Chemistry Acid-base Practice Problems With Answers Pdf

[Debra Necochea]

Seeif you can identify the nucleophile or base in these reactions below. When there are multiple potential nucleophiles/bases present, choose the strongest one. (More on that in a second).

Another point which often trips students up is in failing to distinguish potential nucleophiles from various aprotic solvents which find use in, but do not participate in, these reactions.

At the bottom are various polar protic solvents such as water, alcohols, carboxylic acids and even ammonia. These solvents are capable of participating in substitution/elimination reactions.

Now that we have had some practice in identifying the likely nucleophile, I am going to suggest a somewhat rough but very helpful classification that will help in distinguishing SN1/E1 reactions from SN2/E2 reactions.

The rate determining step in SN1/E1 reactions is formation of a carbocation, which is generally only possible with secondary and tertiary substrates in highly polar, ionizing solvents like water, alcohols, carboxylic acids and mixtures thereof. Carbocations have an empty p-orbital and will readily combine even with weak Lewis bases such as water and alcohols since the carbon on the resulting product will have a full octet.

The rate determining step in SN2/E2 requires that the nucleophile/base displace a leaving group from a carbon that already has a full octet. Generally these reactions work best when the nucleophile/base is a stronger base than the leaving group.

Since alcohols, water, and carboxylic acids are relatively poor bases, many SN2/E2 reactions with them as nucleophiles/bases are disfavored from an acid-base standpoint. [See article: What Makes A Good Leaving Group] [Note 3]

For secondary alkyl halides with weakly basic nucleophiles, expect SN2 for everything up to thiolates, and elimination for everything more basic than alkoxides. Amide bases (e.g. NH2(-), R2N(-), NaH, and acetylides will primarily give E2 products. (Acetylides are fine nucleophiles with primary alkyl halides, but will perform E2 reactions on secondary alkyl halides).

Primary alkyl halide + aq. KOH , product is decided by SN2 or E2 ?my teacher told it follow SN2 but according to quick and dirty method it will go for E2 ( as water is polar protic solvent ).Sir please tell the answer.I am very confused ?

Your textbook actually does a better job of describing reality than most textbooks do. In reality the SN2 is pretty tough for secondary alkyl halides/ tosylates. May I ask what textbook you are using?

Hi!!

I had a chem problem, so the original reaction is 1-bromopentane with NaOH which would undergo the SN2 reaction, however what experimental modifications can be done in order to form 1-pentene (E2 product). I already said a hindered base could be used like NaOC(CH3)3 however i need one more experimental modifcation, would heat work? Just by adding head to 1-bromopentane would that favour the E2 reaction rather than the SN2 reaction?

You can think it this way: the carbon in an alkyl halide before SN1 is sp3 hybridised. Thus, it has tetrahedral Geometry. But after formation of carbocation, the carbon is sp2 hybridised and has planar geometry, hence , greater stability.

P(Ph)3 is a weak base because the lone pair on Phospohorous is involved in resonance with the three phenyl groups and hence the lone pair is less available for donation .This would decrease its ability to act as a base (Lewis base concept).Firstly is this correct?

And since P(Ph)3 is a weak base it favours Sn2 over E2 even though its bulky.Right?

Generally speaking, yes. And yes, they are typically always written in this manner. A lot of the time, you will also see reaction conditions (like temperature and rxn time) written underneath the arrow as well.

It means that OH-(conjugate base) is a stronger nucleophile than H20(acid). Whenever we form conjugate bases we get a negatively charged species. As negatively charged species is a better nucleophile we can call conjugate base as stronger nucleophile

You should to able to find good reference tables with pKa values calculated and already listed for organic compounds and the like, either online or in a major chemistry textbook (especially o-chem textbooks), if you need to look up values! Hope this helps!

Hey.Great site-I can understand and enjoy organic chem better now.

A Question.How can triphenyl phosphine be a good nucleophile ?? It has three phenyl rings then it should be sterically hindered.

First of all the PPh3 has a trigonal pyramidal geometry, so a lone pair is pointing in the opposite direction from the phenyl groups. Secondly, the C-P bonds are fairly long which decreases the steric hindrance somewhat. PPh3 is a good enough nucleophile to do SN2 reactions of primary and secondary alkyl halides.

in the exception column PPh3 undergoes SN2 but P is stabilized by 3 Ph and therefore will undergo Sn1 right?or is e- density on P high as it is not electronegative(unlike F) even after resonance stabilization?

