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Chapter 2: Q18P (page 119)

Which is a stronger base: cyanide ion or fluoride ion? Give pKb values (without looking them up) to support your choice.

Short Answer

Expert verified

The stronger base is the cyanide ion.

pKb(CN-) = 4.69

pKb(F-) = 10.80

Step by step solution

01

The Acids and Bases.

Acid-base reactions are very quick. They react as soon as they are added to each other in a container. Here, acids release proton that is accepted by bases.

02

The pKb values and basicity.

The lower the value, and the higher the value, the stronger the basicity.

03

The stronger base.

A strong acid contains a weak conjugate base and weak acid carries a strong conjugate base.

The same thing goes for bases.

Out of the given ions; the cyanide ion is a stronger base because its conjugate acid is weaker than the latter.

Acids;

pKa(HCN) = 9.31

pKa(HF) = 3.20

HF is the stronger acid.

Bases:

pKb(CN-) = 4.69

pKb(F-) = 10.80

CN-ion is the stronger base.

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Most popular questions from this chapter

Each of these compounds can react as a nucleophile. In each case, use curved arrows to show how the nucleophile would react with the strong electrophile, BF3.

(a)

(b)

(c)

(d)

(CH3)3H

(e)

CH3CH2OH

(f)

(CH3 )2S

Like nitrogen and carbon, oxygen also shows this same hybridization effect on acidity. Both of the following compounds can lose a proton from a positively charged oxygen with three bonds to give a conjugate base containing a neutral oxygen with two bonds. One of these structures has pKa = -2.4 , while the other has pKa = -8.0.

  1. Show the reaction of each compound with water.
  2. Match each structure with its pKa , and explain your choice.

TheC=Odouble bond has a dipole moment of about 2.4Dand a bond length of about 1.23 Å.

  1. Calculate the amount of charge separation in this bond.
  2. Use this information to evaluate the relative importance of the following two resonance contributors:

(R is a general symbol for a carbon-containing group)

Draw a Lewis structure, and classify each of the following compounds. The possible classification are as follows:

alcohol, ketone, carboxylic acid, ether, aldehyde and alkene.

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

(i)

Consider the following compounds that vary from nearly nonacidic to strongly acidic. Draw the conjugate bases of these compounds and explain why the acidity increases so dramatically with substitution by nitro groups.
See all solutions

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