lab exam 1
At what temperature did naphthalene start melting? 77.6 ºC 76.3 ºC 75.9 ºC 75.4 ºC
75.4 ºC
How many carbon atoms are in 1,2 - dimethyl hexane? 6 8 5 7 9
8
Fractional distillation cannot separate which of the following? Ethanol + water Crude oil Acetone + water Separation of different gases from air
Acetone + water
Select the functional groups that are present in acetyl salicylic acid (aspirin) Carboxylic acid Carboxylic acid Ester Benzene All of the above None of the above
All of the above
What happens when you add 2-naphtol acid gets deprotonated and migrates to the aqueous layer Benzoic acid and 2-naphtol both get deprotonated but stay in the organic phase Benzoic acid gets deprotonated and migrates to the aqueous layer It has no effect on the solution Benzoic acid and 2-naphtol both get deprotonated and migrate to the aqueous layer
Benzoic acid gets deprotonated and migrates to the aqueous layer
Before shaking the separatory funnel containing the soda, what do you need to ensure? No emulsions are forming Use sugarfree soda Which end you point upwards Both ends are closed
Both ends are closed
Why is it beneficial to have a capillary tube made of glass? Glass is transparent and has good resistance to heat It won't react with the components inside the machine It is a preference, it can be made from plastic It's lighter material
Glass is transparent and has good resistance to heat
Can you spot the correct statement for CH4 (methane), H2CO (formaldehyde), and CO2 carbon dioxide? They are all organic molecules The carbon atoms are different sizes The valence of carbon is changing The angle of the carbon bonds is different
The angle of the carbon bonds is different
Why do we shake the separatory funnel? You can't separate things that are not mixed Because Dr. One told me to To make the surface between the two liquids as large as possible To separate the two phases
To make the surface between the two liquids as large as possible
Why do we vent the separation funnel? To avoid the liquid becoming carbonated To avoid contamination To release a build up of pressure To remove aerosolized caffeine
To release a build up of pressure
The melting point of pure Aspirin is 135°C and the melting point of our sample is 155°C, and the substance purity graphs do not match. Is our Aspirin sample pure? You can view the graph comparing both samples by clicking the VIEW IMAGE button. No I don't know Yes We would need to do more analytical techniques to confirm
no
A piece of ice at 0 degrees Celsius is dropped into the water at 0 degrees Celsius. The ice will then _____. partially melt not melt convert to water melt
not melt
The chart below shows boiling point-composition curves for a mixture of liquids A and B. What is the temperature at which a solution that is 60% A and 40% B will boil? 108°C 110 °C 130 °C 100 °C
108°C
When carbon binds to four other distinct atoms, what is the angle of the carbon bonds? 120° 109.5° 180° 90°
109.5°
The graph shown is a boiling point-composition curve for a mixture of cyclohexane and toluene. The lower curve is the liquid curve and the upper curve is the vapor curve. If a mixture consisting of 30 % cyclohexane and 70 % toluene were distilled in a fractional distillation apparatus having 2 theoretical plates, what would the composition of cyclohexane be in the first drop of distillate? 12% toluene and 88% cyclohexane 88% toluene and 12% cyclohexane 70% toluene and 30% cyclohexane 50% toluene and 50% cyclohexane
12% toluene and 88% cyclohexane
What is the O-C-O bond angle in the HCOO- (formate ion)? 90 60 109.5 120 180
120
Calculate the theoretical yield of acetylsalicylic acid from 2.01 g of salicylic acid assuming excess acetic anhydride. MW of salicylic acid is 138.12 MW of acetylsalicylic acid is 180.15 MW of acetic anhydride is 102.09 2.62 2.01 1.31 3.62
2.62
What is the valence value of carbon? 2 6 8 4
4
A student obtained the following data as listed in his data sheet. Moles of Salicylic acid: 0.0150 Moles of acetic anhydride: 0.0423 Mass of aspirin collected: 1.68 g What is the Percent yield %? 100% 52.09% 66.22% 33.11% 75.23%
66.22%
Using the data below, calculate the vapor pressure of chloroform over a chloroform-benzene solution at 25°C, which contains 59.6 g CHCl3 and 59.6 g C6H6. Assume the solution behaves ideally Vapor pressure of benzene (C6H6) at 25°C = 94.4 torr Vapor pressure of chloroform (CHCl3) = 172.0 torr 37.3 torr 68.0 torr 104 torr 86.0 torr
