OCHEM Lab Final

In the experiment described, the observed reaction rate is equal to the rate constant k multiplied by the concentration of the reactant raised to some exponent. The value of this exponent, represented by x, is the reaction order. rate=k[reactant]^x As such, describe how this equation changes based on order.

For a zero order reaction (x=0), the rate is equal to the rate constant k and is not affected by the concentration of a reactant. For a first order reaction (x=1), the rate increases proportionally with the concentration of the reactant. For a second order reaction (x=2), an increase in reactant concentration causes the rate to increase exponentially.

Are hydrocarbons soluble or insoluble in water?

Hydrocarbons are insoluble in water because they are non-polar. Given that like-dissolves-like and that water is polar, hydrocarbons and water do not mix.

When performing the acid-catalyzed dehydration of an alcohol, the yield of product can be increased by _____________________ during the reaction. The dehydration is _________________, and removing the product from ______________________ reduces the ___________________ reaction.

-distilling off the product -reversible -the reaction flask -hydration Dehydration is a reversible reaction, so the presence of water can reverse the reaction. Because the acid solutions used as catalysts are aqueous, there is water present that could cause the hydration of the product. To prevent this, the product can be removed from the reaction flask by distillation during the reaction. The product is removed from the heat, acid, and water in the reaction flask and reduces the reverse reaction.

In general, when a hydrocarbon is added to water, the hydrocarbon will _____________ the water because hydrocarbons are _______________ than water.

-float above -less dense Hydrocarbons are generally less dense than water so they float on top, like the example of oil on water.

Considering the reaction of bromine with the following alkene: CH3+H-C=C-CH3+H Where would the Bromine attack to join the alkene?

It would break the double bond and bond to the carbons with a free bonding site. This is because Bromine reacts with alkenes by adding across the double bond. Therefore, a bromine is added to each carbon that had participated in the double bond and the double bond is a single bond.

Jones's test, also known as the chromic acid test, shows the presence of?

Primary or secondary alcohols. Jones's test indicates the presence of primary or secondary alcohols by reducing the chromium(VI) in chromic acid to chromium(III). Secondary alcohols are oxidized to ketones. Primary alcohols are oxidized to carboxylic acid by first creating an aldehyde. For this reason, aldehydes also give a positive test. Tertiary alcohols do not react.

Assuming all other factors are held constant, you observe that an increase in the concentration of the reactant in solution causes the reaction rate to increase exponentially. What order of reaction is this?

Second order.

An alcohol with two other carbons attached to the carbon with the hydroxyl group is a?

Secondary alcohol.

An alcohol with three other carbons attached to the carbon with the hydroxyl group is a?

Tertiary alcohol.

When it is time to end a reflux, first ________________ and then turn off the heat. __________________ until the system has cooled.

-lower the heat source -leave the condenser water on The first step in stopping a refluxing system is to remove the heat source. Best practice is to lower the heating mantle or other source first and then turn it off. This order reduces the heat as quickly as possible, which is most important when the reflux is ended due to a safety concern. The water should be left on in the condenser until the glassware has cooled. This helps return any remaining vapors back to the flask.

The term SN1 describes a reaction is a(n) __________________ involving __________________________.

-nucleophilic substitution. -One molecule in the rate-determining step.

Suppose you are titrating an acid of unknown concentration with a standardized base. At the beginning of the titration, you read the base titrant volume as 1.40 mL. After running the titration and reaching the endpoint, you read the base titrant volume as 18.46 mL. What volume, in mL, of base was required for the titration?

17.06 mL To find the volume of titrant used in any titration, subtract the starting volume reading from the final volume reading. The difference between the two readings is the amount of titrant dispensed during the titration. The calculated volume will be an accurate measurement of the titrant required as long as each reading was made as accurately as possible with the meniscus at eye level.

Suppose when reading a buret that you must report your reading with appropriate significant figures. You read that the meniscus is negligibly past the third mark from 17. How should the reading be recorded? -17.4 mL -17.3 mL -17.32 mL -17.325 mL

17.32 mL Determine the volume in the buret based on the bottom of the meniscus. The bottom of the meniscus falls slightly below the third tick mark below 17 mL, which corresponds to 17.3 mL. Therefore, a good estimate of the volume is 17.32 mL. You should always report the reading with one estimated digit past the smallest marking by noticing where the bottom of the meniscus falls between the tick marks.

A positive Baeyer's test appears as?

