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Really easy document, Cheat Sheet of Chemistry

University of OttawaChemistry

very good content about resonance structures

Typology: Cheat Sheet

2019/2020

Uploaded on 01/17/2026

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afrah-abdul-khader 🇨🇦

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Experiment 1: Extraction of a Three-Component Mixture
You should read, and understand, the section on extraction in the Appendix before the laboratory
This experiment has been chosen to illustrate the isolation of compounds from a mixture by
using two immiscible solvents, as well as to introduce you to the separation techniques in organic
chemistry and the concept of solubility.
Often, an extraction method is used as the first step in purification. For example, a desired
compound can be obtained from a mixture or from a natural source through extraction. The
compound obtained is impure, as it is mixed with minor components of another compound; or,
when there is a mixture of two or more components and only one of the components is desired, then
it is impure. The undesirable components are considered impurities. Any remaining impurities are
then removed by a method of final purification—these may include distillation or recrystallization.
Recrystallization is a method of purifying impure solids, while distillation is a method of purifying
impure liquids.
Solvents and Solubility
Solvents play a large role in organic chemistry experiments and are commonly classified in
terms of polarity. The polarity of an unknown compound is estimated by comparing its solubility in
solvents with “known” polarity. For instance, most inorganic ionic salts, and the salts of organic
acids and bases are soluble in water. This brings us to solubility by reaction, which is common in
organic chemistry. Organic acids and bases, as with inorganic analogues, react together to
give water-soluble salts. In general, the functional group of a compound plays a significant role
in determining solubility in a solvent.
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Experiment 1: Extraction of a Three-Component Mixture

You should read, and understand, the section on extraction in the Appendix before the laboratory This experiment has been chosen to illustrate the isolation of compounds from a mixture by using two immiscible solvents, as well as to introduce you to the separation techniques in organic chemistry and the concept of solubility. Often, an extraction method is used as the first step in purification. For example, a desired compound can be obtained from a mixture or from a natural source through extraction. The compound obtained is impure, as it is mixed with minor components of another compound; or, when there is a mixture of two or more components and only one of the components is desired, then it is impure. The undesirable components are considered impurities. Any remaining impurities are then removed by a method of final purification—these may include distillation or recrystallization. Recrystallization is a method of purifying impure solids, while distillation is a method of purifying impure liquids. Solvents and Solubility Solvents play a large role in organic chemistry experiments and are commonly classified in terms of polarity. The polarity of an unknown compound is estimated by comparing its solubility in solvents with “known” polarity. For instance, most inorganic ionic salts, and the salts of organic acids and bases are soluble in water. This brings us to solubility by reaction, which is common in organic chemistry. Organic acids and bases, as with inorganic analogues, react together to give water-soluble salts. In general, the functional group of a compound plays a significant role in determining solubility in a solvent.

These functional groups typically increase a compound’s polarity: Solubility tests are extremely useful in determining the possible functional groups present in an unknown compound. Small amounts of the unknown are used, but the information gained in a short period of time is invaluable. A “solubility chart “is shown below. It is necessary to understand the solubility based on functional groups and to be able to reach appropriate conclusions about structures of unknown compounds based on solubility results

The -COOH, a strong acid, is also soluble in dilute sodium bicarbonate (weaker base): Polar compounds generally dissolve in polar solvents, and non-polar compounds in non- polar solvents (known as the “like dissolves like” concept). The rate of solution of a solute in solvents can also be increased by agitation (shaking or stirring). Finely divided solids usually dissolve faster than large chunks of solid due to their greater surface area. Often a solute appears insoluble, but if left to stand, can later be found to be slowly soluble. SOLVENT BOILING POINT FREEZING POINT POLARITY Petroleum ether Various ranges N Cyclohexene 81 6.5 N Carbon tetrachloride 76 -23 N Benzene 80 5.5 N Chloroform 61 -64 I Methylene chloride 40 -97 I