68.0 torr
What is the mole percent of water in the solution that you are distilling? assume, that the solution in the distillation flask is 3 moles of water and 1 mole of glycerol. 75 mole percent water 80 mole percent water 20 mole percent water 40 mole percent water
75 mole percent water
If we started the purification process with 2 g of naphthalene, and we have recovered 1.8 g, what was the recovery efficiency of the process? 55% 75% 20% 90% 45%
90%
What is the relationship between the following compounds? They are different compounds None of these choices are correct. they are optical isomers They are identical they are cis and trans isomers
????? google it
elect the structure of aspirin. C A B D
A
Select the statement that applies to the eutectic point. A The lowest possible melting point over all the mixing ratios of the constituents At the eutectic point both components of the mixture freeze and melt together as if they are the same Eutectic mixture is dependent on temperature. Only A and B All of the above
All of the above
The purity of a compound can be confirmed by ____. spectroscopy chromatographic technique its melting point and boiling point All of the above
All of the above
What are some common visualization methods used in Thin-Layer Chromatography? UV light Anisaldehyde stain Iodine stain Ninhydrin stain All of the above None of the above
All of the above
Which of the following qualities is necessary for a proper recrystallization solvent? The compound should be very soluble at the boiling point of the solvent and low soluble in the solvent at room temperature The solvent should not react with the compound being purified. The solvent should be volatile enough to be easily removed from the solvent after the compound has crystallized. All of the above A and B
All of the above
When is it a good idea to use vacuum distillation? All of these reasons If the components are not thermostable and might decompose at higher temperatures If you want to speed up the distillation process If the components have high boiling temperatures
All of these reasons
A liquid mixture boils without changing constituent is called_____ complex Binary liquid mixture Azeotropic liquid mixture Zeotropic liquid mixture Stable structure
Azeotropic liquid mixture
Which of the following molecules do you think would be the correct reagents to perform an esterification reaction? A and C C and D B and D A and B
B and D
Why is it important to wait until the crystals are dry before calculating the yield? Because water will react with the product Because water will form hydrogen bonds with the product Because otherwise the mass of water will add weight on the scale Because the molecular mass of water will influence the yield
Because otherwise the mass of water will add weight on the scale
Based on your newfound knowledge of interactions. Which of these compounds do you think will have the higher Rf value, and why? Benzene - because it will not interact via hydrogen bonding, and have a weaker adsorption Phenol - because it will have a greater interaction with the mobile phase Phenol - because it will interact with hydrogen bonding and have a stronger adsorption Benzene - because it is more soluble than phenol
Benzene - because it will not interact via hydrogen bonding, and have a weaker adsorption
From the compounds below, what is the name of the compound with 4 carbons? Ethene Ethane Ethyne But-2-ene
But-2-ene
Why can the caffeine transfer from the aqueous phase to the organic phase? Caffeine has a higher relative solubility in dichloromethane than in water Dichloromethane has a higher density than water, thus caffeine precipitates into the lower phase Caffeine is not an organic molecule Caffeine has a lower relative solubility in dichloromethane than in water
Caffeine has a higher relative solubility in dichloromethane than in water
Do you remember the definition of an organic compound? From this image, which compound would you say is not considered an organic compound? Calcium carbonate Benzene Vitamin C Neither of them
Calcium carbonate
Compound A has an Rf = 0.35 and compound B has an Rf = 0.64 when spotted on a silica gel TLC plate and developed with hexane. Which compound is more polar? Compound A Compound B Both have the same polarity. It cannot be determined.
