Question 33 Answer and Explanation _ACT December 2019 Form C03 Science Section

Passage V

Liquid H₂O can be broken down into hydrogen gas（H₂）and oxygen gas (O₂) by electrolysis according to the following chemical equation:

2H₂O → 2H₂ + O₂

A scientist performed an experiment to study the electrolysis of H₂O using electricity generated from sunlight.

Experiment

Steps 1-5 were performed daily for 12 months:

1. A tank fitted with 2 electrodes一an anode (where O₂ would be produced) and a cathode (where H₂ would be produced)—was assembled. Each electrode was suspended in an inverted plastic tube, and each tube was marked to allow gas volume to be measured.

2. Four liters (4.0 L) of a 25% by mass aqueous solution of sodium hydroxide (NaOH) was added to the tank. As a result, the tubes were completely filled with the solution.

3. At 8:00 a.m., a rectangular solar cell was attached to the electrodes and placed next to a particular south-facing window for 8 hr. (Figure 1 shows the apparatus at the initiation of electrolysis.)

4. Eight hours later, the solar cell was detached from the electrodes, and the amount of H₂ that had been produced was measured.

5. The tank, tubes, and electrodes were cleaned and dried for reuse.

Figure 2 shows the total volume of H₂ produced (in L) in each month of the experiment. Table 1 shows the average solar irradiance (power per unit area), in watts per square meter (W/m²), at the location of the solar cell during each month of the experiment.

Figures and table adapted from Sergii Bespalko, "Hydrogen Production by Water Electrochemical Photolysis Using PV-Module. " @2011 by Sergii Bespalko.

33. Suppose the experiment was repeated, except that the scientist added only pure liquid H₂O to the tank in Step 2. Based on the description of the experiment, would this change have more likely resulted in more H₂ being produced or less H₂ being produced?

A. More H₂; pure liquid H₂O has more ions and thus higher electrical conductivity than does an aqueous NaOH solution.

B. More H₂; pure liquid H₂O has fewer ions and thus lower electrical conductivity than does an aqueous NaOH solution.

C. Less H₂; pure liquid H₂O has more ions and thus higher electrical conductivity than does an aqueous NaOH solution.

D. Less H₂; pure liquid H₂O has fewer ions and thus lower electrical conductivity than does an aqueous NaOH solution.

Answer and Explanation

Your Answer is

Correct Answer is D

Explanation

Pure water does not conduct electricity at all, it is the ionic compounds in the water that conduct electricity, that is to say, without NaOH, electrolysis will not occur at all