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About the volumetric flask preparation solution process

Time:2018/10/29   Pageviews:13    Share:
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1. Instruments used to prepare solutions in volumetric flasks:

1. Beaker, volumetric flask, glass rod, plastic dropper, analytical balance, medicine spoon (for solid solute use),10mm HPLC vilas pipette (for liquid solute use)

2. Volumetric flask

1). Construction: grinding, neck, pear-shaped flat bottom

2). Features: 1 indicates the temperature and volume on the volumetric flask. 2 The capacity bottleneck has a tick mark.

3). Scope of use: It is specially used to prepare a solution of a certain volume and a certain concentration of a certain substance.

4). Note: 1 Check leak before use. 2 Do not install hot or cold liquid. 3 Cannot be used to dissolve solid materials or to store liquids or to carry out chemical reactions.

3. Use the volume bottle six bogey: one should not use the volumetric flask for dissolution (volume is not accurate), the second bogey directly into the volumetric bottle (will spill to the outside); three bogey add water beyond the tick mark (low concentration); The reading is looking up or down (the concentration is low, and the concentration is high); the five bogey do not wash the glass rod and the beaker (low concentration); the six bogey standard solution is stored in the volumetric flask (the volumetric flask is a measuring device, not a container).

2. Steps for preparing the solution with a volumetric flask:

The whole process has eight steps of calculation, weighing, dissolving, cooling, transferring, washing, constant volume, shaking and bottling. The formula: meter, quantity, solution, cold, transfer, wash, set, shake

The preparation process of the solution is illustrated by taking 500ml of 0.1mol/L NaCO3 solution as an example.

1. Calculation: the amount of NaCO3 substance = 0.1 mol / L × 0.5 L = 0.05 mol, from NaCO3 molar mass 106 g / mol, then NaCO3 mass = 0.05 mol × 106 g / mol = 5.3 g

2. Weighing: Weigh 5.300g with analytical balance, pay attention to the analysis of the use of the balance.

3. Dissolution: completely dissolve in a beaker with 100 ml of distilled water and stir with a glass rod (note: should be cooled, 10mm HPLC vilas  not dissolved in the volumetric flask)

4. Transfer, washing: Transfer the dissolved solution into a 500ml volumetric flask for thinning the volume of the volumetric bottle. To avoid spilling the solution, do not let the solution flow down the bottle wall above the scale line and drain with a glass rod. In order to ensure that the solute is transferred to the volumetric flask as much as possible, the beaker and the glass rod should be washed two or three times with distilled water, and the solution after each washing is injected into the volumetric flask. Gently shake the volumetric flask to allow the solution to mix well. (draining with a glass rod)

5. Constant volume: When adding water to the scale of 2-3 cm, use a plastic pipette and add distilled water to the scale. This operation is called constant volume. When setting the volume, pay attention to the zoi low point of the solution concave surface and the tick mark. The eye line of sight and the tick mark are horizontal, so you can't look down or look up, otherwise it will cause errors.

6. Shake well: The concentration of the solution after constant volume is not uniform. To close the volume bottle stopper, use the index finger to hold the stopper, hold the bottom of the bottle with the finger of the other hand, and invert and shake the volume bottle several times. , so that the solution is mixed evenly. This operation is called shaking.

7. Shake the Na2CO3 solution after constant volume. Pour the prepared solution into the reagent bottle, cap the stopper, and label it. Which operations may cause errors in solution concentration during the preparation of the solution?

Three. Capacity bottle process analysis:

According to the reason, the cause of the error is whether the "solute nB" and the "solution volume V" are accurate, so the possibility of error may be:

1. Whether the weighing of solid drugs and the amount of liquid drugs are accurate.

2. A reagent that dissolves in water to exotherm or absorb heat. If it is not cooled after dissolution, it will cause a volume deviation of the solution, causing an error in the concentration of the solution.

3. When the solution is transferred into the volumetric flask, a small amount of spillage occurs, and the concentration of the solution is low.

4. During the preparation process, the used beakers and glass rods were not washed with distilled water, and the concentration of the prepared solution was low.

5. When the volume is fixed, the reading scale is looked up, the concentration of the obtained solution is low, and the top view is high. Therefore, in the process of preparation, it is necessary to prevent the loss of solute (such as: weighing, draining during pipetting, washing after dissolving), and preventing the volume of the solution from being too large (eg, cooling after dissolution, eye looking up, top view).

Fourth, the main matters needing attention:
1. The volumetric flask is a precision-scale glass instrument that cannot be used to dissolve

2. After dissolving the solute, the solution should be placed and cooled to room temperature and then transferred.

3. Dissolve the beaker and the glass rod for stirring and draining, both need to be washed two or three times after the transfer.

4. Transfer the solution from the small beaker to the volumetric flask. Because the bottle mouth of the volumetric flask is thin, in order to avoid spilling the solution, do not let the solution flow down the bottle wall above the scale line, and drain with a glass rod.

5. When making the volume, pay attention to the lower part of the solution surface and the tangent line. The line of sight and the scale line are horizontal. Do not look down or look up. Otherwise, the error will be caused. The solution will be made smaller in size and the solution concentration will be biased. Big. Looking up is to make the solution volume too large, so that the solution concentration is too small.

6. Once the volume is too much, the preparation process fails. The solution cannot be sucked from the volumetric flask to the scale with a straw.

7. After shaking, it is found that the liquid level is lower than the engraved line, and no additional distilled water can be added. Because the distillate is added to the distilled water to make the liquid surface just tangent to the engraved line, the volume of the solution is just the volumetric flask. Calibration capacity. After shaking, the liquid level will be lower than the score line when the volumetric flask is vertical, because a very small amount of liquid is stuck on the stopper or the 10mm HPLC vilas  grinding. Therefore, it is not necessary to add distilled water after shaking, otherwise the concentration of the solution is low.

This is the end of the introduction of About the volumetric flask preparation solution process. I hope it can help you.


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