A balance is a commonly used instrument when we do experiments, especially in quantitative analysis, it is even more essential. The accuracy of the balance weighing will also directly affect our final analysis results. Therefore, it is very important to choose and use the balance correctly.
Before introducing different balances, let me tell you about two important indicators of the balance: the maximum load capacity and the sense of capacity. The maximum load capacity is also the maximum weight, which means the maximum value that the balance can weigh. The amount of sense is also called the division value or the minimum accurate weight, which is the quality corresponding to one division of the balance scale.
Classification of balances
According to the construction principle and sense of the balance, the balance has different classifications.
1. Classification according to the structure principle of the balance
(1) Mechanical balance
Mechanical balance is also called lever balance, its weighing principle is the use of lever principle. There are equal-arm double-disc balances and unequal-arm double-knife single-disc balances.
(2) Electronic balance
The weighing principle of electronic balance is to balance by electromagnetic force. It is simple in structure and easy to use, and is also a commonly used balance in our laboratory.
2. Classify according to the sense of balance
(1) Ordinary balance
Ordinary balance is a balance with a sense of between 0.1 and 0.001g, suitable for general rough weighing, weighing a few grams to several hundred grams of substances.
(2) Analytical balance
The sensitivity of the analytical balance is 0.0001g, which is usually called the balance of ten thousandths of a gram, and is suitable for weighing samples, standard samples, etc.
A microbalance is a balance with a sensitivity of 0.01mg, called a 1/100,000 gram balance, which is suitable for semi-micro and micro-analysis in chemical analysis. Having said that, I think it is necessary to explain what is microanalysis and semi-microanalysis. Chemical analysis includes macroanalysis, semi-microanalysis, microanalysis and ultramicroanalysis. Among them, the allowable amount of the tested substance for micro-analysis is only about 1% of the constant, the weight is about 1~15 mg, and the volume is about 0.01~2ml. The amount of the measured substance in semi-micro analysis is only 1/25-1/10 of the constant, and the mass is about 10 mg-100 mg. It is an analysis method between the macro-analysis and the micro-analysis. The amount of the sample used in the constant analysis is generally more than 0.1g, and the volume of the sample used is more than 10ml.
Rules of use of the balance
1. The balance room should be kept clean and dust-proof, the temperature should be stable, the fluctuation range should be less than 0.5°C, the room temperature should be kept at 15~30°C, the humidity should be kept at 55%~75%, avoid direct sunlight, and put silica gel desiccant in the balance.
2. The same balance and weight should be used for the same experiment.
3. Check whether the balance is in good condition and clean before and after weighing.
4. When weighing, the maximum load of the balance cannot be exceeded. The weighing object must be placed in a clean vessel, especially for volatile, corrosive and hygroscopic substances, which should be covered and sealed. Substances that are too cold or too hot cannot be weighed.
5. The weighing object should be placed in the center of the weighing pan, and the balance door should be closed. The reading can only be read after the reading is stable. After the weighing object is placed, the balance should be closed.