What are the precautions for liquid-liquid extraction?

Anyone who has studied chemistry must be familiar with the term extraction. Extraction can also be called liquid-liquid extraction, or extraction. This extraction method has many advantages, such as being able to save energy to the greatest extent and being very convenient to operate. To this day, liquid-liquid extraction has been widely used in many fields. So what should we pay attention to when doing liquid-liquid extraction?

Liquid-liquid extraction precautions:

1. Check for leakage before use

2. When shaking, hold the separatory funnel with both hands, press the stopper with your right hand, lay it flat, and shake it up and down

3. Open the bottle stopper before draining

4. When discharging liquid, remember that the lower layer is the liquid with high density, so discharge it from the bottom. The upper layer is the liquid with relatively low density, so pour it from the top.

5. Clean immediately after use

The instability you are talking about refers to the instability of the photometer readings during the measurement process? Or are the values ​​measured for several samples of the same type very different?

If it is the former, it is probably a problem with the instrument. If it is the latter, it may be that the oscillation is not sufficient during the extraction process, or the solution is left standing for too long after separation, resulting in different arsenic contents in different parts of the solution. Therefore, the measurement should be carried out immediately after sufficient oscillation to avoid similar situations.

Because the substance being measured is a trace amount, a small deviation in arsenic content will greatly affect the measurement result, so it is necessary to pay attention to

1. Precautions for using the spherical separatory funnel:

1) Before use, the glass piston should be coated with a thin layer of vaseline, but not too much to avoid blocking the flow hole. When using, hold the funnel ball with the base of your left hand and use your thumb and index finger to turn the piston to control the addition of liquid. At this time, the small groove of the glass piston must be aligned with the small hole on the side of the funnel mouth to ensure smooth liquid addition.

2) When used as a liquid adder, the lower end of the funnel cannot be immersed below the liquid surface.

2. Precautions for using the pear-shaped separatory funnel:

① Check whether the separatory funnel is leaking;

② Pour the mixed liquid into the separatory funnel and place the separatory funnel on the iron ring.

③Open the piston of the separating funnel, then open the stopcock to release the lower layer of liquid (water) from the lower end of the separating funnel. When the oil-water interface is tangent to the upper end of the stopcock, close the stopcock;

④ Pour out the upper liquid (oil) from the top of the separatory funnel.

Note: If using a pear-shaped separatory funnel for extraction: during oscillation, the small groove of the piston should be offset and tightly sealed with the small hole on the side of the funnel mouth. When separating the liquid, the lower layer of liquid flows out from the neck of the funnel, and the upper layer of liquid should be poured out from the mouth of the funnel.

Note: After cleaning the separatory funnel, take out the stopper and do not insert it into the separatory funnel, especially before entering the oven; when the separatory funnel is not used for a long time, a piece of paper should be clamped on the piston surface to prevent sticking. And use a rubber band to cover the piston to prevent it from falling.