How laboratory electronic balance measures solid density
When measuring and analyzing substances in daily laboratories, electronic balances and density test components are often used to measure solid density. Ohaus electronic balances can be used to measure solids with a density greater than the auxiliary liquid density, solids with a density less than the auxiliary liquid density, liquid density, and density of porous materials (such as oil seepage and bearing materials).
First, let's briefly understand the principle of using an electronic balance to measure the density of solids:
1. The density of an object is its mass to volume ratio.
2. The density measurement is based on the Archimedes principle. The principle states that the weight lost by each solid immersed in the liquid is equal to the weight of the liquid it has discharged.
3. Solid density measurement usually uses a known density liquid (for example: water or ethanol) as an auxiliary liquid, which can be calculated by weighing the solid mass to be measured in air (A) and auxiliary liquid (B) successively Find its density.
Before the density measurement, we need to make the following preparations:
1. Electronic balance. The precision of the electronic balance should be selected according to the specific requirements for the accuracy of the measured density data, and the capacity of the electronic balance should be selected according to the volume and weight of the sample being measured. Before the test, the prepared electronic balance needs to be warmed up for a long enough time, and the necessary corrections are made to ensure the accuracy of the measurement data.
2. Test the component. It is necessary to select a suitable test component. For some materials with a large volume that cannot be placed in the weighing chamber, a down-hung test component must be selected.
3. The sample to be tested. Considering the influence of the surface tension of water, in order to measure the accuracy of density, it is recommended that the measured sample weight must be greater than 1g. In order to improve the measurement accuracy, it is recommended to choose samples with regular shapes and small surface roughness.
4. Select the appropriate auxiliary liquid. The general options are: water, alcohol, other. The selection of test auxiliary liquid should be based on the nature of the specific test sample. If it is easy to react with water, alcohol can be used as the auxiliary auxiliary liquid.
After preparing the required equipment and samples, please take the following steps to measure:
1. Open the left or right door of the electronic balance to remove the weighing pan, and insert the density bracket into the electronic balance.
2. Place the bracket in a suitable position above the bracket to ensure that the bracket does not contact the bracket.
3. Place the beaker in the center of the bracket. Insert a thermometer in the beaker to measure the current temperature of the liquid.
4. Inject a reference liquid of known density (usually water or alcohol) into the beaker to ensure that the solid to be tested can be completely immersed in the liquid by more than 1 cm.
5. Place the hanging basket on the fixed bracket to ensure that there are no bubbles on the surface and do not touch the beaker or thermometer (see Figure 2 below)
6. Turn on the electronic balance switch
7. Close the windproof door and tare it;
8. Open the windproof door of the electronic balance and place the measured solid on the weighing arm of the fixed bracket or the weighing pan on the top of the hanging basket; if the mass of the measured solid in the air is greater than 20g, please place it on the top of the hanging basket Weighing in the weighing pan;
Note: For solids with a density less than the density of the auxiliary liquid, the weighing net at the bottom of the hanging basket needs to be reversed to press the object to be measured. If the buoyancy of the solid is greater than the weight of the basket, you must assist in weighing by placing an additional weight on top of the basket. After loading additional weights, tare the electronic balance and start weighing again. As shown in Figure 3 above.
9. Turn off the electronic balance windshields. After the electronic balance is stable, the electronic balance will automatically record the weighing result A (see Figure 4 below);
10. Open the windproof door of the electronic balance, remove the measured solid, close the windproof door and tare it;
11. Open the windproof door of the electronic balance and place the measured solid in the weighing net under the hanging basket, and ensure that no bubbles adhere to the solid surface (you can use a small brush to remove surface bubbles)
12. Close the windproof door of the electronic balance. After the electronic balance is stable, the electronic balance will automatically record the weighing result B. And calculate the density of the solid to be measured according to the density formula.
Note: For Ohaus DV and AR series electronic balances have been set in the electronic balance software, the density data can be read directly without manual calculation, which is healthier.
Electronic balances with density direct reading function are: DV, EP industrial electronic balance, AR, SE; electronic balances with density determination function are: EP, CAV, CP, SPS (can be calculated manually).
Improve the accuracy of solid density measurement results
1. Temperature
Solids are generally not particularly sensitive to temperature changes, but when working with auxiliary liquids during density measurement, the greater influence of temperature on the liquid must be considered.
Generally, the density will be changed in the order of 0.1 ℃ to 1 ℃. This will affect the change of the third decimal place in the measurement result. It is recommended to always consider the temperature of the auxiliary liquid during the solid density measurement.
2. Surface tension of auxiliary liquid
Liquid adhered to the hanging basket will increase the surface quality by 3mg. When the hanging basket is immersed in the auxiliary liquid during the two weighings of the solid (in air and auxiliary liquid), the effect of the increase in the amount caused by the surface tension of the auxiliary liquid is negligible. Because the electronic balance will be peeled before each measurement. To reduce the influence of air bubbles and ensure the maximum possible accuracy, a few drops of wetting agent (not supplied) can be used and added to the auxiliary liquid.
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