A brown precipitate. If an alkene or alkyne is present, the brown precipitate of manganese(IV) oxide forms.

A positive Jones's test appears as?

A color change to green. If a primary or secondary alcohol or aldehyde is present, the characteristic blue-green color of chromium(III) appears.

A positive bromine test appears as?

A colorless solution. If an alkene or alkyne is present, the solution becomes colorless as bromine is added across the double or triple bond.

A negative Baeyer's test appears as?

A purple solution. If no alkenes or alkynes are present, the solution remains the purple color of the potassium permanganate.

What is the common name for ethyne?

Acetylene.

Which hydrocarbon group is the least reactive and why?

Alkane groups are the least reactive since they contain only sigma bonds between C-C's and C-H's, which are strong enough to demand high amounts of energy for participation in chemical reactions.

Describe what constitutes an Alkane.

Alkanes only have single bonds, whether in a linear or cyclic formation. Alkanes in a ring formation are often called cycloalkanes.

_______________ are saturated by hydrocarbons.

Alkanes. Alkanes only have single bonds and are saturated hydrocarbons.

Describe what constitutes an Alkene.

Alkenes have at least one double bond. Cyclic alkene structures can specifically be called cycloalkenes.

Baeyer's test, also known as the permanganate test, shows the presence of?

Alkenes. Baeyer's test indicates the presence of alkenes and alkynes through their formation of manganese(IV) oxide when reacting with potassium permanganate in solution.

___________________ are unsaturated hydrocarbons.

Alkenes. Therefore, alkenes and alkynes are unsaturated hydrocarbons.

Describe what constitutes an Alkyne.

Alkynes have at least one triple bond. Cyclic alkynes generally do not exist because of the linear arrangement around the bond.

The bromine test shows the presence of?

Alkynes. The bromine test indicates the presence of alkenes and alkynes through their reaction with bromine.

Why is potassium hydroxide preferred over sodium hydroxide in organic reactions? Select one: -Potassium hydroxide has a higher melting point. -Potassium hydroxide has a smaller cation as the counterion. -Potassium hydroxide is a stronger base. -Potassium hydroxide is more soluble in organic alcohols.

-Potassium hydroxide is more soluble in organic alcohols. Potassium hydroxide is preferable in organic reactions because it is more soluble in organic alcohol solvents, like ethanol, than sodium hydroxide. Sodium hydroxide is a stronger base but that does not matter much if the compound cannot dissolve in the solvent for the reaction.

An SN2 reaction is a type of __________________ in which the nucleophile attacks the electrophile ______________ a leaving group leaves. The rate of the reaction depends on the concentration of ________________.

-Substitution reaction -At the same time -Both reactants An SN2 reaction is a substitution reaction, where a nucleophile replaces a leaving group on the electrophile. The mechanism is concerted, so the attack of the nucleophile and the loss of the leaving group occur at the same time. The concerted mechanism also means that the rate of the reaction is influenced by both the nucleophile and the electrophile.

A negative bromine test appears as?

An orange solution. If no alkenes or alkynes are present, the solution remains the brownish orange color of bromine.

A negative Jones's test appears as?

An orange solution. If only tertiary alcohols or no alcohols or aldehydes are present, the solution remains the orange color of the chromium(VI) in chromic acid.

Describe what constitutes an Aromatic compound.

Aromatic compounds have specific requirements. An aromatic hydrocarbon has carbons in a ring and alternating single and double bonds, which create stability through the delocalization of the electrons. The most common aromatic ring size is six carbons but others do exist.

Assuming all other factors are held constant, you observe that the reaction rate increases in direct proportion to the concentration of the reactant in solution. What order of reaction is this?

First order.

A hydrocarbon is unsaturated if _______________ are present.

any multiple bonds. A hydrocarbon is unsaturated if any multiple bonds, like double or triple bonds, are present.

Which tests can be used to show that a phenol is present? Select one or more: -Lucas test -Iron (III) chloride test -Iodine test -Acidity test

-Iron (III) chloride test -Acidity test The acidity test reacts a base with phenols to deprotonate them and easily dissolve them. In the iron(III) chloride test, a phenol becomes a ligand on iron and changes its color. The Lucas test reacts with secondary and tertiary alcohols. The iodine test shows the presence of starch and should not be confused with the iodoform test.

