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Intermolecular attractive forces
a. As the number of hydrocarbons increases the boiling and melting point increases
second weakest force, a bond with a slight charge separation is called polar, increase intermolecular force
a. Electronegative atoms such as nitrogen, oxygen, fluorine, or chlorine must be present- these atoms pull electrons toward themselves making their end of the bond slightly negative and carbon end slightly positive
1. force between a positive and negative ion such as NaCl( high melting point),
a. Acetic acid could form a salt which is a type of Ionic Attractive Force , that has a high melting point, the H on the OH of the acid is (H donating), when it reacts with a base)
An insoluble impurity such as sodium sulfate would have no effect on the melting point of a compound; the impurity has to be soluble to affect the compounds melting point.
One could prove that the test tubes contain three different chemical compounds by applying the principle that a mixture of two different organic compounds will have a lower melting point than each of the two compounds in its pure form. Therefore, if A and B are different compounds, then the mixture of A + B will have a lower melting point than purely A or B.
The observed melting point temperature will have a broader ranger than the actual melting point temp. This is a result because rapid heating causes the temperature to increase faster than the substance is able to reach thermal equilibrium.
This would result in the sample containing impurities, and therefore, the observed melting point would be lower and over a broader range than the actual melting point of the pure compound.
The melting point sample should be finely powdered so that the sample can heat evenly and therefore a more accurate reading of melting point can be observed. Also, you want it to fit in the capillary tube nicely without it getting stuck.
Packing the sample tightly allows for proper heat transfer and thus even heating. The tightly packed sample heats uniformly, giving a smaller range for melting point. If the sample were not packed tightly, air pockets would prevent heat flow, and this uneven heating would result in a broader melting point range.
a ) Adding an equal quantity of pure acetanilide would result in a higher melting point temperature as well as a smaller range since adding the pure acetanilide would decrease the percent of impurities in the sample.
b ) The addition of benzoic acid would increase the percent of impurities in the sample, which would result in a lower and broader range for the melting point.
Impure compounds will have a _____ melting point range and a ______ melting point. The more impure a substance is the lower and broader the letting point , ratio comparison 1:1, 4:1,1:4
Activated Carbon should be used during recrystallization because it is effective in soaking up pigments and impurities. Activated carbon is used to remove the colored impurities that may be present in the sample. Activated carbon has an increased surface area and a porous surface, allowing it to trap impurities.
Gravity filtration rather than suction filtration is used to remove suspended impurities and charcoal form a hot solution because in vacuum suction filtration you reduce the boiling point of the solvent quicker. If this happens then you would be taking away a lot of vapor rather than liquid causing some of your product to evaporate (decreasing temp quickly, increasing solute concentration, causing precipitation)
The final product is isolated by vacuum filtration because it will remove solvent more effectively than gravity filtration. In addition, vacuum filtration is a much faster process, which is important because once crystals have formed, it is essential to remove the solvent as quickly as possible to prevent it from warming back up and redissolving some of the product.
Beakers have a wide surface area which causes hot liquids to be more volatile because they can cool faster, and this can lead to uneven recrystallization. Also, because the experiment requires the swirling of solvents, a beaker would be a poor choice due to contents splashing out.
From the plots of the boiling point versus the volume of distillate in simple distillation experiment, I could conclude that my products are pretty pure because there is multiple constant points near the actual boiling point of cyclohexane and toluene. But they could be purer since my cyclohexane started to distill out at 81 C instead of 83 C. same with my toluene which stated to distill out at 105 C instead of 111C. This means there must be impurity in the product
The effect on boiling point of a solution produced by a soluble non-volatile substance such as NaCl(on water) is that the boiling point should increase. With an insoluble substance the boiling point should be unaffected. The temperature of the vapor above the sand and water solution should be equal to the boiling point of water, while the vapor temp above the NaCl and water solution will be higher since NaCl is soluble in water, it will raise the boiling point of water.
