Question

Question #99f87

Answer 1

Warning! Long Answer. a) The weaker base is D. b). Its conjugate acid is B. c). The species that predominate at equilibrium are CD.

Explanation:

Step 1. Identify the conjugate acid-base pairs

In any Brønsted conjugate base pair,

• The conjugate base has one less proton than the acid.
• The conjugate acid has one more proton than the base.

`underbrace("C"_6"H"_9"O"^"-")_color(red)(bb"A":color(white)(l) "base") + underbrace("HCO"_3^"-")_color(red)(bb"B":color(white)(l) "acid") ⇌ underbrace("C"_6"H"_10"O")_color(red)(bb"C":color(white)(l) "acid") + underbrace("CO"_3^"2-")_color(red)(bb"D":color(white)(l) "base")`

Thus, cyclohexanone and cyclohexanone enolate (C and A) are one acid-base pair.

And the hydrogen carbonate and carbonate ions (B and D) are the other acid/base pair.

Step 2. Identify the stronger and weaker bases

From a table of `"p"K_text(a)` values, we get

`bb(color(white)(mmll)"Acid"color(white)(mmmll)"p"K_text(a)color(white)(m)"Strength"color(white)(mm)"Base"color(white)(mm)"p"K_text(b)color(white)(m)"Strength")`
`bb("B")color(white)(l)"HCO"_3^"-"color(white)(mmmmm)10.32color(white)(mm)"strong"color(white)(mm)bb("D")color(white)(l)"CO"_3^"2-"color(white)(mml)3.68color(white)(mmll)"weak"`
`bb("C")color(white)(l)"cyclohexanone"color(white)(m)16.7color(white)(mml)"weak"color(white)(mmll)bb("A")color(white)(l)"enolate"color(white)(m)"-2.7"color(white)(mmml)"strong"`

The `"p"K_text(b)` values come from the relationship

`"p"K_text(b) = 14.00 - "p"K_text(a)`

We see that B is a stronger acid than C and A is a stronger base than D.

Also, if A is the stronger acid, then D is the weaker base.

Step 3. Locate the position of equilibrium

Now, we can write

`underbrace("C"_6"H"_9"O"^"-")_color(red)(bb"A":color(white)(l) " stronger base") + underbrace("HCO"_3^"-")_color(red)(bb"B":color(white)(l) "stronger acid") ⇌ underbrace("C"_6"H"_10"O")_color(red)(bb"C":color(white)(l) "weaker acid") + underbrace("CO"_3^"2-")_color(red)(bb"D":color(white)(l) "weaker base")`

The stronger acid and the stronger base are both on the Left hand side, so the position of equilibrium will lie to the right (C and D).