Problem 88 - Chemistry: An Atoms-Focused Approach

Question

Are all Arrhenius acids also Bronsted-Lowry acids? Are all Bronsted-Lowry acids also Arrhenius acids? If yes, explain why. If not, give a specific example to demonstrate the difference.

Step-by-Step Solution

Answer

Answer: All Arrhenius acids are also Bronsted-Lowry acids, but not all Bronsted-Lowry acids are Arrhenius acids. The difference is that Arrhenius acids dissociate in water to produce H+ ions, while Bronsted-Lowry acids can donate protons in reactions not involving water.

Step 1: Defining Arrhenius and Bronsted-Lowry acids

An Arrhenius acid is a substance that dissociates in water to produce hydrogen ions (H+), also referred to as protons. In other words, an Arrhenius acid increases the concentration of H+ ions in the aqueous solution. A Bronsted-Lowry acid, on the other hand, is a substance that donates a proton (H+) to another substance, called a base. In this definition, a base is a proton acceptor.

Step 2: Comparing Arrhenius acids to Bronsted-Lowry acids

When we compare the definitions, we can see that all Arrhenius acids are also Bronsted-Lowry acids because they dissociate in water to produce H+ ions, meaning they act as proton donors. However, not all Bronsted-Lowry acids are Arrhenius acids because they do not necessarily need to be in an aqueous solution to donate protons.

Step 3: Providing a specific example

To illustrate the difference between these two types of acids, let's consider the reaction of hydrogen chloride (HCl) with water and with ammonia (NH3). In the reaction with water: HCl (aq) + H2O (l) ⟶ H3O+ (aq) + Cl- (aq) HCl is an Arrhenius acid because it dissociates in water to produce H+ ions. It is also a Bronsted-Lowry acid because it donates a proton to water (H2O) which acts as a proton acceptor. In the reaction with ammonia: HCl (g) + NH3 (g) ⟶ NH4+ (g) + Cl- (g) HCl acts as a Bronsted-Lowry acid, as it donates a proton to ammonia (NH3), which acts as a proton acceptor. However, this reaction does not involve water, so HCl does not act as an Arrhenius acid.

Step 4: Conclusion

In conclusion, all Arrhenius acids are also Bronsted-Lowry acids, but not all Bronsted-Lowry acids are Arrhenius acids. The difference between these two types of acids lies in the fact that Arrhenius acids dissociate in water to produce H+ ions, whereas Bronsted-Lowry acids can donate protons in reactions not involving water, as demonstrated in the HCl and NH3 reaction example.