Multiple-choice question: In the indirect iodometry method, why is the iodometric flask placed in a dark place? ( )

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It is placed in the dark to prevent iodine from evaporating. At the same time, excessive shaking should be avoided during titration to prevent iodide ions from being oxidized by air.

It is 1, to prevent decomposition and volatilization.

2 Avoid oxidation, as iodide ions are prone to oxidation under the catalysis of sunlight

1. Avoid the volatilization of iodine. Only this answer is the most reliable

Multiple choice is okay, right? I think 1.2 is fine too

Keeping it at a low temperature is also to prevent volatilization (sublimation); it’s not possible to choose both. Choose 1. This post was last edited by Beifang Yunque on 2009-2-26 09:10.]

The sources of error in the iodometric method are, on the one hand, the volatilization of I2, and on the other hand, the oxidation of I-. Measures to prevent the evaporation of I2: (1) Room temperature. (2) Adding an excess of I- converts I2 to I3-, increasing its solubility. 　　Measures to prevent I- from oxidizing: (3) Protect from light. (4) After I2 is generated, titrate it immediately with Na2S2O3 ； The titration rate was appropriately increased. Personally, I think oxidation should be avoided

My answer is 2, but 1 is also a factor; it seems the key word in this question is hidden somewhere.

1; However, I personally think that both 1 and 2 make sense

I choose 1 to avoid the volatilization of I2. The repeated indirect iodometry method: The indirect iodometry method, also known as the titration iodine method, utilizes the reducing property of I- (usually KI) to react with oxidizing substances and generate free iodine; this free iodine is then titrated using a standard solution of a reducing agent (Na2S2O3) in order to determine the amount of oxidizing substance present. For example, in the copper salt in question, the copper content causes I2 to be precipitated upon reaction with an excess of KI under acidic conditions. Then it is titrated with a Na2S2O3 standard solution. This reaction process is considered the basis of the iodometric method. To determine the endpoint of the iodimetry method, starch is commonly used as an indicator; for the indirect iodimetry method, the endpoint is reached when the blue color changes to colorless. Starch should be added near the end of the titration; if added too early, it will absorb more I2, causing errors in the titration results.

Standard answer: 2. This is a typical question in analytical chemistry exams. Key points: Iodometric method: use an iodometer flask, allow it to stand still, keep it away from light, and let it rest for several minutes. Reason: Iodide ions are oxidized by air, and this oxidation process accelerates with exposure to light and increased acidity; therefore, option 2 is chosen. The measure to prevent the evaporation of iodine is to use an iodometer flask and avoid shaking it vigorously.

I have a gentle question: can light cause iodine to evaporate?

Among the options, 1 is the closest. But personally, I think a better way to put it is to prevent iodine from decomposing when exposed to light.

Iodine is volatile and readily undergoes the following reaction under light: I2 + H2O → HI + HIO. I2 solutions should be stored in brown bottles with tight lids, in a dark place. The iodine flask used in the indirect iodometry method, which has a stopper, also needs to be sealed with water in order to prevent the evaporation of the iodine produced. It is placed in a dark place to prevent disproportionation reactions under sunlight. Therefore, the answer should be 1. Of course, I- is easily oxidized by oxygen from the air in acidic solutions, resulting in the release of I2: 4I- + 4H+ + O2 → 2I2 + 2H2O. Therefore, to reduce contact between I- and air, avoid excessive shaking during titration. This post was last edited by xwtsq on 2009-2-26 20:03]

Haha, why are there so many options to choose from? ? ? It is necessary to strengthen basic studies :o