Compound A
Now, based on your knowledge of TLC and the polarity of the compounds, which sample do you think will travel the furthest? Compound B - Polar Compound A - polar Compound A - Non-polar Compound B - Non-Polar
Compound B - Non-Polar
The process to cool-down a solution can be accelerated by using a ice bath, but why shouldn't we do this when the mixture is still hot? Cooling too quickly might trap impurities in the crystals The crystals won't form if it cools down too quickly We could have too many crystals if we cool it down too quickly We could do it, there is no reason to wait until it is at room temperature
Cooling too quickly might trap impurities in the crystals
A non-volatile impurity will _______ the vapor pressure of a liquid and _______ the boiling point. Not affect, not affect Increase, increase, Decrease, decrease Increase, decrease Decrease, increase
Decrease, increase
Consider the following solvent pairs. If mixed together, which pairs would form two layers? Water and ethanol Hexane and heptane Methane and water Butyl alcohol and ethanol Dichloromethane and water
Dichloromethane and water
Which of these phase changes occur during distillation? Condensation, then evaporation Evaporation, then condensation Melting, then freezing Sublimation, then condensation
Evaporation, then condensation
A simple fractional column tube is packed with: Wooden beads Plastic beads Glass beads Metal beads
Glass beads
The recrystallization solvent must dissolve a large amount of solute at: High temperatures All temperatures Low temperatures Room temperature
High temperatures
How would you know if your product is pure from the melting point? I only need to examine the crystals for purity I would compare it to the recorded melting point of the pure sample for the compound I have synthesized I need other techniques to see how pure it is It should be a higher melting point than the reactants
I would compare it to the recorded melting point of the pure sample for the compound I have synthesized
In which phase will you find caffeine after the phase separation? In the aqueous phase only It's in both phases In the organic phase only In a quantum layer between phases
In the organic phase only
How does increasing the polarity of the developing solvent affect the Rf of a compound on silica gel TLC plate? Does not change the Rf. Increases the Rf Decreases the Rf It cannot be determined.
Increases the Rf
What is the purpose of the heating chamber in the melting point machine? To make sure the capillary tube does not melt Regulates one set temperature It acts as the heat source to steadily increase the temperature To keep the machine hot at all times
It acts as the heat source to steadily increase the temperature
Do you know where is the correct placement for the mercury bulb of the thermometer in the distillation apparatus? Just on top of the liquid mixture in the distilling flask Just below the opening where the condenser connects to the distilling flask It doesn't matter, as long as it's not submerged in the liquid mixture Submerged in the liquid mixture in the distilling flask
Just below the opening where the condenser connects to the distilling flask
Which graphical method is used to determine the number of theoretical stages required? ichaelis menten plot Eadie hofstee plot McCabe Thiele plot Lineweaver Burk plot
McCabe Thiele plot
Which of these phase changes occur during simple distillation? One cycle of evaporation and then condensation One cycle of condensation and then evaporation One cycle of melting and then freezing One cycle of sublimation and then condensation
One cycle of evaporation and then condensation
Compounds A and B are found in a mixture. Rf values for both compounds were calculated. Which of the following sets of Rf values would reflect the largest separation between A and B? RfA=0.6, RfB=0.5 RfA=0.4, RfB=0.2 RfA=0.5, RfB=0.6 RfA=0.1, RfB=0.1
RfA=0.4, RfB=0.2
In Thin-Layer chromatography, the stationary phase is a gas Solid or liquid Liquid Liquid or gas Solid
Solid
Looking at the distance the spots have traveled up the TLC plate, which compound do you think is the most polar? Reaction mixture No answer text provided. Product Starting material
Starting material
What are some of the factors in your synthesis that can affect the purity of your product? Moisture from the air and wet samples Temperature, solvent, recrystallization, drying, and filtration The type of gloves Solvent and Temperature
Temperature, solvent, recrystallization, drying, and filtration
Looking at this TLC plate, what do you think went wrong? The TLC was removed from the chamber too early The solvent front travelled to far up the plate The samples were not spotted correctly The TLC plate was not placed perpendicular to the solvent
The TLC plate was not placed perpendicular to the solvent
If you were performing the distillation that you did in the laboratory, at 400 meters above sea level, how do you think the initial boiling point of the mixture in the distillation flask would change? The change in boiling point can not be predicted. The boiling point would increase as compared to the boiling point at sea level. The boiling point would decrease as compared to the boiling point at sea level. The boiling point would remain the same as compared to the boiling point at sea level.
The boiling point would decrease as compared to the boiling point at sea level.