If crystal growth does not start on its own after the solution in the flask returns to room temperature, identify the best ways to promote this process. Select one or more: -Add ice cubes to the solution. -Add a bit of solid as a seed crystal. -Place the flask on a hot plate to evaporate some solvent. -Scratch the bottom of the flask gently with a stirring rod.

-Add a bit of solid as a seed crystal. -Scratch the bottom of the flask gently with a stirring rod. If crystals do not begin growing after a heated mixture returns to room temperature, try adding a nucleation site. Scratching the flask gently with a stirring rod can create a surface upon which crystals can begin growing. Alternatively, adding a bit of leftover solid material can also start the crystallization process. Changing the temperature or composition of the contents of the flask are not recommended at this point in a recrystallization.

Consider the SN2 reaction of an alcohol with an alkyl halide in the presence of base. The __________ should be added to the alcohol first to _________________ the alcohol and allow it to attack the __________________.

-Base -Deprotonate -Alkyl halide The ability of the nucleophile to properly attack the electrophile depends on the order of addition. The base must be added first to deprotonate the alcohol, turning it into a much better nucleophile that can attack the electrophilic alkyl halide.

Bromothymol blue is an indicator that appears _________ in basic conditions and ____________ in acidic conditions.

-Blue -Yellow

When working in the fume hood, it is important to make an effort to minimize ___________. Only keep items in the hood if they are being used for ____________________. Do not __________ chemicals in the fume hood unless instructed to do so.

-Clutter -The current experiment -Store Substances used within a fume hood are potentially hazardous, and it is important to minimize the risk of accidents or unsafe conditions. Minimizing clutter is an easy way to lower the risk of spilled chemicals and broken glassware. Only bring items in the fume hood if they are needed for the current experiment, and do not store chemicals in the fume hood unless instructed to do so. After an experiment in the fume hood is complete, be sure to return all glassware and chemicals to their proper locations.

In general, when hydrocarbons like oil are added to water, the two liquids ________________ because hydrocarbons are ______________ and water is _________________.

-Do not mix -non-polar -polar Hydrocarbons and water generally do not mix. The hydrocarbons are not soluble in water because they are non-polar and water is polar.

The dehydration of a secondary alcohol, like cyclohexanol, is a mechanism that occurs ______________. First, the alcohol is protonated to _______________________, creating _______________ intermediate. Then, a ______________ is removed, moving the electrons from that bond to make a ____________________ bond.

-In two steps -Leave as a water molecule -A cation -Hydrogen ion -Carbon-Carbon Double The dehydration of a secondary or tertiary alcohol occurs in two steps with an intermediate that can undergo rearrangements. Primary alcohols tend to follow a concerted mechanism, if they react at all. In the two-step mechanism, the first step is the protonation of the hydroxyl group in the alcohol, which creates a positively charged −OH2−OHX2 group. The group then leaves as a water molecule, leaving behind a positive charge on a carbon with three bonds. In the second step, a hydrogen cation is removed from an adjacent carbon, by the conjugate base of the acid. The electrons from the C-H bond can move to between the two carbons, creating a double bond.

Which changes can be made to a chemical reaction in order to increase the rate constant? Select one or more: -Increase the temperature -Decrease the concentration of each reactant -Add a catalyst -Increase the gas constant

-Increase the temperature -Add a catalyst The frequency factor is not affected by changes in a chemical reaction, and the gas constant is fixed. The rate constant can be affected by changes in the activation energy or temperature, however. The most common way to affect the activation energy of a chemical reaction is by adding a catalyst. A catalyst lowers the activation energy, therefore increasing the rate constant. Raising the temperature of a chemical reaction also increases the rate constant.

If the dehydration reaction of an alcohol is successful, what changes would be seen in the IR spectrum for the product compared to the starting material? Select one or more: -The disappearance of a C-O band from the starting material -The addition of a C-C double bond band in the product -The addition of sp3 C-H bands in the product -The disappearance of an O-H band from the starting material

-The disappearance of a C-O band from the starting material -The addition of a C-C double bond band in the product -The disappearance of an O-H band from the starting material In the course of the dehydration reaction, the alcohol is protonated to become a good leaving group in an elimination reaction to form an alkene. The O-H and C-O bonds from the starting material alcohol should disappear in this process. A new C-C double bond should appear in the product. The sp3 C-H bonds are already present in the starting material and no new ones are added, so these bands will not be helpful in detecting the successful reaction.

