chem lab midterm
What is Distillation? What is this technique used for?
-Distillation uses the different boiling points of liquids in a mixture to separate the components. -the process of vaporizing a liquids, condensing the vapor, and collecting the condensate in another container. -the technique is useful for separating a liquid mixture when the components have different boiling points.
How does the concept of "like dissolve like" relate to crystallization? what is the definition of melting point?
If the solute is very polar, a very polar solvent is needed to dissolve it; if it is non-polar, a non-polar solvent is needed. -melting point for a compound is the temperature what which both the solid and liquids phases both exist.
Why should a separatory funnel not be vigorously shaken
It is crucial not to vigorously shake the separatory funnel because it can cause emulsion. Once an emulsion is formed, it is difficult to remove it, and another complex process must undergo to continue with the experiment. An electrolyte will be needed to break the emulsion and then separate the caffeine
What precautions should one use when working with sodium hydroxide?
Sodium hydroxide is a toxic chemical . The compound can be corrosive . Safety goggles are important to wear for protection.
A successful crystallization depends on a large difference between what two things?
between the solubility of a material in a hot solvent and its solubility in the same solvent when it is cold
2. Caffeine is an _________, a subclass of chemically related compounds that all, to varying extents, stimulate the central nervous system and the skeletal muscles.
c. alkaloid
6. Which of the following best identifies why you should not add activated carbon to an already boiling solution?
c. to prevent the "boiling over" by the solution leading to low sample recovery
15. Identify the compound below.
caffeine
Be able to identify the following parts on a simple & fractional distillation apparatus: distilling flask, distilling head, fractional distillation column, condenser, vacuum adapter, and receiving flask
closest picture but use the one on notes for reference
Arrange the following solvents according to decreasing order of polarity (high polar to low polar from left to right) toluene methanol diethyl ether water hexane
hexane<toluene<diethyl ether <methanol<water
7. Which of the following are useful functions served by knowing the melting point of an organic compound?
identify the compound assess the purity
Whats raoult's law what is the formula of raoults law for Ptotal
-Law states that the partial vapor pressure of component A in the solution (PA) equals the vapor pressure of pure A (PAº) times its mole fraction (XA). A similar expression can be written for component B -Ptotal = PA + PB = (XA) (PAº) + (XB) (PBº)
Be able to know how to use a phase diagram for a liquid mixture to give compositions as mole percentages.
1. Horizontal lines represent constant temperatures 2. The upper curve represent vapor composition 3. the lower curve represents liquid composition 4. Pure A will boil at temperature ta 5. Pure B will boil at temperature tb 6. Composition is given as a mole percentage of A and B in the mixture
What are the two cases in which it is possible to get an acceptable separation by using a simple distillation.
1. if the boiling points A and B differ by a large amount (>100), and if the distillation is carried our carefully, it will be possible to get a fair separation of A and B 2. If A contains a fairly small amount of B (<10) a reasonable separation of A from B can be achieved.
what are the two key points to know about crystallization?
1. it is wasteful 2. a crystallization is successful only if there is a small amount of impurity
Identify the simple breakdown steps when doing a distillation
1. the mixture is placed in the distilling flask and contents are heated 2. vapors produced are cooled and re liquefied when passed through a water-cooled condenser 3. once reliquefied they are collected in the receiving flask
A student extracted 1.35 g of crude caffeine from 115.0 g of vivarin. After purification, he obtained 0.75 g of pure caffeine. Calculate the percent recovery of crude caffeine and the percent recovery of pure caffeine based on 115.0 g of tea powder.
1.17% crude caffeine recovery 0.65% pure caffeine recovery
The reaction of 5.45 g of aniline with 15.20 g of acetic anhydride produced 4.25 g of acetanilide. Calculate the percent yield of acetanilide.
