Strong Acids

In water, solid acids totally dissociate into complimentary proloads and also their conjugate base.

You are watching: If hydrofluoric acid is a stronger acid than acetic acid, which statement is most likely true?


Key Takeaways

Key PointsStrong acids can catalyze chemical reactions.Strong acids are identified by their pKa. The acid have to be more powerful in aqueous solution than a hydronium ion, so its pKa have to be lower than that of a hydronium ion. Therefore, strong acids have a pKa of Strong acids deserve to be organic or inorganic.Strong acids have to be tackled carefully bereason they have the right to cause significant chemical burns.Strong acids are important for catalyzing some reactions, including the synthesis and also hydrolysis of carbonyl compounds.Key Termscarbonyl: a divalent functional group (-CO-), characteristic of aldehydes, ketones, carboxylic acids, amides, carboxylic acid anhydrides, carbonyl halides, esters, and also others.ester: a compound commonly formed by condensing an alcohol and an acid and also eliminating of water. it contains the useful group carbon-oxygen double bond joined by means of carbon to one more oxygen atomhydrolysis: a chemical procedure of decomposition; entails dividing a bond and also adding the hydrogen cation and water’s hydroxide anion

Definition of Strong Acids

The toughness of an acid describes the ease with which the acid loses a proton. A solid acid ionizes completely in an aqueous solution by shedding one proton, according to the following equation:

extHA ( extaq) ightarrow extH^+ ( extaq) + extA^-( extaq)

wbelow HA is a protonated acid, H+ is the complimentary acidic proton, and also A– is the conjugate base. Strong acids yield weak conjugate bases. For sulfuric acid, which is diprotic, the “solid acid” desigcountry refers just to the dissociation of the first proton:

extH_2 extSO_4 ( extaq) ightarrow extH^+ ( extaq) + extHSO_4 ^- ( extaq)

More specifically, the acid need to be more powerful in aqueous solution than a hydronium ion (H+), so solid acids have actually a pKa

Ionization of acids and bases in water: A strong acid ionizes completely in an aqueous solution by shedding one proton (H+).


Due to the complete dissociation of solid acids in aqueous solution, the concentration of hydronium ions in the water is equal to the full concentration (ionized and un-ionized) of the acid presented to solution:

= = complete and also pH = −log.

Strong acids, like strong bases, deserve to cause chemical burns as soon as exposed to living tconcern.

Instances of Strong Acids

Some widespread solid acids (acids through pKa Hydroiodic acid (HI): pKa = -9.3Hydrobromic acid (HBr): pKa = -8.7Perchloric acid (HClO4): pKa ≈ -8Hydrochloric acid (HCl): pKa = -6.3Sulfuric acid (H2SO4): pKa1 ≈ -3 (first dissociation only)p-Toluenesulfonic acid: pKa = -2.8Nitric acid (HNO3): pKa ≈ -1.4Chloric acid (HClO3): pKa ≈ 1.0

p-Toluenesolfonic acid: p-Toluenesulfonic acid is an example of an organic soluble solid acid, via a pKa of -2.8.


Strong Acid Catalysis

Strong acids have the right to accelerate the price of particular reactions. For instance, solid acids deserve to acceleprice the synthesis and also hydrolysis of carbonyl compounds. With carbonyl compounds such as esters, synthesis and also hydrolysis go through a tetrahedral transition state, wbelow the central carbon has an oxygen, an alcohol team, and the original alkyl team. Strong acids protonate the carbonyl, which provides the oxygen positively charged so that it have the right to easily get the double-bond electrons once the alcohol strikes the carbonyl carbon; this enables ester synthesis and also hydrolysis.


Weak Acids

A weak acid just partly dissociates in solution.