When water is distilled, it does not vaporize all at once. When the BP is first reached, some water molecules evaporate out; this results in a decrease in both the temperature and the kinetic energy of the remaining liquid. Therefore the remaining water needs to be heated again before water molecules can evaporate.
The running condensate causes the already made vapor to reboil while running down the fractioning column. Each time this happens the liquid is richer and more volatile
It is extremely dangerous to attempt to carry out a distillation in a completely closed apparatus because vapor takes up more space than a liquid. Therefore, under these conditions, the vapor pressure would build up eventually causing the apparatus to explode.
Water enters the condenser at the lowest point and leaves at the highest point because this allows water to completely fill the condenser without leaving air bubbles behind. It is crucial for the condenser to push out all the air and completely fill with water in order for the vapor to condensate properly.
2,5- dinitrophenol= lower PKa (5.15) than carbonic acid, making the 2,5 - dinitrophenol =stronger acid of the two. 2,5- dinitrophenol can protonate the HCO3, leaving 2,5-dinitrophenol negatively charged. Therefore, 2,5-dinitrophenol dissolves in HCO3 sol'n.
is the most important method for purifying solid organic compounds, a pure crystalline organic substance is composed of a three-dimensional array of molecules held together by London forces
Process: Dissolving material to be purified( the solute) in a appropriate hot solvent to yield a solution solubility. As solution cools it becomes saturated with respect to solute, which then recrystallizes. AS crystals form the impurities become excluded.
Pure compound- nice and shiny
Impure- powder like
Heat- helps with solubility
Ice- helps with recrystallization
Charcoal- absorbs impurities
How to choose a solvent
1. Like dissolves like- polar solid/ polar solute
2. Solvent should dissolve impurity but not the compound
3. Most often it is a mixture of solvents
- involves boiling a liquid in a vessel and directing the resulting vapors through a condenser, in which the vapors are cooled and converted to a liquid that flows down into a collecting vessel. Simple distillation is used to separate 2 liquids from each other that differ at least by 75C degrees in boiling point. The closer the boiling points the harder the separation.
- a fractioning column is involved, this helps with liquids that are much closer in range than 75 degrees Celsius. * The column is packed with material that provides a large surface area for heat exchange between the ascending vapors and the descending liquid
Heat exchanges between ascending vapor and descending liquid
Looking for a complete equilibrium and a steady distillation rate at which the distillation is carried out
For distillation 2 liquids should be soluble in one another. If they aren’t then extraction would be the proper way to do the experiment.
Properties of Extraction solvents
-Shouldn't react with the solute or other solvents-Shouldn't be toxic or highly flammable
-Shouldn't be miscible (forming a homogenous mixture) with water-Not all solvents meet all criteria but some come close
Reactions (The technique of Neutral L/L extractions)-(4 steps in order include-
I. Mixing the layers
II. Separating the layers
III. Drying the organic layer
IV. Removing the solvent
1. Sodium Bicarbonate solution is often used to neutralize acids when carrying out a acid base extraction. * if large amount of acid needs to be neutralized with bicarbonate the process should be done in a beaker*
Making the aqueous layer slightly ionic
The organic solvents used for extraction dissolve
Involve carrying out simple acid/base reactions to separate strong organic acids, weaj organic acids, neutral organic compounds and basic organic substances
Substances used; benzoic acid, phenol, naphthalene and aniline
Liquid/ liquid extraction
Reactions are typically
Organic reactions often yield
When a reaction is complete it is necessary to do a workup
o Work up- separate and purify the desired products from the mixture of byproducts and residual starting material
o In L/L extractions a work up in essential, which is followed by purification of the product.
Two types of L/L extrations
· Organic products are often separated from inorganic substance in a reaction mixture by L/L extraction with an organic solvent
t-butyl methyl ether , which 1-bb is soluble in and water and sodium sulfate is not, the layers separate and you take out the proper layer ( methyl ether is less dense then water, organic layer is on top)
Sodium carbonate is added to ensure the acidic substances remain water soluble and that caffeine will be present as the free base to create a extraction medium.
Dichloromethane is used so that caffeine can be extracted from water.
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