if you're heating a homogenous liquid mixture and its components have different boiling temperatures. Which component will we collect first in the receiving flask? The component with the highest melting point The component with the lowest boiling point The component with the lowest melting point The component with the highest boiling point
The component with the lowest boiling point
you're heating a homogenous liquid mixture and its components have different boiling temperatures. Which component will we see first in the collecting flask? The component with the highest melting point The component with the highest boiling point The component with the lowest boiling point The component with the lowest melting point
The component with the lowest boiling point
There is cold water circulating in the condenser, which cools down the hot vapor coming from the distilling flask. How do we avoid thermal shock to the glassware? The cool water enters at the top part of the condenser, closest to the distilling flask, so the cold water can immediately and effectively cool down the hot vapor To avoid thermal shock, the water circulating in the condenser has to be exactly 2°C.degrees celsius Thermal shock doesn't happen to the condenser The cool water enters at the bottom part of the condenser, closest to the distilling flask, so the coldest water doesn't meet the hottest vapor
The cool water enters at the bottom part of the condenser, closest to the distilling flask, so the coldest water doesn't meet the hottest vapor
In the laboratory experiment, When you collect distillate from the H2O/Methanol mixture in the collection flask, what happens to the original mole percent of water in the distillation flask? You cannot determine what is happening to the mole percent of water The mole percent of water remains the same The mole percent of water increases The mole percent of water decreases
The mole percent of water decreases
After performing a TLC experiment, a researcher determines the Rf value of a component to be 2. He also notes that the solvent traveled a distance of 4cm on the plate. What can you conclude about this experiment? The component travelled a distance of 8cm The solvent is not volatile The reported data does not seem valid There are multiple components in the mixture
The reported data does not seem valid
Take a look at this TLC plate on the LabPad, what do you think went wrong here? The samples were too close in polarity to separate Trick question! This is how it is supposed to look The solvent system was too non-polar The solvent system was too polar
The solvent system was too polar
Why do you need to be gentle when tapping the tube on the workbench surface? The tube is made of glass so it can shatter easily You don't want the solid to move all the way down The tube can damage the workbench . It can cause contamination of the sample
The tube is made of glass so it can shatter easily
An unknown white powder with a melting range of 161-163oC was mixed with the following standard compounds and in all three cases its melting range dropped about 15 degrees. What can be said about this compound? salicylic acid: 158 - 160 oC Benzanilide: 161-163 oC Triphenylmethanol: 159.5 - 160.5 oC The unknown is salicylic acid The unknown is Benzanilide The unknown is Triphenylmethanol The unknown is none of the above The unknown can be all of the above
The unknown is none of the above
Before we filter the product, we need to place a filter on the watch glass and tare the scale with it on. Then, after filtering and drying the solid, we will weigh it again. What will we be able to calculate with those two measurements? The water content of the filter The weight of the filter and the naphthalene crystals The weight of the filter The weight of naphthalene crystals
The weight of naphthalene crystals
What is the relationship between the following compounds? They are different compounds One is an alkane and one is an alkene They are identical They are constitutional Isomers
They are constitutional Isomers
Assume you just weighed out 2 g of naphthalene and it looks red. Why do you think that is? It's an optical illusion, it is actually white This naphthalene contains red impurities It looks red because we have a large amount of it on the weighing dish Naphthalene can have many different colors
This naphthalene contains red impurities
How does the sample interact with the TLC plate? Through intermolecular interactions via the surface OH groups The surface of the plate is coated with special silicon glue Through the mobile phase causing the sample to stick to the plate Covalent bonds form between the sample and the plate
Through intermolecular interactions via the surface OH groups
Why do we cover the TLC tank? To ensure the volatile solvent does not evaporate To contain the fumes To make sure that the solvent doesn't accidently spill out To make sure your lab partner doesn't drink it
To ensure the volatile solvent does not evaporate
Choose the incorrect statement from the following options. Two different pure substances have the same melting points. Every pure solid crystalline substance has a characteristic and unique melting point. An impure sample of substance has a different melting point. Melting point serves as the criteria for the purity of a solid substance.
Two different pure substances have the same melting points.
Which compounds seem to have either an alcohol or phenol functional group? Compounds C, D, and E Only compound A Compounds A and D Compounds A, B, and D
WRONG I SAID THIS: Compounds A, B, and D
What is the main information you wish to acquire when performing a melting point analysis in the "Synthesis of Aspirin" experiment? How much reagent has successfully turned into product Whether the conversion from reagent to product was successful The percentage of impurities in your sample The average size of crystals after the crystallization process
Whether the conversion from reagent to product was successful
The functional group contained in the compound CH2=CH2 is a(n) alcohol alkene ester ketone
alkene
What is the name of this compound? octane 3,4 dimethyl pentane 2,3 dimethyl pentane hexane
i think it is the 2,3 dimethyl pentane
A liquid with a high vapor pressure ________. is volatile is Non-volatile cannot be classified as volatile or non-volatile since more data is needed. is a eutectic liquid.
is volatile
What is the hybridization of the carbon atom in the acetylene molecule? sp sp3 sp3d2 sp3d sp2
sp
