Thread Content
Points to note when using glassware 1. Washing of glassware 1.1 Newly purchased glassware often has free alkaline substances on its surface; it can be first washed with a 0.5% detergent, then rinsed with tap water. After that, it should be soaked in a 1%~2% hydrochloric acid solution for overnight (at least four hours), followed by rinsing with tap water. Finally, it should be washed two to three times with deionized water and placed upside down on a rack for later use. 1.2 For used instruments, first wash them with tap water until no dirt remains, then clean them with detergent powder or solution, rinse again with tap water, and finally wash them with deionized water two to three times. Place them upside down on a rack for later use. The standard for cleanliness is that there should be no water droplets on the inside or outside of the utensil, with a thin layer of water evenly covering its inner surface. 2 Use of the burette 2.1 The methods for checking for leaks and cleaning are omitted. 2.2 When filling it with a standard solution, do not use a funnel or any other container to avoid changes in the concentration of the standard solution or contamination. 2.3 Reading: Wait for 0.5 min to 1 min before and after titration for the solution adhering to the inner wall to flow down before taking a reading; if the titration rate is fast, the waiting time can be appropriately extended (1 min to 2 min). 2.4 Calibration: Volume calibration and temperature calibration. It is required to be able to read volume calibration charts and use temperature calibration formulas. 2.5 Specifications: Select the appropriate burette based on the amount of solution used in titration. 2.6 After use, the burette should be washed thoroughly and placed upside down on the burette stand to prevent the solution from corroding the inner wall of the burette. 3 Use of volumetric flasks 3.1 Methods for checking for leaks and cleaning are omitted. 3.2 Procedures for preparing solutions and adjusting their volume are omitted. 3.3 Volumetric flasks are precision measuring instruments; they should not be used to store solutions for long periods of time. In particular, alkaline solutions can erode the walls of the flask and cause the stopper to stick and become unable to be removed. After use, they should be washed thoroughly with water and dried before being stored for future use. 3.4 During operation, do not hold the bottle body with your hands, to prevent the liquid from expanding due to body heat and affecting accuracy. 4 Use of pipettes 4.1 Leak testing, washing, and pipetting are omitted. 4.2 Drying: Before rinsing, blow away any remaining water from the tip, and use filter paper to dry the water droplets on the outer surface of the tip. 4.3 Rinsing: Before formally transferring the sample solution, rinse it 3 times, being careful not to allow the solution to flow back; let it drain from the lower opening. 4.4 Draining: The pipette should be held vertically, with its tip against the wall; the pipette body should form an angle of about 30° with the wall of the container. Do not blow using your mouth or a bulb, unless it is indicated that blowing is allowed. After all the liquid has drained, wait for 15 seconds. 5 Use of the dryer 5.1 Greasing, switching on/off, and moving the dryer. 5.2 The weighing flask must reach a constant weight, and it should be kept in the desiccator for the same amount of time. 6 significant figures are required. 6.1 Round off by rounding to the nearest even number. 6.2 For addition and subtraction operations, the value with the largest absolute error among all the data involved (i.e., the one with the fewest decimal places) should be used as the standard. 12.38+0.006=12.39. In multiplication and division operations involving 6.3, the value with the greatest relative error (i.e., the fewest significant figures) among all the values involved should be used as the standard. 6.4 Calculation of significant figures: If the first digit is 8 or greater, one additional significant figure should be counted. 6.5 Simple counts, fractions, or multiples are exact numbers or natural numbers, and their number of significant figures is infinite. For example, 16.60/6=2.767