. Repeat step 3 by adding iodine to the second row of wells. Don't forget to write down all your observations.

To Think About:

Think about the differences between physical and chemical reactions. How many of the reactions performed above were physical (size, shape, or phase of matter changed)? How many were chemical (a reaction took place)?

Vinegar is a type of acetic acid. When vinegar caused a chemical change to the samples in the well, what type of reaction was taking place?

Iodine is a halogen. When Iodine caused a chemical change to the samples in the well, what type of reaction was taking place?

Remember that water is a polar molecule, and polar molecules only like other polar molecules. They're sort of like polar bears, that way. What can be said about the compounds that reacted (or didn't react) with water?

What if you were given another row of wells filled with unknown substances? How would you be able to determine that these substances were?

Video clips:

Here are some more organic chemistry experiments you can do using Alka-Seltzer.

Only try this one when outside. 

Hydrocarbons and Energy: Combustion3

Goal of the lab: Thanks to a basic combustion reaction, gas engines are able to run on a supply of hydrocarbons. In this lab, we will examine the most basic organic chemistry reaction that is responsible for making the world run.

Materials needed:

250 mL Erlenmeyer flask
Rubber stopper
Candle
50 mL beaker with limewater (follow this link to make your own limewater)

Preparation: Completely cool the Erlenmeyer flask by placing it in the refrigerator before beginning the lab. This is one Erlenmeyer flask that just needs to chill out for a bit.

Safety: Use caution when lighting the candle.

Procedure:

Light the candle and place the cooled flask over the flame, so smoke from the flame rises up into the flask. After 30 seconds of this, place the stopper in the flask.

Was water produced during the combustion reaction that took place with the burning candle? What supporting evidence is there?

Remove the stopper and add 25 mL of the limewater. If CO2 is present the flask the limewater will turn white and cloudy. Is CO2 present?

What balanced equation describes the results from these two experiments? Use C25H52 to represent the hydrocarbon (candle).

C18H38 + _____ → _____ + _____

To Think About: How does this simple reaction, on a much larger scale, run an engine? Is this reaction endothermic or exothermic? What are the environmental concerns when this reaction is run at a larger scale?

Video clips:

Here is a quick review on combustion reactions (please note all the safety mistakes these students are making. DO NOT try this combustion experiment at home!).

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