Experimental principles of chemical solution preparation, 1 Experimental principle of NaCl solution

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.

Experimental principle: C=N V (mol L) C: Concentration N: Amount of substance V: Volume of solution.

Experimental operation procedure:

1.Calculation: n=m m, c=n v, p=m v

Example: The laboratory prepares 250ml of hydrochloric acid solution with concentrated hydrochloric acid with a density of concentrated hydrochloric acid and a mass fraction.

v=m/p=(

2.Weighing or measuring: Solid reagents are weighed with an analytical or electronic balance (to match the accuracy of the volumetric flask), and liquid reagents are weighed with a graduated cylinder.

3.Dissolve: Put the weighed solid into a beaker and dissolve it with an appropriate amount (20 30 ml) of distilled water.

4.Rewarming: Wait for the solution to cool and move into a volumetric flask.

5.Transfer (pipetting): Due to the thin neck of the volumetric flask, in order to avoid the liquid from spilling outside, drain with a glass rod, the glass rod can not be close to the mouth of the volumetric flask, and the bottom of the rod should be against the scale line of the wall of the volumetric flask.

6.Washing: Wash the inner wall of the beaker 2 3 times with a small amount of distilled water, and transfer all the washing liquid to the volumetric flask.

7.Primary mixing: Gently shake the volumetric flask to mix the solution evenly.

8.Constant volume: Add distilled water to the volumetric flask, and when the liquid level is 1 2cm below the scale line of the capacity bottleneck, use a rubber head dropper to add distilled water dropwise until the liquid level is tangent to the scale mark.

9.Shake well, cover the cork and turn it upside down repeatedly, shake well, if the liquid level drops, do not add water to set the volume.

10.Since the volumetric flask cannot hold the solution for a long time, the prepared solution is transferred to the reagent bottle and labeled.

Precautions. 1.Sodium hydroxide is an alkaline chemical, concentrated hydrochloric acid is an acidic chemical, be careful not to splash on your hands and body to avoid corrosion, and it is best to wear protective glasses during the experiment.

Once sodium hydroxide is accidentally splashed on your hands and body, rinse with more water and then apply a boric acid solution. When weighing, use a beaker to place.

2.Pay attention to the accuracy of the calculations.

3.Pay attention to the use of pipettes.

4.To dilute concentrated sulfuric acid, acid is slowly injected into water along the wall of the vessel and stirred continuously with a glass rod.

5.The prepared solution should be loaded into the reagent bottle in time, corked and labeled (the label should include the name of the drug and the mass fraction (or molar fraction) of the solute in the solution), and put it in the corresponding reagent cabinet.

(1) Calculation example: the mass of sodium chloride is 50 g 1 = g, and the mass of water is 50 g - i.e. the volume of water is.

The calculation is based on solute mass = solution mass solute mass fraction, solvent mass = solution mass - solute mass, and the volume of solvent can be converted according to the density formula.

2) Weigh sodium chloride.

Precautions: Before weighing dry solids, a piece of paper of the same quality should be placed on each of the two trays, and then the drug should be weighed on the paper, and the drug that is easily deliquescent (such as sodium hydroxide) must be weighed in glassware (such as a small beaker, surface dish). When weighing, the weight and the weight of the free plate should be fixed first, and then the solid reagent should be added to the left plate.

When the balance is close to equilibrium, hold the spoon in one hand and gently tap the wrist holding the spoon with the other hand to add a small amount of medicine until the balance is balanced.

3) Measure the amount of water you take.

Note: According to the volume of water, select a graduated cylinder with a volume of 50 ml (the principle of measuring cylinder selection: "large and close").

During the addition of liquid, when the scale of the liquid level is close to ml, the dropper is used to add dropwise until the liquid level is reached. The reading should be at eye level with the lowest part of the liquid concave level.

4) Dissolve: Stir with a glass rod to dissolve all the sodium chloride.

Note: Dissolution must be carried out in a beaker, and the solution cannot be prepared in a graduated cylinder.

5) Transfer: Put the prepared sodium chloride solution into a fine-mouth bottle, close the bottle and label it, and put it in the reagent cabinet.

There are three types of preparation solutions:

The first case is the preparation of a solution from a solid;

The second case is the preparation of a solution with a liquid;

The third case is the preparation of a solution with gas.

In junior high school, you only need to master the preparation of the first two solutions.

Example 1: Experimental procedure for preparing 100 grams of sodium chloride solution with a mass fraction of 10% with a clear shirt:

1. Calculation. Prepare 100 g of sodium chloride solution with 10% mass fraction.

The mass of sodium chloride required = 100g * 10% = 10 grams, the mass of the required water backup cavity = 100g - 10g = 90g, and the volume of required water = 90g (1g ml) = 90ml

2. Weighing. Weigh 10 g of sodium chloride on a tray balance and pour into a beaker.

3. Dissolve. Measure 90 ml of water with a graduated cylinder, pour it into a beaker containing sodium chloride, and stir with a glass rod to dissolve the sodium chloride.