53.7
A student extracted 1.25 g of eugenol from the 15.65 g of cloves. Calculate the percent recovery of eugenol based on cloves
7.98 recovered
Using the figure below, estimate the composition of a cyclohexane-toluene distillate that is collected. at 90°C _________________________________ at 100°C _________________________________
90°C - 25 toluene -75 cyclohexane 100°C -65 toluene -40 cyclo
Know how to write the mechanism for the reaction of aniline with acetic anhydride.
Acetanilide is synthesized through the reaction of aniline with acetic anhydride:
What is the process of acidifying a basic solution?
In order to acidify a basic solution, add 5% HCl acid to react with the base. Stir the mixture until the litmus paper indicates it is an acid.
What precautions should one use when working with naphthalene?
Naphthalene is known to be highly volatile. It is highly flammable and can secrete toxins that can make us feel nauseous. It is important to wear safety goggles.
What is the basis of the separation being performed in this experiment? EXP 3
The basis of the separation being performed is a liquid-liquid extraction, which will then be further be done as a recrystallization process to gather the purest form of caffeine.
5. What is the basis of the separation being performed in this experiment? EXP 2
The basis of the separation being performed is liquid-liquid extraction. The liquids present are immiscible, forming the organic and aqueous layers in the experiment.
What would be the purpose of acidifying an organic base solution for an extraction?
The purpose of acidifying an organic base for extraction is to manipulate the solubilities to get two transparent layers. With the change in solubilities using pH, the layers can remove unwanted components and put them into the different layers to be easily extracted.
Explain the reason each step of the separation is performed with three portions of the solvent rather than with a single portion of solvent.
Three portions are necessary for the separation process. When shaking the separatory funnel, the next step is to extract the bottom layer. When you extract the first time, a high percentage of the organic compound can come out of the layer, but still, some can remain in the water layer. Repeating the same process three times is essential to get the remaining substance that you need out. Extraction is a process that needs to be repeated to get the best results and gather more of the desired compound rather than doing it once.
4. What is the process of making an acidic solution basic?
To make an acidic solution basic, adding a basic solution will reduce the acidity. The solution will be shown as neutral; however, it will become a basic solution with the addition of more base components.
Caffeine belongs to a family of naturally occurring compounds called ____as they all to varying extents stimulate what?
Xanthines -they stimulate the central nervous system and the skeletal muscles.
Identification of various functional groups
a
What is fractional distillation? when must it be used
a process that has the effect of many simple distillations. It must be used when the boiling point differences of components to be separated are not large (usually by less than 40)
14. Threobromine is an ------------- which belongs to the class of ---------------
a. alkaloid, xanthines
Caffeine is an ____, a class of naturally occurring compounds containing ___ and having properties of an organic ___base
alkaloid, nitrogen, amine
How is purification affected when the impurities are equally soluble in both the hot and cold solvent?
an effective purification is not easily achieved through crystallization.
acetanilide, aspirin, phenacetin and acetaminophen are mild ___ and. ___
analgesics &antipyretics
what is a drying agent and how do they work? which drying agent was used in lab?
anhydrous magnesium sulfate? brine wash?? to pull water out of the organic layer
Identification of aromatic/non aromatic/ apliphalic compounds
as
9. Why is a finely powered sample preferred to be used during a melting point measurement?
b. it helps to ensure a rapid and efficient transfer of heat through the entire sample
Which of the following are valid reasons as to why gentle shaking is necessary during the extraction of caffeine from tea?
b. the formation of emulsions does not occur c. to prevent the excessive buildup of pressure inside the separatory funnel b and c
From Experiment 3, "Extraction of Caffeine", Caffeine is an _________, a class of naturally occurring compounds containing nitrogen and having the properties of an organic amine base. It belongs to a family called _________.
d. alkaloid, xanthines
8. Which of the following are effects that a soluble impurity has on the melting point of a compound?
d. decrease in melting point; broadening of the melting point range
what is A
distilling head
acetanilide is know as an acylated aromatic amide why?
