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💏intro to chemistry review

NH₃

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

NH₃, also known as ammonia, is a chemical compound composed of one nitrogen atom and three hydrogen atoms. It is a colorless gas with a pungent odor and is an important compound in the context of Brønsted-Lowry acid-base theory.

5 Must Know Facts For Your Next Test

  1. NH₃ is a Brønsted-Lowry base, as it can accept a proton (H⁺) to form the conjugate acid, NH₄⁺ (ammonium ion).
  2. The reaction between NH₃ and H₂O (water) is an example of a Brønsted-Lowry acid-base reaction, where NH₃ acts as a base and H₂O acts as an acid.
  3. The conjugate acid-base pair of NH₃ and NH₄⁺ is an important concept in Brønsted-Lowry acid-base theory, as it demonstrates the relationship between an acid and its corresponding base.
  4. NH₃ is a weak base, meaning it only partially dissociates in water, producing a relatively low concentration of hydroxide ions (OH⁻) compared to a strong base.
  5. The pH of a solution containing NH₃ and NH₄⁺ is determined by the relative concentrations of these species, as well as the equilibrium constant (Ka) for the dissociation of NH₄⁺.

Review Questions

  • Explain how NH₃ can act as a Brønsted-Lowry base and describe the reaction with water to form the conjugate acid, NH₄⁺.
    • NH₃ is a Brønsted-Lowry base because it can accept a proton (H⁺) from another substance, such as water (H₂O). When NH₃ reacts with water, it accepts a proton from the water molecule, forming the conjugate acid, NH₄⁺ (ammonium ion). This reaction can be represented as: NH₃ + H₂O ⇌ NH₄⁺ + OH⁻. The NH₃/NH₄⁺ pair is an example of a conjugate acid-base pair, where NH₃ is the base and NH₄⁺ is the corresponding acid.
  • Describe the role of NH₃ in the context of Brønsted-Lowry acid-base theory and explain how it relates to the concept of pH.
    • In the context of Brønsted-Lowry acid-base theory, NH₃ is considered a weak base, meaning it only partially dissociates in water to produce a relatively low concentration of hydroxide ions (OH⁻). The pH of a solution containing NH₃ and its conjugate acid, NH₄⁺, is determined by the relative concentrations of these species, as well as the equilibrium constant (Ka) for the dissociation of NH₄⁺. The presence of NH₃ in a solution can increase the pH, as it acts as a proton acceptor, thereby increasing the concentration of hydroxide ions and making the solution more basic.
  • Analyze the relationship between NH₃ and NH₄⁺ as a conjugate acid-base pair, and explain how this relationship is important in understanding Brønsted-Lowry acid-base theory.
    • The relationship between NH₃ and NH₄⁺ as a conjugate acid-base pair is a fundamental concept in Brønsted-Lowry acid-base theory. NH₃ acts as a base, accepting a proton (H⁺) to form the conjugate acid, NH₄⁺. Conversely, NH₄⁺ can act as an acid, donating a proton to form the conjugate base, NH₃. This interconversion between the acid and base forms is crucial for understanding how Brønsted-Lowry acids and bases behave in aqueous solutions and how they influence the pH of the solution. The equilibrium between NH₃ and NH₄⁺ is an important factor in determining the pH of a solution, as it directly affects the concentration of hydroxide ions (OH⁻) and hydrogen ions (H⁺).

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