The amount and concentration of a certain substance solution is prepared in question, and when the v

When we read, we look through the straight line determined by the scale mark and the concave surface of the liquid, so looking down at the reading when setting the volume will cause the amount of water to be added is too small, and the amount and concentration of solute substances will be too large.

Volumetric settingWhen looking down at the tick marks, it will make the preparationSolution concentrationHigh, the specific analysis is as follows:

Volumetric flasks are used.

When the accurate concentration solution is configured, when the water is still 1 to 2 cm away from the engraved line, use the rubber head dropper 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, so that it reaches the process of the engraved line;

Influencing factors: line of sight: looking up - the amount used is greater than the actual amount, looking down - the amount used is less than the actual amount;

It can be seen that looking down at the scale mark when setting the volume will cause the amount of water to be added to be small, so the concentration of the solution will be high.

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.Burette.

Whether it is used for acid or alkali (whether it is washed after use).

3.Observe whether the burette needs to be blown, the burette marked "blow" needs to be blown, and its slag rolling residue does not need to be blown. (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, the amount will be reduced if the amount is quiet).

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 settingWhen looking up at the tick marks to make the preparationSolution concentrationIt is larger than the actual one, and the concentration of the solution prepared by looking down at the scale is smaller than the actual one. Volumetric flasks are used.

When preparing the exact concentration of the solution, when the water is still 1 to 2 cm away from the scale mark, use the rubber head dropper to absorb water and pour 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 process of the scale mark.

Volume determination is carried out in a volumetric flask, usually with a beaker.

Preparation of reagents, such as 1L of reagents, can be prepared in a beaker to about 900ml to 950ml, transferred to a volumetric flask, further add solvent, add to the concave liquid surface 2 to 3 cm away from the volumetric flask scale, let stand for 1 to 2 minutes, and then use the rubber head dropper to drop to the scale line and the lowest part of the liquid calling surface, cover the stopper, flip and shake well.

Definition of volumetric volume

Constant volume is the use of volumetric flasks to configure the accurate concentration of the solution, when the water is still 1 to 2 cm away from the engraved line, use the rubber head dropper to absorb water into the volumetric flask, and the line of sight is level with the lowest part of the concave liquid level, so that it reaches the process of the engraved line, another explanation, the fixed volume is actually a step after the transfer of a small beaker and the drainage of the glass rod, that is, when the transferred solution is 2 to 3 cm away from the concave liquid surface of the volumetric flask, the rubber head dropper is used to drip to the lowest part of the liquid level and the manuscript scale, this process is called volume.

The volume is generally carried out in a volumetric flask, and the reagent is generally prepared with a beaker, such as a 1L reagent, which can be prepared to about 450ml to 500ml in the beaker first, transferred to the volumetric flask, and further added solvent mainly for water, added to the concave liquid surface 2 to 3 cm away from the scale of the volumetric flask, let it stand for 1 to 2 minutes, and then use the rubber head dropper to drop the wax to the scale line tangent to the lowest part of the liquid level, cover the stopper, flip and shake well.

Looking down at the scale mark when setting the volume will make the concentration of the prepared solution high, the specific analysis is as follows:

Constant volume is the process of using a volumetric flask to configure an accurate concentration solution, when the water is still 1 to 2 cm away from the engraved line, 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, so that it reaches the process of the engraved line;

Influencing factors: line of sight: looking up - the amount used is greater than the actual amount, looking down - the amount used is less than the actual amount;

It can be seen that if you look down at the scale mark when setting the volume, the amount of water added will be small, so the concentration of the solution will be high.

Because there is only one scale mark for the volumetric flask used in the volume setting, if you look up at the volume, the actual volume will be larger, so the concentration will be low; If you look down at the fixed volume, it will make it solid.

The international volume is small, so the concentration is high; Icon.

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.

Step 1: Calculation.

Step 2: Weighing: Weigh the solute on a balance and pour it into a small beaker. Step 3: Add an appropriate amount of distilled water to a small beaker with solute in Sheng Wuheng, and mix to dissolve.

Step 4: Pipetting: Inject the solution into the volumetric flask along the glass rod. Step 5: Washing: Wash the beaker 2-3 times with distilled water and pour into a volumetric flask. After 100180°, stand upside down again and stir with a glass rod.

The concentration is on the low side.

When looking up at the scale mark, it must be that the water added exceeds the scale line before it is considered to be just to the scale line, and the volume of the solution is already large and the concentration is low.

This kind of whether the result caused by looking up and down is too large or low must not be memorized, and it is necessary to draw a diagram for analysis, because the scale characteristics of various instruments are different. For example, the higher the graduated cylinder goes, the larger the scale, and the lower the burette graduation. There is also the assumption that if you look up, there is a difference between the error caused by the reading of liquid in a container and the difference caused by adding liquid to it.

If it is low, the amount of HCl does not change, the volume of the solution increases, and the molecule (the amount of the solute) does not change, the denominator (the volume of the solution) increases, and the fraction as a whole (the amount and concentration of the substance) decreases.