Acetone 56 -95 P Ethanol 78 -117 P Methanol 65 -98 P Water 100 0 P N=non-polar I=intermediate polarity P=polar A mixture of an acid, base and neutral compound could be separated based on the change in solubility that occurs once the compound has been deprotonated or protonated. Organic acids are often insoluble in water and soluble in slightly polar organic solvents such as ether. However, bases can deprotonate the organic acids to form ionic salts, which are soluble in water but insoluble in ether (solubility by reaction). Strong organic acids are strong proton donors and therefore are the easiest to deprotonate. They will react readily with both strong and weak bases. In contrast, a weak acid is a poor proton donor and can therefore only be deprotonated by strong bases. The acids can be recovered by acidification, which will protonate the compound, allowing it to precipitate out of the aqueous solution and be filtered by vacuum filtration. Similarly, a water-insoluble organic base can be protonated by an acid to form an ionic salt, extracted into the aqueous layer and then recovered by the addition of a strong base. The neutral compound remains in the organic solvent and is recovered by evaporating the organic solvent. Figure 1. Using acid/base chemistry to change the functional groups on compound into charged species so the compounds become polar. Data Sheet A has been completed for you, using appropriate reference books such as the Handbook of Chemistry and Physics (commonly called the CRC Handbook) or the Merck Index.

  1. Again, transfer the aqueous layer into A.
  2. Repeat extraction as above on the remaining organic layer using another 5 mL portion of 1.5 M NaOH.
  3. Combine these aqueous layers (from step 11) into B.
  4. Rinse the sep funnel with 5 mL H2O, and add the aqueous layer into B.
  5. Rinse the organic layer once more with 15 mL saturated NaCl and then drain and discard the aqueous layer. ( What is the purpose of NaCl? )
  6. Pour the organic layer into C.
  7. Add a spatula tip of anhydrous CaCl2 and continue to do so until the CaCl2 appears loose (snow globe effect).
  8. Once step 16 is completed, decant the organic layer (C) into a pre-weighed 100 mL beaker (A’).
  9. Wash the remaining contents of C with 3 mL ether, and add ether wash into A’.
  10. Add boiling chips (2-3 is fine) into A’, then evaporate the ether layer by heating A’ in a hot water bath (Obtain a larger beaker, fill it to 1/3 with tap water, and boil the water. Place beaker with A’ into the beaker with hot water). If it is short on time, evaporate directly on the hotplate using boiling chips but BE CAREFUL NOT TO HEAT TOO HIGH.
  11. Once the organic layer has evaporated, remove the boiling chips, then weigh the contents A’.
  12. Discard the contents of beaker A into the proper waste bottle.
  13. Recall B from steps 12 and 13. Acidify B with concentrated HCl to pH < 3. Again, use pH paper to test the pH.
  14. After precipitate forms, proceed to vacuum filtration. Vacuum Filtration
    1. Obtain the Buchner flask and funnel and a filter paper that exactly fits the funnel.
    2. Connect the thick-walled vacuum tubing to the side arm of the Buchner flask and the side-piece of the front tap at your work sink.
    3. Clamp the neck of your Buchner flask to a retort stand. Turn on the tap fully. Use a small amount of the solvent being used (in this case cold water) to wet the filter paper and suck it down fully over the funnel holes. Pour your solution into the funnel.
  1. When the filtration is complete, first remove the vacuum tubing from the yellow tap, and then turn the tap off (why?).
  2. Place each solid in a pre-weighed plastic bag, weigh the recovered compounds, calculate your percentage yield and fill out the product label and attach it to the product in a plastic bag. Submit all necessary material to your TA. NOTE: Remember to fully label ALL compounds and hand in to your TA. Pre-lab questions:
  3. How do you know which layer (aqueous or organic) will be on the bottom? On the top?
  4. Write the solubility by reaction equations for organic acids and bases.
  5. How can you make an organic acid soluble in water? How about an organic base? Once they are dissolved in water, how can you recover the original organic acid or base?
  6. How would you know that pressure is present in your separatory funnel when you are venting? How would you know that there was no more pressure?
  7. You are working with very concentrated hydrochloric acid. What are some dangers when working with concentrated acids? References: (1) PubChem. Acetanilide. Nih.gov. https://pubchem.ncbi.nlm.nih.gov/compound/Acetanilide#section=Uses (accessed 2024-07-24). (2) Murov, S. Experiments and Exercises in Organic Chemistry: A Challenge Oriented Approach; http://murov.info/orglab/11-e6.pdf. (3) Experiments and Exercises in Organic Chemistry Lab Book. Murov.info. http://murov.info/orglab.htm (accessed 2024-07-26).