Question 1: Why does the standard solution of sodium hydroxide need to be calibrated with a reference material after being prepared?
The prepared solution is a preliminary content, and the concentration value has not yet reached the real value. In order to make the concentration of the titrant closer to the real value, it needs to be calibrated with a reference substance.
In addition, because sodium hydroxide is easy to deliquescence in the air, errors are prone to occur in the process of weighing the solid sodium hydroxide and configuring the sodium hydroxide solution.
Question 2: What should be paid attention to when calibrating sodium hydroxide standard solution
The first step: when preparing a saturated sodium hydroxide solution, weigh 110 grams of sodium hydroxide, dissolve it in 100 ml of carbon dioxide-free water, stir as it is added, and shake it up to complete the dissolution. In the reagent bottle, seal it with a rubber stopper, and let it stand for more than 7 days to make the sodium carbonate precipitation completely. Take a little clear saturated sodium hydroxide solution, dilute with water, add 1 ml of saturated barium hydroxide solution, no turbidity occurs within ten minutes, indicating that the sodium carbonate has been completely precipitated.
In this way, the saturated liquid that meets the requirements can be obtained! This is also the first step in formulating a good standard solution of sodium hydroxide!
Step 2: Prepare the solution: Take 0.1mol/L as an example, the standard stipulates that 5.4 ml of saturated solution needs to be drawn to prepare a 0.1mol/L solution. In view of the regulation that the error between the actual value of the standard solution and the specified value should be within 5%, it should be Absorb strictly as required. However, for some reasons, the factor of volume change may cause errors to prevent the standard solution of 0.09**** from sometimes appearing. We generally draw 5.6 ml to 1L of solution, (the final result is generally around 0.102)! After the preparation is complete, shake it well, and shake it after a period of time to ensure that the solution is uniform and stable! Usually every other day, the calibration is carried out!
Question: Sometimes the concentration of 0.09756 is inevitable, which will cause some unnecessary troubles, such as how many significant digits are there? The standard stipulates that 4 is reserved as a significant number, and the final result should be 0.0976 or 0.09756. (The first number at the beginning is 8 or 9 can be counted as a significant number)
And there are still some troubles for future calculations, so you should try to avoid such values!
Step 3: Calibration.
Potassium hydrogen phthalate must be thoroughly dried, and it must be shaken several times during the drying process of the oven. The bottom medicine can also be thoroughly dried!
In the weighing process, use the weight reduction method, practice more, and try to reduce the number of repetitions based on experience. Weigh the specified quality at the least number of times, no more than three times at most, and it is best to do it at one time!
Weigh the quality should try to ensure that the volume of the consumed solution is 30-40 ml, and try to reduce the volume error!
During the calibration process, the speed should be well controlled, and the parallel samples should be as consistent as possible!
