Recognize a compound as a Brønsted-Lowry acid or a Brønsted-Lowry base. Illustrate the proton carry process that specifies a Brønsted-Lowry acid-base reaction.

You are watching: Which of the following describes a brønsted–lowry acid?


Due to the fact that the water molecule donates a hydrogen ion to the ammonia, it is the Brønsted-Lowry acid, while the ammonia molecule—which accepts the hydrogen ion—is the Brønsted-Lowry base. Hence, ammonia acts as a base in both the Arrhenius sense and also the Brønsted-Lowry sense.

Is an Arrhenius acid choose hydrochloric acid still an acid in the Brønsted-Lowry sense? Yes, yet it needs us to understand what really happens once HCl is dissolved in water. Respeak to that the hydrogen atom is a single proton surrounded by a solitary electron. To make the hydrogen ion, we rerelocate the electron, leaving a bare proton. Do we really have bare protons floating about in aqueous solution? No, we perform not. What really happens is that the H+ ion attaches itself to H2O to make H3O+, which is dubbed the hydronium ion. For the majority of purposes, H+ and also H3O+ recurrent the very same species, but composing H3O+ rather of H+ reflects that we understand that tright here are no bare proloads floating about in solution. Rather, these protons are actually attached to solvent molecules.

With this in mind, exactly how do we define HCl as an acid in the Brønsted-Lowry sense? Consider what happens when HCl is liquified in H2O:

We deserve to depict this process using Lewis electron dot diagrams:


Pickling is a method offered to keep vegetables making use of a naturally created acidic environment. The vegetable, such as a cucumber, is put in a sealed jar subunified in a brine solution. The brine solution favors the growth of helpful bacteria and suppresses the growth of harmful bacteria. The helpful bacteria feed on starcs in the cucumber and also produce lactic acid as a waste product in a procedure referred to as fermentation. The lactic acid inevitably increases the acidity of the brine to a level that kills any harmful bacteria, which need a simple setting. Without the harmful bacteria consuming the cucumbers they are able to last a lot longer than if they were unprotected. A byproduct of the pickling procedure alters the flavor of the vegetables with the acid making them taste sour.

To Your Health: Brønsted-Lowry Acid-Base Reactions in Pharmaceuticals

Tbelow are many amazing applications of Brønsted-Lowry acid-base reactions in the pharmaceutical industry. For instance, drugs frequently need to be water soluble for maximum efficiency. However, many kind of facility organic compounds are not soluble or are only slightly soluble in water. Fortunately, those drugs that contain proton-accepting nitrogen atoms (and also tbelow are the majority of them) can be reacted through dilute hydrochloric acid . The nitrogen atoms—acting as Brønsted-Lowry bases—accept the hydrogen ions from the acid to make an ion, which is normally much more soluble in water. The modified drug molecules deserve to then be isolated as chloride salts:

wright here RN represents some organic compound containing nitrogen. The label (sl aq) implies “slightly aqueous,” indicating that the compound RN is only slightly soluble. Drugs that are modified in this way are dubbed hydrochloride salts. Examples incorporate the powerful painkiller codeine, which is frequently administered as codeine hydrochloride. Acids other than hydrochloric acid are additionally offered. Hydrobromic acid, for example, provides hydrobromide salts. Dextromethorphan, an ingredient in many kind of cough drugs, is dispensed as dextromethorphan hydrobromide. The accompanying figure reflects another medication (lidocaine) as a hydrochloride salt.

Figure supplied via permission from Wikipedia.

Conjugate Acid-Base Pairs

According to the Bronsted-Lowry theory of acids and bases, an acid is a proton donor and also a base is a proton acceptor. Once an acid has given up a proton, the component that stays is referred to as the acid"s conjugate base. This species is a base because it have the right to accept a proton (to re-create the acid). The conjugate base of HF (initially example below) is fluoride ion, F-.

