Acids and Bases: Quiz

Acids and Bases: Quiz

7 questions

1. Question 1EasyAccording to the Brønsted–Lowry definition, an acid is a substance that…

   Aaccepts a protonBdonates a protonCaccepts an electron pairDproduces hydroxide ions
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   Answer: donates a proton

   A Brønsted–Lowry acid donates a proton ($\ce{H+}$) and a base accepts one. Accepting an electron pair is the Lewis definition of an acid; producing $\ce{OH-}$ describes an Arrhenius base.

2. Question 2EasyIn $\ce{HCl + H2O -> H3O+ + Cl-}$, which substance acts as the base?

   A$\ce{HCl}$B$\ce{H2O}$C$\ce{H3O+}$D$\ce{Cl-}$
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   Answer: $\ce{H2O}$

   Water accepts the proton from $\ce{HCl}$ and becomes $\ce{H3O+}$, so water is the base here.

3. Question 3MediumWhat is the conjugate acid of $\ce{NH3}$?

   A$\ce{NH2-}$B$\ce{NH4+}$C$\ce{H3O+}$D$\ce{OH-}$
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   Answer: $\ce{NH4+}$

   A conjugate acid has one more $\ce{H+}$ than its base: $\ce{NH3}$ + $\ce{H+}$ → $\ce{NH4+}$. $\ce{NH2-}$ is the conjugate base of $\ce{NH3}$.

4. Question 4MediumWhich pair is a conjugate acid–base pair?

   A$\ce{H3O+}$ and $\ce{OH-}$B$\ce{HNO3}$ and $\ce{NO3-}$C$\ce{HCl}$ and $\ce{NaOH}$D$\ce{NH4+}$ and $\ce{NH2-}$
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   Answer: $\ce{HNO3}$ and $\ce{NO3-}$

   A conjugate pair differs by exactly one $\ce{H+}$. $\ce{HNO3}$ and $\ce{NO3-}$ do. $\ce{H3O+}$/$\ce{OH-}$ and $\ce{NH4+}$/$\ce{NH2-}$ differ by two protons.

5. Question 5EasyWhat does it mean to say that acetic acid is a weak acid?

   AIts solutions are always diluteBIt ionizes only partly in waterCIt cannot react with basesDIt contains no hydrogen
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   Answer: It ionizes only partly in water

   Weak refers to how much the acid ionizes, not how much is dissolved. Weak acids still react with bases; a concentrated solution of a weak acid is possible.

6. Question 6EasyWhat are the products when nitric acid, $\ce{HNO3}$, is neutralized by potassium hydroxide, $\ce{KOH}$?

   A$\ce{KNO3 + H2O}$B$\ce{KH + HNO3}$C$\ce{K + NO3 + H2O}$D$\ce{KOH + H2}$
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   Answer: $\ce{KNO3 + H2O}$

   Acid + base → salt + water. The salt combines $\ce{K+}$ from the base with $\ce{NO3-}$ from the acid: $\ce{HNO3 + KOH -> KNO3 + H2O}$.

7. Question 7HardIn $\ce{NH3 + H2O <=> NH4+ + OH-}$, what role does water play?

   AAcidBBaseCSaltDIt takes no part in the reaction
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   Answer: Acid

   Water donates a proton to ammonia and becomes $\ce{OH-}$, so it acts as an acid. With HCl, water acts as a base, which is why water is called amphoteric.