Acid-Base Chemistry

Chemistry · 11th Class (Intermediate Part 1) · BISE Lahore

70 questions

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Acid-Base Chemistry Test

10 questions · Acid-Base Chemistry × 10

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20 questions · Periodic Table and Periodic Properties × 1, Atomic Structure × 1, Chemical Bonding × 2, Stoichiometry × 1, States and Phases of Matter × 1, Chemical Energetics × 2, Reaction Kinetics × 1, Chemical Equilibrium × 1, Acid-Base Chemistry × 1, Electrochemistry × 2, Hydrocarbons × 2, Nitrogen and Sulfur × 1, Halogens × 1, Atmosphere × 1, Basic Separation Techniques × 1, Lab Safety and Practical Skills × 1

Sample questions

Showing 10 of 70 questions from this chapter. The full bank is in the chapter test below.

1
In the Bronsted-Lowry concept, an acid is a species that:
- A.donates a proton in a proton-transfer reaction (correct answer)
- B.accepts a proton in a proton-transfer reaction
- C.accepts a pair of electrons to form a coordinate covalent bond
- D.produces hydroxide ions when dissolved in water
Why: A Bronsted-Lowry acid is a proton ( $\ce{H+}$ ) donor; the species that accepts the proton is the base. Accepting an electron pair is the Lewis definition, and releasing $\ce{OH-}$ describes an Arrhenius base.
2
The species that remains when a Bronsted-Lowry acid donates a proton is called its:
- A.conjugate acid
- B.amphoteric form
- C.conjugate base (correct answer)
- D.acid-base adduct
Why: When an acid donates a proton it becomes its conjugate base, for example HCl becomes $\ce{Cl-}$ . An acid-base adduct is the product of a Lewis acid-base reaction, not of proton loss.
3
Which ion is the conjugate acid of water?
- A. $\ce{OH-(aq)}$
- B. $\ce{H3O+}$ (aq) (correct answer)
- C. $\ce{NH4+}$ (aq)
- D. $\ce{Cl-(aq)}$
Why: Water accepting a proton forms the hydronium ion $\ce{H3O+}$ , so $\ce{H3O+}$ is water's conjugate acid. $\ce{OH-}$ is the species left when water loses a proton, so it is water's conjugate base.
4
In the reaction $\ce{NH3(g) + H2O(l) <=> NH4+(aq) + OH-(aq)}$ , water acts as:
- A.a base, because it accepts a proton from $\ce{NH3}$
- B.a base, because it releases $\ce{OH-}$ ions into the solution
- C.an acid, because it accepts a proton from $\ce{NH3}$
- D.an acid, because it donates a proton to $\ce{NH3}$ (correct answer)
Why: Water loses a proton to ammonia, so it is the proton donor and therefore the acid; $\ce{NH3}$ is the base. Releasing $\ce{OH-}$ ions is only a consequence of the proton transfer, not the definition of an acid.
5
A species that can behave either as an acid or as a base, depending on the other reactant, is described as:
- A.a conjugate species
- B.a neutral species
- C.a polyprotic species
- D.an amphoteric species (correct answer)
Why: Such a species is called amphoteric; water is the common example, acting as a base towards HCl and as an acid towards $\ce{NH3}$ . Polyprotic means an acid can lose more than one proton, which is a different idea.
6
A Lewis acid is a species that:
- A.donates a proton to a base
- B.accepts a pair of electrons and forms a coordinate covalent bond (correct answer)
- C.donates a pair of electrons and forms a coordinate covalent bond
- D.releases hydroxide ions in aqueous solution
Why: The Lewis acid accepts the electron pair and the base donates it, and the two are joined by a coordinate covalent bond. Donating a proton is the Bronsted-Lowry acid definition.
7
Boron trifluoride, $\ce{BF3}$ , behaves as a good Lewis acid because:
- A.it contains highly electronegative fluorine atoms
- B.it releases $\ce{H+}$ ions when it dissolves in water
- C.its boron atom has an incomplete octet and can accept an electron pair (correct answer)
- D.its boron atom carries a lone pair that it can donate
Why: Boron has only six electrons in its valence shell in $\ce{BF3}$ , so it accepts a lone pair from a base such as $\ce{F-}$ to give $\ce{BF4-}$ . $\ce{BF3}$ has no hydrogen to release, so it cannot act as a proton donor.
8
In the reaction $\ce{BF3 + F- -> BF4^-}$ , the species $\ce{BF4}$ - is best described as:
- A.an acid-base adduct (correct answer)
- B.a conjugate base of $\ce{BF3}$
- C.a Lewis base in the reaction
- D.a conjugate acid of $\ce{F-}$
Why: The single product of a Lewis acid-base reaction, in which the base has donated a lone pair to the acid, is called the acid-base adduct. Its charge is the algebraic sum of the charges on the two reactants.
9
Two ammonia molecules each donate a lone pair to a silver ion. In this reaction the ammonia molecules are:
- A.Lewis acids and Bronsted acids
- B.Lewis bases and Bronsted bases (correct answer)
- C.Lewis bases but Bronsted acids
- D.Lewis acids but Bronsted bases
Why: Donating a lone pair makes $\ce{NH3}$ a Lewis base, and accepting a proton would make it a Bronsted base, so it is both. The silver ion is the Lewis acid because it accepts the electron pairs.
10
Which species acts as a Lewis acid but cannot act as a Bronsted-Lowry acid?
- A.HCl
- B. $\ce{H2O}$
- C. $\ce{NH3}$
- D. $\ce{AlCl3}$ (correct answer)
Why: $\ce{AlCl3}$ has no proton to donate but its aluminium atom can accept an electron pair, so it is a Lewis acid only. HCl, $\ce{H2O}$ and $\ce{NH3}$ all contain hydrogen and can take part in proton transfer.

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