Question 39 Answer and Explanation _ACT June 2021 Form D06 Science Section

Passage VI

Each of 3 scientists provided a model of acids and bases.

Scientist 1

An acid is an uncharged substance that dissociates (breaks apart into 2 or more ions) when dissolved in H₂O, producing 1 or more hydrogen ions (H⁺) and a corresponding negative ion. A base is an uncharged substance that dissociates when dissolved in H₂O, producing a metal ion and 1 or more hydroxide ions (OH^-).

An example of an acid is hydrochloric acid (HCl) because, in H₂O, it dissociates into H⁺ and a chloride ion (Cl^-). An example of a base is sodium hydroxide (NaOH) because, in H₂O, it dissociates into a sodium ion (Na⁺) and OH^-.

Scientist 2

An acid is an uncharged or charged substance that donates an H⁺ to another substance (the base) in a chemical reaction, forming a covalent bond. A base is an uncharged or charged substance that accepts an H⁺ from another substance (the acid) in a chemical reaction, forming a covalent bond.

In the reaction of HCl with H₂O, HCl is an acid because it donates an H⁺ to the H₂O. A covalent bond forms between the donated H⁺ and the H₂O, producing a hydronium ion (H₃O⁺) and Cl^-. In this reaction, H₂O is a base because it accepts the H⁺ from HCl.

Scientist 3

An acid is an uncharged or charged substance that accepts a pair of electrons from a base (an uncharged or charged substance that donates the pair of electrons) in a chemical reaction. As the electrons are transferred, a new covalent bond forms between the atom in the acid that is accepting the electrons and the atom in the base that is donating the electrons. At the same time, an existing bond within the acid is broken.

In the reaction of HCl with H₂O, HCl is an acid because it accepts a pair of electrons from H₂O. A covalent bond forms between the H atom of HCl and the O atom of H₂O, and, at the same time, the bond between the H atom and the Cl atom in HCl is broken. This produces H₃O⁺ and Cl^-. In this reaction, H₂O is a base because it donates the pair of electrons to the H atom of the HCl molecule.

39. Based on Scientist 3’s model, which of these can never act as a base in a reaction: an individual atom of H or an individual atom of O ? An atom of:

A. H, because it has less than 2 electrons.

B. H, because it has more than 2 electrons.

C. O, because it has less than 2 electrons.

D. O, because it has more than 2 electrons.

Answer and Explanation

Your Answer is

Correct Answer is A

Explanation

according toScientist 3First paragraph, first sentence, brackets a base…donates the pair of electrons.According to common sense,HAtom can only carry one electron at most, so it cannot give two electrons to other substances, obviouslyHThe atom cannot be like a base.