acknowledge a compound as a Brønsted-Lowry acid or a Brønsted-Lowry base. Highlight the proton transfer process that defines a Brønsted-Lowry acid-base reaction.

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Because the water molecule donates a hydrogen ion come the ammonia, that is the Brønsted-Lowry acid, when the ammonia molecule—which accepts the hydrogen ion—is the Brønsted-Lowry base. Thus, ammonia acts together a basic 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, however it calls for us to recognize what really happens when HCl is dissolved in water. Recall the the hydrogen atom is a solitary proton surrounded by a single electron. To do the hydrogen ion, we eliminate the electron, leave a bare proton. Do we really have actually bare proton floating roughly in aqueous solution? No, we do not. What yes, really happens is that the H+ ion attaches itself to H2O to do H3O+, which is referred to as the hydronium ion. For most purposes, H+ and H3O+ stand for the exact same species, yet writing H3O+ instead of H+ shows that we know that there room no ceiling protons floating roughly in solution. Rather, this protons room actually attached to solvent molecules.

With this in mind, how do we specify HCl as an acid in the Brønsted-Lowry sense? think about what happens as soon as HCl is dissolved in H2O:

We can depict this process using Lewis electron dot diagrams:

Figure (PageIndex1): A neutralization reaction take away place between citric acid or acetic acid (proton donors) in lemons or vinegar and also putrescine (proton acceptor) in the meat of fish.

Pickling is a method used to maintain vegetables making use of a naturally produced acidic environment. The vegetable, such together a cucumber, is placed in a sealed seasoned submerged in a brine solution. The brine equipment favors the development of useful bacteria and also suppresses the development of harmful bacteria. The beneficial bacteria feed on starches in the cucumber and produce lactic acid as a waste product in a process called fermentation. The lactic acid at some point increases the acidity of the brine come a level the kills any harmful bacteria, which need a simple environment. Without the harmful bacteria spend the cucumbers they room able to last much much longer than if they were unprotected. A byproduct that the pickling process changes the smell of the vegetables v the acid making them taste sour.

To her Health: Brønsted-Lowry Acid-Base reactions in Pharmaceuticals

There are many interesting applications the Brønsted-Lowry acid-base reactions in the medicine industry. For example, drugs regularly need to it is in water soluble because that maximum effectiveness. However, many complicated organic compounds are not dissolve or are only slightly dissolve in water. Fortunately, those drugs the contain proton-accepting nitrogen atom (and there space a the majority of them) can be reacted through dilute hydrochloric mountain . The nitrogen atoms—acting as Brønsted-Lowry bases—accept the hydrogen ion from the acid to make an ion, i beg your pardon is normally much more soluble in water. The modified drug molecules deserve to then be isolated as chloride salts:

where RN represents part organic compound containing nitrogen. The brand (sl aq) way “slightly aqueous,” indicating that the link RN is just slightly soluble. Drugs that space modified in this means are called hydrochloride salts. Examples include the an effective painkiller codeine, i beg your pardon is commonly administered as codeine hydrochloride. Acids other than hydrochloric acid are likewise used. Hydrobromic acid, for example, provides hydrobromide salts. Dextromethorphan, one ingredient in plenty of cough medicines, is dispensed together dextromethorphan hydrobromide. The accompanying figure shows one more medication (lidocaine) as a hydrochloride salt.

Figure provided with permission indigenous Wikipedia.

Conjugate Acid-Base Pairs

According to the Bronsted-Lowry theory of acids and bases, an acid is a proton donor and also a basic is a proton acceptor. As soon as an acid has offered up a proton, the part that continues to be is called the acid"s conjugate base. This varieties is a base due to the fact that it can accept a proton (to re-form the acid). The conjugate basic of HF (first instance 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 component of the basic that remains after a base accepts a proton is called the base"s conjugate acid. This types is an acid due to the fact that it can offer up a proton (and therefore re-form the base). The conjugate mountain of fluoride ion, F- (first 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 referral so the you can figure out the strategy of identifying them. For any kind of given mountain or base, you should have the ability to give that is conjugate basic or conjugate acid. The formula of one acid"s conjugate base is created by removing a proton (H+) native the mountain formula. The formula of the base"s conjugate acid is developed by adding a proton (H+) to the formula that the base.

Table (PageIndex1). Conjugate acid-base pairs.

Conjugate mountain 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 (b) H2CO3.

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


a. NO2– is the conjugate basic of HNO2.

b. HCO3– is the conjugate basic of H2CO3

c. C6H5NH3+ is the conjugate mountain of C6H5NH2.

d. H2CO3 is the conjugate acid of HCO3–

In the reaction the ammonia v water to provide ammonium ions and hydroxide ions, ammonia acts as a base by accepting a proton indigenous a water molecule, i beg your pardon in this case means that water is acting as an acid. In the turning back 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 bag for this reaction are (NH_4^+/NH_3) and also (H_2O/OH^−). This way that the conjugate mountain of the basic NH3 is NH4+ when the conjugate base of the mountain NH4+ is NH3. Similarly, the conjugate basic of the acid H2O is OH-, and the conjugate acid of the basic OH- is H2O.


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

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When hydrogen fluoride (HF) dissolves in water and also ionizes, protons space transferred indigenous hydrogen fluoride (parent acid) molecule to water (parent base) molecules, yielding hydronium ions (conjugate acid of water) and also fluoride ion (conjugate base of HF):

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


Give the meanings of a Brønsted-Lowry acid and a Brønsted-Lowry base.