If the SN2 reaction of an aromatic alcohol with an alkyl halide, like the synthesis of nerolin, is successful, what changes would be seen in the IR spectrum for the product compared to the starting material? Select one or more: -The disappearance of a C-O bond from the starting material -The addition of a C-X band, where X is a halide, in the product -The disappearance of an O-H band from the starting material -The addition of sp3 C-H bands in the product

-The disappearance of an O-H band from the starting material -The addition of sp3 C-H bands in the product In the course of the SN2 reaction, the alcohol is deprotonated and then attacks the alkyl halide to form an ether. The O-H bond from the starting material alcohol should disappear in this process. A new C-O band and C-H bands from the alkyl group should appear in the product. There should be no bond between carbon and a halide in the product, and the bond between carbon and oxygen from the starting material is still present in the product.

What are the concerns presented by overheating a distillation to a dry flask? Select one or more: -The dry flask might become brittle and could easily be broken. -The empty glassware might heat quickly, igniting vapors from the distillation. -The lack of liquid in the original flask might reverse the distillation process. -The remaining solid residue might contain explosive peroxides.

-The empty glassware might heat quickly, igniting vapors from the distillation. -The remaining solid residue might contain explosive peroxides. A distillation should never be overheated to the point that all the liquid is gone. There might be solid residue remaining containing hazardous compounds. Also, without liquid, the glassware would heat more quickly, possibly igniting the vapors still present in the set-up.

Why does the dehydration of an alcohol more often use concentrated sulfuric acid, H2SO4, as the acid catalyst rather than dilute hydrochloric acid, HCl? Select one or more: -Only acids with more than one proton can complete the dehydration reaction. -The presence of the chloride ion could result in a competing substitution reaction. -Hydrochloric acid is too small to effectively react with the alcohol in the reaction. -The additional water solvent from a dilute solution could reverse the dehydration reaction.

-The presence of the chloride ion could result in a competing substitution reaction. -The additional water solvent from a dilute solution could reverse the dehydration reaction. Concentrated sulfuric acid is a good choice for the dehydration of an alcohol because a small volume can be used, with very little water included, and the hydrogen sulfate conjugate base is not a good nucleophile. In contrast, dilute hydrochloric acid does not work well for the dehydration reaction. As a dilute solution, a bigger volume will be necessary, which will add more water to the reaction. If too much water is present, the dehydration reaction could be reversed. Also, the conjugate base, chloride ion, has enough nucleophilic character to possibly cause competing substitution reactions.

For a reaction rate based on one reactant, identify the type of graph that will give a linear plot in each case. Zero order reaction ___________ First order reaction ____________ Second order reaction ____________

-[reactant] vs. time -ln[reactant] vs. time -1/[reactant] vs. time

In general, alcohols _________ when mixed with water because the ____________ in alcohols can ________________ with water.

-dissolve -O-H bonds -hydrogen bond Alcohols generally dissolve in water because the O-H bonds of the hydroxyl group can hydrogen bond with the O-H bonds in water. The interaction allows the molecules to intersperse and dissolve.

Write the balanced equation for calcium carbide (CaC2) reacting with water to give off ethyne (acetylene) when reacted with water.

CaC2 + 2 H2O ---> C2H2 + Ca(OH)2

When working in a fume hood, what is the best position of the hood sash? Select one: -Completely closed -As low as possible, no more than halfway up -At eye level -As high as possible, to the top of the hood

As low as possible, no more than halfway up. Lab participants must have the hood sash raised slightly in order to be able to work in the hood. To ensure safe operation, however, it is important to keep the sash as low as possible during use. This helps ensure that fumes stay safely behind the sash where they can be vented away from users. When the sash is too high, like the image on the left, fumes can escape. When working in a fume hood, try to keep the sash as low as possible, and no more than halfway up. The lower sash helps contain the fumes from the experiment.

What is the best safety approach when working with unknown chemical substances? Select one: -Assume that any substance distributed to lab participants is non-toxic and not a safety risk. -Assume that the substance is hazardous. Always wear appropriate PPE and take steps to prevent contact. -Read the procedure and try to guess what the unknown substance is, then review its specific safety information. -Do not begin working with a substance unless you know exactly what it is.

Assume that the substance is hazardous. Always wear appropriate PPE and take steps to prevent contact. Chemical substances in the lab can be associated with a number of health and safety risks. When working with an unknown substance, the best approach is to assume that the substance is hazardous. Keep the substance away from flames or other chemicals unless instructed otherwise. Always wear appropriate personal protective equipment (PPE) and take steps to prevent contact.