Key Takeaways

Key PointsThe dissociation of weak acids, which are the many renowned type of acid, have the right to be calculated mathematically and used in experimental job-related.If the concentration and also Ka of a weak acid are well-known, the pH of the whole solution can be calculated. The precise technique of calculation varies according to what assumptions and also simplifications have the right to be made.Weak acids and weak bases are vital for preparing buffer solutions, which have important experimental uses.Key Termsconjugate acid: the species produced when a base accepts a protonconjugate base: the species developed after donating a proton.weak acid: one that dissociates incompletely, donating only some of its hydrogen ions right into solution

Vinegars: All vinegars contain acetic acid, a prevalent weak acid.


Dissociation

Weak acids ionize in a water solution only to a really moderate level. The generalized dissociation reactivity is given by:

extHA( extaq) ightleftharpoons extH^+ ( extaq) + extA^- ( extaq)

wbelow HA is the undissociated species and also A– is the conjugate base of the acid. The strength of a weak acid is stood for as either an equilibrium continuous or a percent dissociation. The equilibrium concentrations of reactants and also assets are related by the acid dissociation continuous expression, Ka:

extK_ exta = frac< extH^+>< extA^->< extHA>

The higher the value of Ka, the even more favored the H+ formation, which makes the solution more acidic; therefore, a high Ka value indicates a reduced pH for a solution. The Ka of weak acids varies in between 1.8×10−16 and also 55.5. Acids via a Ka less than 1.8×10−16 are weaker acids than water.

If acids are polyprotic, each proton will have a unique Ka. For example, H2CO3 has two Ka values bereason it has actually 2 acidic prolots. The initially Ka describes the initially dissociation step:

extH_2 extCO_3 + extH_2 extO ightarrowhead extHCO_3^- + extH_3 extO^+

This Ka worth is 4.46×10−7 (pKa1 = 6.351). The second Ka is 4.69×10−11 (pKa2 = 10.329) and also describes the second dissociation step:

extHCO_3^- + extH_2 extO ightarrowhead extCO_3^2- + extH_3 extO^+

Calculating the pH of a Weak Acid Solution

The Ka of acetic acid is 1.8 imes 10^-5. What is the pH of a solution of 1 M acetic acid?

In this case, you can uncover the pH by resolving for concentration of H+ (x) using the acid’s concentration (F) and Ka. Assume that the concentration of H+ in this straightforward case is equal to the concentration of A–, given that the two dissociate in a 1:1 mole ratio:

extK_ exta = frac< extH^+>< extC_2 extH_3 extO_2^->< extHA> = frac extx^2( extF- extx)

This quadratic equation have the right to be manipulated and addressed. A prevalent assumption is that x is small; we can justify assuming this for calculations involving weak acids and bases, because we recognize that these compounds only dissociate to a really little extent. Because of this, our over equation simplifies to:

extK_ exta=1.8 imes 10^-5=frac extx^2 extF- extxapprox frac extx^2 extF=frac extx^21 ext M

1.8 imes 10^-5= extx^2

extx=3.9 imes 10^-3 ext M

extpH=- extlog< extH^+>=- extlog(3.9 imes 10^-3)=2.4

Although it is only a weak acid, a focused enough solution of acetic acid deserve to still be fairly acidic.


Calculating Percent Dissociation

Percent dissociation represents an acid’s strength and also have the right to be calculated making use of the Ka worth and also the solution’s pH.

See more: What Is The Difference Between Endoparasites And Ectoparasites And Endoparasites



Key Takeaways

Key PointsPercent dissociation is symbolized as α ( alpha ) and represents the ratio of the concentration of dissociated hydrogen ion to the concentration of the undissociated species .Unchoose Ka, percent dissociation varies through the concentration of HA; dilute acids dissociate more than focused ones.Percent dissociation is related to the concentration of both the conjugate base and also the acid ‘s initial concentration; it deserve to be calculated if the pH of the solution and also the pKa of the acid are known.Key Termsdissociation: the procedure by which compounds break-up into smaller constituent molecules, commonly reversibly.percent ionization: the fraction of an acid that undergoes dissociation