The problem of volumetric flask capacity determination, the correct operation of volumetric flask vo

Because there were water droplets hanging on the wall of your bottle, the water droplets did not go down when the volume was fixed, and then the natural liquid level was higher after a long time.

Another point is that the temperature of the volumetric flask may not drop to room temperature, which causes the bottle to shrink later, causing the liquid level to rise.

The correct operation should be to use a small amount of water first, which can be heated until the solute is fully dissolved, and then transferred to a clean volumetric flask.

The temperature must be kept at room temperature, otherwise it will also cause inaccurate volume.

If there are so many more, it means that multiple factors are acting at the same time.

I found that you are very brain-dead, go back and do another experiment yourself, if it is cold to absolute room temperature for a long time, use a dry volumetric flask, use the one that has been dissolved, and sit down without this problem.

What's the point of discussing this more.

What are you dissolving? Will it decompose when heated? Will it produce dissolved gases?

After heating, the volumetric flask is not accurate! Volumetric flasks cannot be heated.

No, because solutes are exothermic or endothermic when dissolved.

You put it in a volume bottle to dissolve.

The temperature affects the accuracy of the volume control bottle (precision instrument).

Precision! To dissolve the solute in a beaker. Stand to cool down in can be transferred.

It could be that you have deformed the bottle when you heat it.

I don't know, but the volumetric flask can't be heated.

When the volumetric flask is determined, a rubber head dropper should be used to titrate to the concave liquid level of the liquid in the volumetric flask and the scale line is level, and then shake it upside down, after mixing the liquid, sometimes the liquid level will be lower than the scale line, which is a normal situation, and the solvent must not be added at this time. A volumetric flask is a precision instrument used to accurately prepare a solution of a certain concentration, also known as a measuring flask. <

When the volumetric flask is determined, a rubber head dropper should be used to titrate to the concave liquid level of the liquid in the volumetric flask and the scale line is level, and then shake it upside down, after mixing the liquid, sometimes the liquid level will be lower than the scale line, which is a normal situation, and the solvent must not be added at this time. A volumetric flask is a precision instrument used to accurately prepare a solution of a certain concentration, also known as a measuring flask.

The volume is carried out in a volumetric flask, and the reagent is generally prepared with a beaker, such as a 1L reagent, which can be prepared in a beaker to about 900ml to 950ml, transferred to a volumetric flask, further added solvent, added to the concave liquid surface 2-3 cm away from the scale of the volumetric flask, and then allowed to stand for 1-2 minutes, and then use the rubber head dropper to drop to the scale line and the lowest part of the liquid level, cover the stopper, flip and shake well.

Influencing factors. 1.There is an easy-to-remember mantra for looking up – the amount used is greater than the actual amount, and looking down - the amount used is less than the actual amount): look down to see high, look up to see low.

2.Whether the burette is used for acids or bases (whether they are cleaned after use or not).

3.Observe if the burette needs to be blown, the burette marked "blow" needs to be blown, and the rest do not. (If you blow a pipe that doesn't need to be blown, you actually add more liquid than the theory requires, and if you don't blow the pipe that needs to be blown, you actually add less liquid than the theory requires).

4.Whether there are air bubbles at the lower end of the burette (if so, there is less of a small amount).

5.Moisturizing or not (without rinsing, the liquid concentration table is small, and the dosage is more than the actual dosage).

6.If the volume is fixed after flipping and shaking, it will cause too much water to be added, resulting in a small concentration of the solution.

7.Burettes and volumetric flasks are marked with the operating temperature.

Volumetric flasks are volume-in containers. After the volume is fixed, the exact concentration of the substance in the solution can be calculated according to the amount of substance in the volumetric flask (mol).

Constant volume: quantify the solution that needs to be moved in (the error is not greater than that of moving into a volumetric flask, and dilute to the scale and shake well. There are two ways to move this in:

1. Accurately weigh the solid soluble substances in the small beaker, after they are completely dissolved, drain them with a stirring rod (glass rod) and move them into the volumetric flask; 2. Dilute the solution: Pipette the concentrated solution into the exact volume and volumetric flask.

Pipetting: When applying solutions in volumetric flasks, most are pipetted with a pipette. The method is to wash the pipette clean, then rinse it with the solution in the volumetric flask 3 times and then pipette it directly.

For the specific operation details, the teacher will demonstrate in the laboratory class, and cannot be clearly explained in words.

Drain with a glass rod, the glass rod is slightly tilted, do not touch the volumetric flask, wash the remaining water in the beaker 2 3 times and then pour it into the volumetric flask, change to a rubber head dropper from the scale 2 3cm, look up, stop when the concave liquid level reaches the scale line, cover the lid and shake well, do not add water!

Note: Before using the volumetric flask, wash it with water, close the cap, turn it upside down, turn the cap 180°, if it does not leak, confirm that the volumetric flask does not leak water and air.

Method of pipetting: Wash the pipette clean, then rinse it three times with the solution in the volumetric flask and pipette directly.

There are two ways to determine the volume. One is solid, and the solubles that are accurately weighed are put into a small beaker, drained with a glass rod, and quantitatively introduced into a volumetric flask. The second is liquid volumetric, in which the concentrated solution is removed from the exact volume in a volumetric flask.

Because the total amount of the substance has not changed, it is the original so many moles, the size of the volumetric flask is certain, and the amount of water in it is equivalent to you adding some water to it first, and the amount of water is the size of the volumetric flask, and the amount of the substance is certain, so of course the amount and concentration of the substance will not change.

