The procedure for preparing a solution for a certain amount of a substance

I've just graduated from high school, science student, and I'm going to talk about it

The basic steps are divided into books! Calculate Weigh Dissolve Transfer **Shake well Store in constant volume.

Every step counts!

1. Calculation. It is necessary to calculate how much substance to add, because the capacity of the volumetric flask is standard, so there is no such thing as 249ml and 251ml.

2. Weighing. If it is an acidic or alkaline substance, put it in a beaker to weigh, isn't it the left thing right code First weigh an empty beaker, weigh the item in the beaker, and finally subtract the mass of the beaker. Also, if it's easy to absorb water like sodium hydroxide, be sure to weigh it quickly!

Remember to hand over the balance before weighing

3. Dissolve. Stir slowly in a beaker with a glass rod, taking care not to spill the liquid.

4. Transfer. Transfer to a volumetric flask, use a glass rod to divert the flow, and finally be sure to remember to rinse the beaker and glass rod with clean water, but! This water must end up in a volumetric flask! And! Do not exceed the scale mark of the volumetric flask.

5. Observe whether the concave surface of the horizontal line is the same as the scale mark, if it is less, add some water, and finally be sure to add it with a rubber head dropper, accurately. If it's too much, it's time to dump and reconfigure! So be careful.

Remember, volume setting is after cooling to room temperature! When the temperature of the liquid is not the same as the room temperature, it is not accurate! The temperature is carved on the volumetric flask, too.

6. Storage. Just put it in a safe place

Calculate, weigh or measure, dissolve.

1. Calculation: the mass of the solid or the volume of the liquid measured. 2. Weighing: Pay attention to the accuracy of the balance when weighing solids. 3. Dissolve: generally in a beaker.

. 4. Pipetting: When transferring the liquid of Qiaojube, use a glass rod to drain it. 5. Washing: with distilled water.

Wash the beaker and glass stick 2 3 times with a large wide hand. 6. Fix the volume.

When to the volumetric flask.

When adding water to the scale 1 cm 2 cm, then use the rubber tip dropper to the scale. 7. Shake well: At this time, if the liquid level is lower than the scale line, do not add water.

8. Bottling: The volumetric flask cannot hold the liquid for a long time, and should be contained in the designated reagent bottle and labeled.

Calculation formula:

Prepared with liquid reagents:

According to the principle of equality of solute mass before and after dilution, the formula is obtained:

1ρ1 v1=ω2ρ2 v2

1: Diluted mass fraction.

1: Density v1: The volume of the solution to be dispensed.

2: Concentrated solution mass fraction 2: Density v2: The volume of concentrated solution is required.

Example: To prepare 1000ml of 20% sulfuric acid solution, 96% concentrated sulfuric acid is required.

How many milliliters? Look up the table and know: 1=when 20%; 2=at 96%.

Substitution formula: 20%.

v2=The following points should be taken into account when using volumetric flasks:

1. The solute cannot be dissolved in the volumetric flask, and the solute should be dissolved in the beaker and transferred to the volumetric flask.

2. The total amount of solvent used to wash the beaker should not exceed the marking line of the volumetric flask, and once exceeded, it must be re-formulated.

3. The volumetric flask cannot be heated. If the solute is exothermic during dissolution, it is necessary to wait for the solution to cool before transferring, because the temperature will increase and the bottle will expand and the measured volume will be inaccurate.

4. The volumetric flask can only be used to prepare the solution, and cannot store the solution for a long time or for a long time, because the solution may corrode the bottle body, so that the accuracy of the volumetric flask will be affected.

5. The volumetric flask should be washed in time after use, the cork should be plugged, and a paper strip should be clamped between the stopper and the bottle mouth to prevent the cork from sticking to the bottle mouth.

6. The volumetric flask can only prepare a certain capacity of solution, but generally retains 4 significant digits (such as: can not be estimated to change the number after the decimal point because the solution exceeds or does not reach the scale mark, can only be reconfigured, so the volume of the solution must be written when it is.

Here's how to prepare the solution:

1. Direct method.

A certain amount of dried reference material is accurately weighed on an analytical balance, dissolved and quantitatively transferred to a calibrated volumetric flask.

medium, with distilled water.

Dilute to scale and shake well.

2. Calibration method.

Calibration: A reference substance or a solution of known exact concentration is used to determine the concentration of a standard solution.

The process of operation. Direct calibration (use the reference material to carry out the covering, transport and concealment calibration hall): accurately weigh a certain amount of reference material, dissolve it in water and titrate it with the standard solution to be measured, until the medical education network collects and sorts out the quiet shed reaction completely.

Indirect calibration: The standard solution to be tested is calibrated with another standard solution of known concentration.

Note: The standard solution is prepared and calibrated by a special person.

Standard solutions should be calibrated at regular intervals.

Each vial of reagent solution must be labeled with the name, specification, concentration, and configuration.

The steps in preparing a solution are calculated, weighed, dissolved, labeled and stored. First, the mass of the solute and solvent required is calculated, then weighed, and then the solute is dissolved into the solvent to prepare the solution, and finally the solution is filled into a reagent bottle and labeled.