4. Labeling and storage.

Put the prepared solution into the reagent bottle and label it (the label should include the name of the drug and the mass fraction of the solute in the solution), and put it in the reagent cabinet.

Example 2: Protocol procedure for preparing 500 g of dilute sulfuric acid with 98% mass fraction of concentrated sulfuric acid (p = 20% mass fraction:

1. Calculation. The preparation of 500 grams of dilute sulfuric acid with a mass fraction of 20% requires the mass of concentrated sulfuric acid = (500g * 20%) 98% = 102g

Volume of concentrated sulfuric acid required = 102g

The quality of the required water = 500g - 102g = 398g

Volume of water required = 398g (1g ml) = 398ml

2. Measure (this step is different from the solid preparation solution).

Measure 398ml of water with a graduated cylinder and pour it into a beaker.

3. Dilution (this spring step is also different from the solid preparation solution).

Measure milliliters of concentrated sulfuric acid with a graduated cylinder, slowly inject water along the wall of the beaker, and stir continuously with a glass rod to make the heat generated spread rapidly.

4. Labeling and storage.

After cooling, the prepared solution is put into the reagent bottle and labeled (the label should include the name of the drug and the mass fraction of the solute in the solution), and put it in the reagent cabinet.

The steps to prepare the solution vary depending on the solution being configured. Here are two examples:

Example 1: Steps to configure, 400 ml NaOH solution:

To accurately configure the concentration of sodium hydroxide, it is necessary to use a volumetric flask to determine the volume. If there is no 400 ml volumetric flask in the laboratory, a 500 ml volumetric flask is used.

1. Calculate the mass of sodium hydroxide that is required.

g 2, weigh grams of sodium hydroxide in a beaker, add a small amount of water to dissolve, then pour into a 500 ml volumetric flask, wash the beaker in 3 times, pour all the solution into the volumetric flask, and finally dilute it with water to the scale mark. Shake well, that is, the resulting sodium hydroxide solution.

If you don't need to be very accurate, you can directly use a graduated cylinder to measure 400 ml, and you only need to weigh grams when you weigh it.

Example 2: Steps to prepare 200ml of dilute sulfuric acid.

Part 1 calculation: According to C1V1=C2V2, calculate the volume of concentrated sulfuric acid required.

Step 2: Measure, using a straw to absorb the volume of concentrated sulfuric acid required.

Step 3: Dilution, transfer the concentrated sulfuric acid to a small beaker, dilute with a small amount of water, Step 4: Transfer, after the temperature of the solution is reduced, transfer the sulfuric acid in the beaker to a 200ml volumetric flask.

Step 5, wash, wash the small beaker, and the glass rod used when transferring, at least three times, and transfer the washing water to the volumetric flask.

Step 6: Fix the volume, add water to the scale mark, and use the rubber head dropper to fix the volume about one cm away from the scale mark.

Step 7: Shake well, shake the solution well, if the liquid level drops, do not add water to determine the volume.

Step 8: Transfer the prepared solution to the reagent bottle and label it.

The general process of solution preparation is as follows:

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

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

3.Dissolve: Dissolve or dilute the solute in a beaker and return to room temperature (if it cannot be completely 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 volumetric flask of a certain volume (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 into the container Wuchi hail, shake, so that the solution is mixed evenly.

6.Volume: When adding water to the volumetric flask to 1cm 2cm below the scale line, use the rubber tip dropper to add water instead, so that the concave surface of the solution is exactly 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. Finally, the prepared solution is poured into the reagent bottle and labeled.

Liquid solution preparation is arguably the most basic technique for laboratory analysts, and it is also a must in their daily work. The configuration of liquid solution includes basic operations such as solute calculation, pipetting, and volume determination, as well as the addition sequence of some mixed solutions and the use of some reagents' own chemical properties, and mastering the skills of solution preparation, which can greatly shorten the configuration time.

The solution chamber sail is composed of at least two substances.

1. A stable mixture in which the dispersed substance (solute) is dispersed in molecules or smaller particles in another substance (solvent). The solution is a mixture. The types are divided into: general solutions and standard solutions. Substances have three states at room temperature: solid, liquid, and gas.

Therefore, there are three states of solution, the atmosphere itself is a gaseous solution, and the solid solution mixture is often called a solid solution, such as an alloy. General solution simply refers specifically to liquid solution. There are two types of liquid solutions, namely electrolyte solutions that are capable of conducting electricity and non-electrolyte solutions that are not.