The correct way to use the graduated cylinder in glassware
One: measuring cylinder
common problem:
A. Hold the measuring cylinder in hand to read; B. When reading, some look down, some look up;
c. Some measuring cylinders cannot be selected according to the required liquid volume. D. Add more liquid, and use the dropper to suck out.
Correct method: When using a measuring cylinder, you should select a small-sized measuring cylinder that can be measured at one time according to the volume of the liquid to be measured.
The operation essentials are "measure the liquid, the cylinder is stable; the mouth is mouth to mouth, avoid outflow; change the drip to the scale; when reading, keep the line of sight and the low level of the liquid level".
If the amount of liquid added accidentally exceeds the scale, you should hold the graduated cylinder and pour a small amount into the designated container, and then drop it to the scale with a dropper.
Two: volumetric flask
common problem:
A. Do not test for leaks or wash the volumetric flask in advance; in the preparation of standard solutions, some students hold the volumetric flask with their hands to prevent the flask from falling.
Correct method: The volumetric flask should be checked for water leakage before use.
The method is as follows: add tap water to the vicinity of the marking line, cover the bottle stopper, press the stopper with the index finger, and hold the part above the marking line of the bottle neck with other fingers,
Hold the bottom of the bottle with your fingertips with the other hand, and stand upside down for two minutes. If there is no leakage, put the bottle upright, rotate the stopper 180 degrees, and try again.
If the volumetric flask and stopper are stained, the washing method is similar to that of the burette.
If it is not clean with tap water, it can be soaked in the lotion, then rinse the bottle with tap water, and then wash it three times with distilled water.
When setting the volume, do not hold the volumetric flask by hand to prevent the glass from expanding due to heat, which will affect the volume of the volumetric flask, thereby affecting the concentration of the solution.
B, Transfer the uncooled solution into a volumetric flask; the solute transfer is incomplete.
Correct method: When preparing a standard solution in a volumetric flask, if it is a solid substance, it should be dissolved in a small beaker first, and then the solution should be transferred to the volumetric flask.
To transfer all the solutes into the volumetric flask, it should be: the beaker mouth is close to the glass rod extending into the volumetric flask, the upper part of the glass is not against the bottle mouth, and the lower end is against the bottle wall.
But do not use force, let the solution flow into the bottle along the glass rod. After the solution flows in, move the beaker up along the glass rod and stand upright, and then the glass rod moves up along the bottle wall.
Take it out and put it back into the beaker, rinse the glass rod and beaker with the washing bottle, press the glass rod with the tiger's mouth, grasp the beaker bottle mouth with five fingers, wash the bottle first, wash the glass rod, and then rinse around the beaker.
Transfer the solution to a volumetric flask in the same way and repeat two to three times until washed.
For the preparation of standard solutions with liquids, attention should also be paid to thermal effects, and other operating steps are also similar to the preparation of solutions with solid substances.