Question

question 1
12.5 pts
which of the following statements about the stationary and mobile phases in thin layer chromatography is (are) true?
i. the stationary phase is made of silica - gel.
ii. the stationary phase is a non - polar solvent.
iii. the mobile phase is water.
iv. the mobile phase is a solvent less polar than silica - gel.
options:
i, ii, and iii
ii and iii
iv only
i and iv

Explanation:

1. Analyze Statement I: In thin - layer chromatography (TLC), the stationary phase is commonly silica - gel. So Statement I is true.
2. Analyze Statement II: The stationary phase in TLC (silica - gel) is polar. The stationary phase is not a non - polar solvent. So Statement II is false.
3. Analyze Statement III: The mobile phase in TLC can be a solvent (like a mixture of organic solvents), and water can be part of the mobile phase in some cases (e.g., in normal - phase TLC with aqueous - organic mixtures or in reverse - phase TLC concepts). But more accurately, the mobile phase is a solvent system, and it can have polar components. However, the key here is that the stationary phase is polar (silica - gel), and the mobile phase in normal - phase TLC is less polar than the stationary phase. But the statement "The mobile phase is water" is not always true. In normal - phase TLC, the mobile phase is usually less polar organic solvents. In reverse - phase TLC, the stationary phase is non - polar and the mobile phase is more polar (can include water). But the general statement "The mobile phase is water" is not a universal truth for TLC. Wait, maybe I made a mistake. Let's re - evaluate. The stationary phase (silica - gel) is polar. In normal - phase TLC, the mobile phase is a less polar solvent (like hexane/ethyl acetate). In reverse - phase TLC, the stationary phase is non - polar (e.g., C18 - bonded silica) and the mobile phase is more polar (often aqueous - organic mixtures, so water can be a major component). But the question is about thin - layer chromatography in general. The statement "The mobile phase is water" is not a correct general statement. So Statement III is false? Wait, no, maybe the question has a different context. Wait, let's check Statement IV: The mobile phase is a solvent less polar than silica - gel. In normal - phase TLC (where stationary phase is silica - gel, polar), the mobile phase is less polar than the stationary phase. So Statement IV is true.
4. So Statements I and IV are true.

Answer:

O I and IV