Where should the tip of the thermometer be placed in a microscale distillation set-up? Select one: -Submerged in the liquid of the sample flask -Aligned with the joint between the sample flask and the distillation head. -Completely above the side arm of the distillation head -At or slightly below the side arm of the distillation head

At or slightly below the side arm of the distillation head. The purpose of the thermometer is to measure the temperature of the vapors as they enter the condenser to follow the distillation. Therefore, the tip of the thermometer should be slightly below the side arm of the distillation head, where the vapors travel to the condenser.

What is observed when mixing alkanes, alkenes, and aromatics with one another?

Because they are all non-polar, they all form a homogenous mixture. If even one of them were polar, they would not mix together.

Name a test that could be used to determine if cyclohexanol is present in your product. Give at least one test with some detail of what you would expect.

One way you could test if cyclohexanol is present in your product is to employ the Iron(III)chloride test. When aqueous iron(III)chloride is added into a sample with an aromatic alcohol (such as cyclohexanol), the solution changes from an initial red-orange to purple. If we wanted to test how much cyclohexanol is present, then we would have to set aside a testable amount of product. After doing so, we perform the ferric chloride test and observe the color. If the solution remains red-orange, then there is either no cyclohexanol present or there is a negligible amount. If a noticeable amount resided in the product, then the color of the solution and intensity of it would be dependent on the concentration of cyclohexanol present.

A hydrocarbon is saturated if ______________ are present.

Only single bonds. A hydrocarbon is saturated if it has only single bonds present because each carbon has as many hydrogens around it as possible.

Regarding structure, what typically determines whether a molecule is more polar than another?

Polarity of a molecule increases when the molecule does not have opposing dipoles or a large non-polar section. Molecules or sections of molecules with only carbon and hydrogen are not polar. The most polar molecule in the list is the short alcohol. The ether has dipoles that are symmetrical and decrease the overall polarity. The longer alcohol has a larger non-polar section, which decreases the molecule's polarity overall.

An alcohol with one other carbon attached to the carbon with the hydroxyl group is a?

Primary alcohol.

Describe the complete role of the acid catalyst in the dehydration of an alcohol. Select one: -The acid deprotonates the hydroxyl group and then the conjugate base protonates an adjacent carbon. -One acid molecule deprotonates the hydroxyl group and then another acid molecule deprotonates an adjacent carbon. -The acid protonates the hydroxyl group and then the conjugate base deprotonates an adjacent carbon. -One acid molecule protonates the hydroxyl group and then another acid molecule protonates an adjacent carbon.

The acid protonates the hydroxyl group and then the conjugate base deprotonates an adjacent carbon. To act as a catalyst, the acid must react and then be regenerated in the reaction. Therefore, both the acid and the resulting conjugate base play a role in the mechanism. The acid starts by donating a proton to the hydroxyl group, forming a good leaving group. Then, the conjugate base removes a proton from a carbon adjacent to where the hydroxyl group was. As the conjugate base of the acid removes a proton, the acid is regenerated.

In a molecule that contains a phenolic functional group, what properly identifies the phenol?

The benzene ring directly attached with the hydroxyl group.

How can a catalyst be recognized in a mechanism?

The catalyst is used and then regenerated in a later step. Catalysts speed up reactions by changing the mechanism. Therefore, a catalyst should be in the mechanism. Catalysts can be used multiple times for the same reaction because they are regenerated during the reaction. Therefore, you can recognize a catalyst as being used early in the mechanism and then remade later in the mechanism. Catalysts can be multiple materials, including organic molecules.

Many reflux procedures involve a required length of time for the reflux to occur. When should you start timing the reflux for the procedure? Select one: -When the reflux ring stabilizes in the condenser. -When the reflux ring passes the top of the condenser. -When the sample is transferred to the flask. -When you turn on the heat under the flask.

When the reflux ring stabilizes in the condenser. The system is refluxing when vapors are constantly being created and condensed back into the flask, at the boiling point of the solvent. Therefore, a procedure requiring a reflux time requires the sample to be at the boiling point for that period of time. At the boiling point, the reflux ring has reached an equilibrium state so it should be in a stabilized position within the condenser.

Assuming all other factors are held constant, you observe that the reaction rate is constant regardless of the amount of reactant in solution. What order of reaction is this?

Zero order.