CH3OH is acidic than water and for that matter any alcohol ROH is in equilibrium with RO- and H+,so wont RO- attack as a good nucleophile ?I know it is a weird question yet still how do we explain it will only ROH attacking always and not RO-.Pls reply ASAP

Hi, what if you have a strong nucleophile and a strong base like OH- and you are reacting with a tertiary haloalkane. Does not Sn1 and E2 pathway is both possible? How would you then choose whether Sn1 work? Assume there is no solvent. Thanks!

E2 takes place as Oh- is a good nucleophile ie unstable so whatever comes into its hand it will take it moreover in Sn1 it needs to penetrate the steric hindrances provided therefore E2 is preferred.E2 doesnt need a polar aprotic solvent(we just say like that)

Definition of acids and bases, identifying them along with the conjugate acid and conjugate base, pH of strong and weak acids and bases, the pH and pOH relationship, Ka and Kb, pKa and Ka correlation, the acid-base properties of salts, identifying the acidity of the salt based on the acid and the base it is prepared from, and calculating the pH of salt solutions. This is what is covered in this summary practice problem set on acids and bases.

Morphine is among the most popular alkaloids that are used as pain killers. Like all the others, it contains a nitrogen atom which makes it a weak base. What is the Kb of morphine at a certain temperature if its 0.340 M solution has a pH of 10.9?

Full discussions of the topics covered by these problems are available in the Virtual Textbook of Organic Chemistry.

The following button will activate a random display of problems concerning the reactivity of common functional groups.

A large collection of multiple choice problems, similar to those used in standardized examinations, may be reached by clicking here

Most of these Interactive Organic Chemistry Practice Problems have been developed by Professor WilliamReusch.

1999 William Reusch, All rights reserved. Comments, questions and errors shouldbe sent to whre...@msu.edu.

The Virtual Text and some of the problems make use of either the CHIME plugin, or Jmol. Click on the name for information and a free copy.

If possible, monitor resolutions of 1024 x 768 or 1152 x 870 should be used.

The practice problems offered here are chiefly interactive, and should provide a useful assessment of understanding at various stages in the development of the subject.

Since problem solving is essential to achieving an effective mastery of the subject, it is recommended that many more problems be worked. Most organic chemistry textbooks contain a broad assortment of suitable problems, and paperback collections of practice problems are also available.

The following web-sites provide nice collections of problems and answers: MIT Open CourseWare

Reaction quizzes and summaries from Towson University

Electronic flashcards from Ohio State University

Concept questions from University of Wisconsin

Practice problems from UCLA

Arrow Pushing Tutorial

BestChoice, University of Auckland Demo may be used

Spectroscopy problems from Notre Dame

The major component of the solution is called solvent, and the minor component(s) are called solute. If both components in a solution are 50%, the term solute can be assigned to either component. When a gaseous or solid material dissolves in a liquid, the gas or solid material is called the solute. When two liquids dissolve in each other, the major component is called the solvent and the minor component is called the solute.

Many chemical reactions are carried out in solutions, and solutions are also closely related to our everyday lives. The air we breathe, the liquids we drink, and the fluids in our body are all solutions. Furthermore, we are surrounded by solutions such as the air and waters (in rivers, lakes and oceans).

The maximum amount of a substance that can be dissolved in a given volume of solvent is called solubility. Often, the solubility in water is expressed in gram/100 mL. A solution that has not reached its maximum solubility is called an unsaturated solution. This means that more solute could still be added to the solvent and dissolving would still occur.

A solution that has reached the maximum solubility is called a saturated solution. If more solute is added at this point, it will not dissolve into the solution. Instead it will remain precipitated as a solid at the bottom of the solution. Thus, one can often tell that a solution is saturated if extra solute is present (this can exist as another phase, such as gas, liquid, or solid). In a saturated solution there is no net change in the amount of solute dissolved, but the system is by no means static. In fact, the solute is constantly being dissolved and deposited at an equal rate. Such a phenomenon is called equilibrium. For example:

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