(mathrmcolorRed Acid = H^+ + colorBlue Conjugate: base: of: Acid^-)

(colorRed mathrmHF ightleftharpoons mathrmH^+ + colorBlue mathrmF^-)

(colorRed mathrmH_2O ightleftharpoons mathrmH^+ + colorBlue mathrmOH^-)

(colorRed mathrmNH_4^+ ightleftharpoons mathrmH^+ + colorBlue mathrmNH_3)

Similarly, the part of the base that remains after a base accepts a proton is referred to as the base"s conjugate acid. This species is an acid because it can provide up a proton (and for this reason re-form the base). The conjugate acid of fluoride ion, F- (initially example below) is HF.

(mathrmH^+ + colorBlue Base = colorRed Conjugate: acid: of: Base^+)

(mathrmH^+ + colorBlue F^- ightleftharpoons colorRed HF)

(mathrmH^+ + colorBlue OH^- ightleftharpoons colorRed H_2O)

(mathrmH^+ + colorBlue H_2O ightleftharpoons colorRed H_3O^+)

(mathrmH^+ + colorBlue NH_3 ightleftharpoons colorRed NH_4^+)

To summarize, the conjugate base of HF is fluoride ion, F-, and also the conjugate acid of fluoride ion, F-, is HF. The HF/F- pair is described as a conjugate acid-base pair. The difference in the formulas of a conjugate acid-base pair (example: HF and F-) is H+. The table below lists conjugate acid-base pairs for your reference so that you deserve to number out the strategy of identifying them. For any given acid or base, you should be able to give its conjugate base or conjugate acid. The formula of an acid"s conjugate base is generated by removing a proton (H+) from the acid formula. The formula of the base"s conjugate acid is developed by adding a proton (H+) to the formula of the base.

Table (PageIndex1). Conjugate acid-base pairs.

Conjugate Acid Conjugate Base
(ceH3O+) (ceH2O)
(ceH2O) (ceOH-)
(ceH2SO4) (ceHSO4-)
(ceHSO4-) (ceSO4^2-)
(ceNH4+) (ceNH3)
(ceNH3) (ceNH2-)
(ceCH3COOH) (ceCH3COO-)
(ceCH3NH3+) (ceCH3NH2)

Exercise (PageIndex3): Conjugate Pairs

Write the formula of the conjugate base of (a) HNO2 and also (b) H2CO3.

Write the formula of the conjugate acid of (c) C6H5NH2 and (d) HCO3–.


a. NO2– is the conjugate base of HNO2.

b. HCO3– is the conjugate base of H2CO3

c. C6H5NH3+ is the conjugate acid of C6H5NH2.

d. H2CO3 is the conjugate acid of HCO3–

In the reaction of ammonia through water to give ammonium ions and also hydroxide ions, ammonia acts as a base by accepting a proton from a water molecule, which in this instance means that water is acting as an acid. In the reverse reaction, an ammonium ion acts as an acid by donating a proton to a hydroxide ion, and the hydroxide ion acts as a base. The conjugate acid–base pairs for this reactivity are (NH_4^+/NH_3) and also (H_2O/OH^−). This suggests that the conjugate acid of the base NH3 is NH4+ while the conjugate base of the acid NH4+ is NH3. Similarly, the conjugate base of the acid H2O is OH-, and also the conjugate acid of the base OH- is H2O.


In the forward reaction, the parent acid is H2O and and also the parent base is NH3 (shown in the illustration below). The acid H2O loses a proton (H+) to develop its conjugate base OH-. The base NH3 gains a proton, to develop its conjugate acid NH4+. In the reverse reactivity, the acid NH4+ loses a proton (H+) to form its conjugate base NH3. The base OH- gains a proton, to develop its conjugate acid H2O.

See more: Is Hydrogen A Good Conductor Of Electricity, Metallic Hydrogen


When hydrogen fluoride (HF) dissolves in water and also ionizes, prolots are transferred from hydrogen fluoride (parent acid) molecules to water (parent base) molecules, yielding hydronium ions (conjugate acid of water) and fluoride ions (conjugate base of HF):

(colorRed mathrmHF + colorBlue H_2O ightleftharpoons colorBlue H_3O^+ + colorRed mathrmF^-)


Give the interpretations of a Brønsted-Lowry acid and also a Brønsted-Lowry base.