This chemistry question involves key chemical concepts and calculations. The detailed solution below walks through each step, from identifying the reaction type to computing the final answer.
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Step 1: Identify the properties of caustic potash (potassium hydroxide, KOH). Caustic potash (KOH) is a strong base. It has two main reactions/properties relevant to air: • It reacts with acidic gases like carbon dioxide (CO_2). The reaction is: 2KOH(aq) + CO_2(g) K_2CO_3(aq) + H_2O(l) • It is hygroscopic, meaning it readily absorbs water vapor (H_2O) from the air, acting as a drying agent. Step 2: Analyze the composition of air and what remains after passing through caustic potash. Air is primarily composed of nitrogen (N_2), oxygen (O_2), argon (Ar), carbon dioxide (CO_2), and water vapor (H_2O). After passing through caustic potash, the CO_2 and H_2O will be removed. N_2, O_2, and noble gases (like Ar) are unreactive with KOH and will remain. Step 3: Evaluate each option. A. contain more oxygen than nitrogen: Air is approximately 78% nitrogen and 21% oxygen. Since neither reacts with KOH, their relative proportions will not change in a way that makes oxygen more abundant than nitrogen. This statement is incorrect. B. rekindle a glowing splint: A glowing splint test is for oxygen. While oxygen remains, the concentration of oxygen in the remaining gas (mostly N_2 and O_2) is not high enough to rekindle a glowing splint, as air itself does not do this. This statement is incorrect. C. have no action on lime water: Lime water (Ca(OH)_2 solution) is used to test for carbon dioxide. If CO_2 is present, it reacts with lime water to form insoluble calcium carbonate, making the solution milky: Ca(OH)_2(aq) + CO_2(g) CaCO_3(s) + H_2O(l). Since caustic potash removes CO_2, the air sample will no longer contain CO_2 and thus will have no action on lime water. This statement is correct. D. contain no water vapour: Caustic potash is a strong desiccant and will absorb water vapor from the air. Therefore, the air sample will be dried and contain very little to no water vapor. This statement is also correct under ideal conditions. E. be free of noble gases: Noble gases are unreactive and will not be absorbed or reacted with by caustic potash. They will remain in the air sample. This statement is incorrect. Step 4: Choose the best answer between C and D. Both C and D describe correct consequences of passing air through caustic potash. However, in chemistry questions, the removal of CO_2 by a strong base is a characteristic chemical reaction, and the "no action on lime water" is a direct and specific chemical test result for the absence of CO_2. While KOH also dries air, its role as a CO_2 scrubber is often highlighted as a primary chemical function. Therefore, option C is generally considered the most appropriate answer in this context. The final answer is C. That's 2 down. 3 left today — send the next one.