What are the advantages and disadvantages of fixed weighing method and decreasing weighing method? Under what circumstances did you choose these two methods?

Advantages and disadvantages of the fixed mass weighing method: The advantages are that it is used to weigh a certain mass of reagents, and the weighed objects are required to be stable in the air, not absorbing moisture, not absorbing moisture, simple to operate and easy to control the amount. The disadvantage is that for absorbent products, the result error is large.

This method is used to weigh reagents (such as reference materials) or samples with fixed mass. This kind of weighing operation is very slow, and it is suitable for weighing powder or small particles that are not easy to absorb moisture and can exist stably in the air (the smallest particle should be less than 0. 1 mg, so as to adjust its quality).

Advantages and disadvantages of the decreasing weighing method: the advantage is that it is used to weigh substances that are easy to absorb water, oxidize or react with carbon dioxide, and the sample weight does not require a fixed value, but only needs to be within the required weighing range; The disadvantage is that it is difficult to control the dosage without changing the operation, which leads to drug waste, but it does not affect the results when weighing hygroscopic samples.

Decreasing method is a weighing method that can continuously weigh multiple samples and save time. Suitable for continuous weighing of multiple samples by decrement method. Because its quantity is allowed to fluctuate within a certain range, it is also used to weigh samples that are easy to absorb moisture, oxidize or react with carbon dioxide.

Extended data:

Constant mass weighing method: weigh the empty container with the sample by direct weighing method, add the weight of the sample to the existing weight, and then slowly add the sample into the container with a spoon until the balance reaches balance.

Decreasing weighing method weighing steps:

1, first weigh the accurate quality of the sample and weighing bottle m 1.

2. Pour a part of the sample in weighing bottle into the container to be filled, and pour almost the required amount. (Tilt weighing bottle, tap the bottle mouth with the bottle cap, and the sample will slowly fall into the container. When it is close to the required weight, tap the bottle mouth with the bottle cap to make the sample stuck on the bottle mouth fall, and at the same time, weighing bottle will slowly stand upright).

3. Cover the weighing bottle, put it on the balance, and accurately weigh its mass m2.

4. The difference between the two masses is the quality of the sample, and multiple samples can be weighed continuously by the same method.

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