due to the fact that it has an acyl group substituted on its nitrogen
16. From Experiment 4, "Recrystallization and Melting Point", the separatory funnel should be shaken gently and not vigorously during extraction to avoid the generation of ----------------
emulsions
A drying agent is an insoluble, anhydrous organic salt.
false
Increasing the heating rate does not affect the boiling rate, but increases the boiling temperature of the liquid.
false
______ 1. When mixing reagents using a separatory funnel one should not vent to ensure there is no spill.
false
it is safe practice in the organic chemistry lab to ass boiling chips to an already boiling liquid?
false
what is the definition of melting point range
is reported from the temperature when liquid first appears to the temperature when the sample is completely liquid. the range should be close to the point
what is a simple distillation and it is possible to completely separate a mixture by using it?
it is useful for separating a liquid mixture when the components have different boiling points or when one of the components will not distill. -it is never possible to separate a mixture completely by a simple distillation.
11. Identify the correct chemical name for the structure shown below?
mandelic acid
5. Which of the following best identifies why you should not heat organic solvents over a Bunsen burner flame
most organic solvents are flammable and would ignite if exposed to an open flame
Consider a solution at 100°C where XA=0.6 and XB=0.4 (the vapor pressure of pure A at 100°C is 1010 mmHg & the vapor pressure of pure B at 100°C is 520 mmHg). Would the solution boil at 100°C if the applied pressure were 760 mmHg?
no it would not boil bc the total pressure does not equal the applied pressure
From Experiment 3, "Extraction of Caffeine", in this experiment caffeine is extracted and purified by the process of ________.
none of the above
what are two ways melting points can be used to assess the purity of a mixture?
pure compounds normally have a very narrow melting point and the range should be close to the expected melting point
4. In this experiment caffeine is extracted and purified by the process of ________.
recrystallization
If a mixture contains 2 compounds with one being more volatile (more than 50 degree Celsius) than the other then __________________________ distillation would be preferred.
simple
The stimulation caused by xanthines result in what effects? which xanthine tends to be the most powerful in this respect?
stimulation results in increased alertness, ability to put ogg sleep, and an increased ability for thinking. -caffeine is the most powerful xanthine in this respect
10. What process is occurring when crystals begin to disappear from the bottom of the capillary tube rather than turning into a liquid?
sublimation
How does the packing found inside a fractional column work to separate a mixture of two components?
the column is packed with a suitable material such as a stainless steel sponge or glass beads. - the packaging allows for a mixture of two components to be subjected continuous to many vaporization-condensation cycles as the material moves up the column.
how does the addition of successive amounts of an impurity affect the melting point?
the melting point of a substance decrease with increase in presence of impurities
When the total pressure equals the applied pressure what happens?
the solution boils
at the melting point of a compound what is occurring to the intermolecular forces that hold the molecules together and keep it in its solid state.
they are being broken apart?? they have a high melting point if they are strong IMF
what is an alkaloid
they posses at least one nitrogen atom that can accept a proton by using its lone pair of electrons
Which of the following are valid reasons as to why it is important for one to not overheat the dichloromethane while extracting the caffeine?
to prevent decomposition from occurring to prevent the amount of caffeine is isolated from decreasing (a.) and (c.) only
Given a cyclohexane-toluene distillation graph be able to estimate the composition of the distillate if given certain temperatures.
uhhyes
compounds that have functional groups that can hydrogen bond would be more soluble in which of the six solvents stated above? for compounds that are non- polar?
water&non-polar:ether???
Know the order of polarity for the following solvents: water, organic acids, alcohols, ethers, aromatics, & alkanes
water>organicacids>alcohols>ethers>aromatics>alkanes
"oiling out" referred to what occurrence during crystallization
when the sample melts. when compound is deposited as oil rather than crystals
is caffeine toxic?
yes, if someone drinks around 100 cups of coffee in a short period of time