In chemistry, the process of preparing a solution with chemicals and solvents (usually water) to the concentration required for the experiment is called preparing a solution. Before preparing the solution, you need to calculate the amount of items needed and clean the instrument. The preparation of solutions is divided into the preparation of solutions with solids, the preparation of solutions with liquids, and the preparation of solutions with gases.

There are a total of seven steps, respectively, Changxin is:

1) Calculation: Calculate the mass of the solid solute or the volume of the liquid concentrated solution required for preparation.

2) Weighing: Weigh the solid mass with a tray balance or measure the volume of the liquid with a graduated cylinder (a pipette should be used, but a graduated cylinder is generally used in secondary school).

3) Dissolving: dissolve or dilute the dissolution in a beaker and return to room temperature (if it cannot be completed and fully dissolved, it can be heated appropriately). Check the volumetric flask for water leaks.

4) Transfer: Carefully transfer the cooled solution in the beaker along the glass rod into a certain volume of volumetric flask (the lower end of the glass rod should be below the scale mark of the volumetric flask).

5) Washing: Wash the beaker and glass rod 2 3 times with distilled water, and transfer the washing solution to the container, shake, so that the solution is mixed evenly.

6) Constant volume: When adding water to the volumetric flask to 1cm 2cm below the scale line, use the rubber head dropper to add water instead, so that the concave surface of the solution is just tangent to the scale mark.

7) Shake well: Cover the cork, press the cork with your index finger, hold the bottom of the bottle with the fingers of the other hand, and turn it upside down repeatedly to mix the solution evenly.

8) Bottling labels.

1. Prepare with liquid reagent:

According to the principle of equality of solute mass before and after dilution, the formula is obtained:

1ρ1 v1= ω2ρ2 v2

1: Dilution concentration 1: Density v1: volume of solution to be dispensed.

2: Concentration of concentrated solution 2: Density v2: Volume of concentrated solution is required.

For example: To prepare 1000ml of 20% sulfuric acid solution, how many milliliters of 96% concentrated sulfuric acid are needed?

Look up the table and know: 1=when 20%; 2=at 96%.

Substitution formula: 20%.

v2= ×

Second, the preparation of the quantity and concentration solution of the substance.

1. According to the principle of the quantity and phase justification of the solute before and after dilution, the formula is obtained

c1v1=c2v2

C1: Concentration before dilution v1: Volume before dilution.

C2: Diluted concentration v2: Diluted volume.

For example, 500ml of concentrated sulfuric acid is prepared with 18mol l, and 3mol l of dilute sulfuric acid is required.

Substitution formula: C1V1=C2V2=18mol L V1=3mol L 500ml

V1 = 3mol l 500ml 18mol l = take the sulfuric acid, pour an appropriate amount of water under constant stirring, and dilute it to 500ml after cooling.

2. Prepare with liquid reagent.

Formula: V1 D A%=C V M 1000 cases: 500ml of sulfuric acid solution to be prepared, the dosage.

The weight percentage concentration is 98%, and d = more sulfuric acid.

Less ml? m sulfuric acid =

Dai Bi quietly into the formula:

v1×v1=

Configure the solution for a certain amount of substance in the experimental procedure:

Calculation: Calculate the mass of the solid solute or the volume of the liquid solute according to the requirements. Weigh or measure:

Weigh the mass of the solid solute with a tray balance, and accurately measure the volume of the liquid solute with a graduated cylinder. Dissolved or diluted: Solid solutes are dissolved in a beaker and liquids are diluted in a beaker.

Transfer: Cool the dissolved solution to room temperature and inject a volumetric flask of the desired volume along the glass rod. Washing: Rinse the glass rod and beaker 2 3 times with a small amount of distilled water, and pour the solution after each wash into the volumetric flask to ensure that all the solutes are injected into the volumetric flask.

Volume: Continue to inject distilled water into the above-mentioned volumetric flask to 2 3 cm away from the scale mark, and use a rubber tip dropper to add distilled water drop by drop, until the lowest point of the concave liquid level is tangent to the scale mark. Shake well:

Cover the volumetric bottle and shake it upside down. Bottling: Transfer the prepared solution to a clean reagent bottle, label it and store it in the designated location or set aside.

Configure the solution with a certain amount of substance, and pay attention to the closure matters

1. Experimental design.

Determine the desired solution concentration and preparation amount. Make sure you understand the experimental requirements and make calculations based on the required solute concentration to determine the required solute mass or solution volume.

2. Experimental preparation.

Before starting the experiment, prepare the required lab utensils and chemicals. Make sure lab utensils (e.g., volumetric flasks, beakers) are clean and free of impurities, and calibrate the scale of the measuring cup or volumetric flask.

3. Security measures.

Make sure you are familiar with safe operating procedures and laboratory safety measures before conducting experiments. Wear appropriate personal protective equipment such as lab gloves, goggles, and lab coats.

4. Solution quality inspection.

Once the preparation is complete, check the quality of the solution. Measure and record important parameters such as concentration and pH as needed to ensure that the solution meets the experimental requirements.

5. Labeling and storage.

Clearly label the container with the solution name, concentration, date of preparation, and laboratory-related information. Store the solution in an appropriate container and label it as needed.

6. Clean-up and waste disposal.

After completing the experiment, ensure that the solution residue and waste are properly disposed of. Dump the waste liquid into the appropriate waste container according to the laboratory's regulations, and thoroughly wash and clean the containers and laboratory utensils used.