Make the solute x grams.

The volume scale is 1000ml

When the scale is not exceeded, its volume is 999ml

When the scale is exceeded, the volume is 1001ml

x/1001) < x 1000) < x 999) so the concentration will be smaller beyond the scale.

20 3) * (50 5) = 200 3 times.

The solution was diluted a total of 200 3 times during this cavity.

Move 3ml to a 20ml volumetric flask to set the volume, which means add 3ml of water to the volume of 20ml, and dilute it by 20 3

Move another 5ml to a 50ml volumetric flask, (this should also be fixed, right?) You didn't say it in the question) If the volume is also fixed, it is to add water to the volume of 50ml, and dilute it by 50 5, so the solution in this process is 200 3 times.

This is wrong, and continuing to add water to the volumetric flask to the scale mark will result in the solution being dispensed with a lower concentration than required.

No, because solutes are exothermic or endothermic when dissolved.

You put it in a volume bottle to dissolve.

The temperature affects the accuracy of the volume control bottle (precision instrument).

Precision! To dissolve the solute in a beaker. Stand to cool down in can be transferred.

It could be that you have deformed the bottle when you heat it.

Encyclopedia is a good thing, why don't you know how to use it.

The following **encyclopedia.

Constant volume is the process of using a volumetric flask to configure an accurate concentration of solution, when the water is still 1 to 2 cm away from the scale mark, the rubber head dropper is used to absorb water and inject it into the volumetric flask, and the line of sight is level with the lowest part of the concave liquid surface to make it reach the scale mark.

I gave you 10,000 yuan and you lost a few of them yourself, can you say that I didn't give you the full amount?!

Volumetric flasks are mainly used to accurately prepare solutions of a certain molar concentration. It is a slender-necked, pear-shaped, flat-bottomed glass bottle with a grinding stopper. The neck of the bottle is engraved with a reticle, and when the liquid in the bottle reaches the reticle at the specified temperature, its volume is the volume indicated on the bottle.

A volumetric flask of one size can only be measured. Commonly used volumetric flasks are available in milliliters and other sizes. The method of preparing the solution using a volumetric flask is:

1) Check the stopper for water leakage before use. The specific operation method is: fill half a bottle of water in the volumetric flask, plug the cork tightly, hold the stopper with the index finger of the right hand, and hold the bottom of the volumetric flask with the five fingers of the other hand, and turn it upside down (the mouth of the bottle is facing down) to observe whether the volumetric flask is leaking.

If there is no water leakage, the bottle is upright and the bottle stopper is rotated 180°, then stand upside down again to check whether there is water leakage, if there is no water leakage around the volumetric flask stopper during two operations, it means that the volumetric flask is not leaking. Only volumetric flasks that have been inspected for non-leakage can be used.

2) Put the accurately weighed solid solute in a beaker and dissolve it with a small amount of solvent. The solution is then transferred to a volumetric flask. In order to ensure that all solutes can be transferred to the volumetric flask, the beaker should be washed several times with solvent and all the washing solution should be transferred to the volumetric flask.

Drainage with a glass rod is used during transfer. The method is to place one end of the glass rod against the inner wall of the volumetric bottleneck, and be careful not to let other parts of the glass rod touch the mouth of the volumetric flask, so as to prevent the liquid from flowing to the outer wall of the volumetric flask.

3) When the liquid level of the liquid added to the volumetric flask is about 1 cm away from the reticle, it should be carefully added with a dropper, and finally the meniscus surface of the liquid is exactly tangent to the reticle. If the water is added beyond the scale mark, it needs to be reconstituted.

4) Tightly close the cork, and use the method of inverting and shaking to mix the liquid in the bottle evenly. If the liquid level is found to be lower than the scale mark after standing, this is because a very small amount of solution in the volumetric flask is lost by wetting at the bottleneck, so it does not affect the concentration of the prepared solution, so do not add water to the bottle, otherwise, the concentration of the prepared solution will be reduced.

The following points should be taken into account when using volumetric flasks:

1) The volume of the volumetric flask is specific, and the scale is not continuous, so one type of volumetric flask can only prepare the same volume of solution. Before preparing the solution, it is necessary to figure out the volume of the solution to be prepared, and then choose a volumetric flask of the same size.

2) The substances that are easy to dissolve and do not generate heat can be directly dissolved in the volumetric flask with a funnel, and other substances can not be dissolved in the volumetric flask, and the solute should be dissolved in the beaker and transferred to the volumetric flask.

3) The total amount of solvent used to wash the beaker should not exceed the reticle of the volumetric flask.

4) The volumetric flask cannot be heated. If the solute is exothermic during the dissolution process, it is necessary to wait for the solution to cool down before transferring, because the general volumetric flask is calibrated at a temperature of 20, if the solution with a higher or lower temperature is injected into the volumetric flask, the volumetric flask will expand and contract, and the measured volume will be inaccurate, resulting in the inaccurate concentration of the prepared solution.

5) The volumetric flask can only be used to prepare the solution, not to store the solution, because the solution may corrode the bottle body, so that the accuracy of the volumetric flask is affected.

The solute in the solution is evenly distributed in the solvent, and the oscillating solution will inevitably cause a small amount of solution to adhere to the inner wall near the mouth of the volumetric flask, when you continue to add water, the solute is certain, the solvent increases, and the solution concentration will decrease.