According come Brønsted and also Lowry an acid is a proton donor and also a base is a proton acceptor. This idea that proton donor and also proton acceptor is important in expertise monoprotic and also polyprotic acids and bases due to the fact that monoprotic coincides to the carry of one proton and also polyprotic describes the transfer of more than one proton. Therefore, a monoprotic acid is an mountain that have the right to donate only one proton, if polyprotic acid can donate more 보다 one proton. Similarly, a monoprotic base have the right to only accept one proton, when a polyprotic base deserve to accept more than one proton.

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Introduction

One means to display the differences between monoprotic and polyprotic acids and bases is with titration, which plainly depicts the equivalence points and acid or basic dissociation constants. The mountain dissociation constant, signified by \(K_a\), and the basic dissociation constant, \(K_b\), room equilibrium constants for the dissociation that weak acids and weak bases. The bigger the worth of either \(K_a\) or \(K_b\) signifies a stronger acid or base, respectively.

Here is a perform of essential equations and constants when managing \(K_a\) and also \(K_b\):

For the general equation of a weak acid,

\

you must solve because that the \(K_a\) value. To carry out that friend use

\ \label2\>

Another essential value is the \(pK_a\) value, and also that is acquired through \(pK_a = -logK_a\)

The procedure is very comparable for weak bases. The basic equation of a weak base is

\

Solving for the \(K_b\)value is the very same as the \(K_a\) value. You usage the formula

\ \label4\>

The \(pK_b\) worth is uncovered through \(pK_b = -logK_b\)

The \(K_w\) worth is discovered with\(K_w = \).

\


Monoprotic Acids

Monoprotic acids room acids that deserve to release only one proton every molecule and have one equivalence point.

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Here is a perform of some common polyprotic acids:

name Formula \(\pmbK_a1\) \(\pmbK_a2\) \(\pmbK_a3\)
Sulfuric acid (strong, diprotic) H2SO4 1.0 x 103 1.2 x 10-2 -
Carbonic mountain (weak, diprotic) H2CO3 4.2 x 10-7 4.8 x 10-11 -
Phosphoric mountain (weak, triprotic) H3PO4 7.1 x 10-3 6.3 x 10-8 4.2 x 10-13


Example \(\PageIndex2\)

For a 4.0 M H3PO4 solution, calculate (a) (b) and also (c) .

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Solution

(a) utilizing ICE Tables you get:

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So,

\(x^2\) = .0284

\(x\) = 0.17 M

(b) From part (a), \(x\) = = = 0.17 M

(c) To recognize and also , it was assumed the the 2nd ionization constant was insignificant.

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The new equation is together follows:

\(H_2PO_4^- + H_2O \Longleftrightarrow H_3O^+ + HPO_4^2-\)

Using ice Tables again:

\(K_a2 = = 6.3 \times 10^-8\)



Summary

Ka and also Kb space equilibrium constants and also a high worth signifies a stronger acid or base. Acid space proton donors and bases room proton acceptors. Monoprotic acid/base corresponds to the donation/acceptance that only one proton. Polyprotic acid/base synchronizes to the donation/acceptance of more 보다 one proton. remember diprotic and triprotic. \(K_a1\)>\(K_a2\)>\(K_a3\)

Common Errors

Assuming that the is the very same for all the ionizations. In fact, the pH is overcame by only the an initial ionization, yet the later ionizations carry out contribute really slightly.

References

Petrucci, et al. General sdrta.netistry: values & contemporary Applications. Ninth ed. Top Saddle River, new Jersey: Pearson/Prentice Hall, 2007. Sadava, et al. Life: The science of Biology. 8 hours ed. Brand-new York, NY. W.H. Freeman and Company, 2007 Hulanicki, Adam. Reaction of Acids and Bases In analysis sdrta.netistry. New York, NY: Ellis Horowood Limited, 1987.