Preparation and Calibration of Potassium Dichromate Standard Solution: Playing with the "Little Orange Devil", Are You Ready?
Who is the most like a "rose with thorns" in the lab?potassium dichromateDefinitely on the list. This guy is pretty good-looking, orange-red crystal, shining in the sun, but if you are really deceived by its "beauty", it is not far from "rollover". Let's talk todayPreparation and Calibration of Potassium Dichromate Standard Solution, have a good fight with this hot-tempered "orange-red little devil".
Find out its "details" first: the physical and chemical ID card of potassium dichromate
Before taking action, you have to find out its temper. Know yourself and know your enemy, a hundred battles are not in danger.
| attribute | specific parameters | Remarks |
|---|---|---|
| Chinese name/alias | Potassium dichromate/potassium alum- | |
| English name | Potassium dichromate | |
| CAS number | 7778-50-9 | The world's only "ID number" |
| molecular formula | K₂Cr₂O₇ | |
| molecular weight | 294.18 | Key data for calculating concentration |
| appearance | Orange-red triclinic crystal | The appearance is online, but "ruthless" |
| density | 2.676 g/cm³ | Heavier than water |
| melting point | 398℃- | The melting point is quite high, don't think about melting it by heat |
| Boiling Point | 500 ° C (decomposition) | It decomposes before it reaches the boiling point |
| solubility | Soluble in water (slightly slower in cold water, faster in hot water)-, insoluble in ethanol- | When mixing solutions, it is better to use hot water to help dissolve |
| Aqueous solution properties | It's acidic. | |
| chemical properties | strong oxidation | This is its "killer" and it is also the basis of the application |
In addition, this guy's taste is a little "bitter" and has a metallic taste. Most importantly, it hasToxicand iscarcinogen, which is a "key object of concern" among hazardous chemicals. When operating, you must wear gloves and goggles and do it in a fume hood-。
Preparation and Calibration: A Game of "Direct" and "Indirect"
It is precisely because of the stability and high purity of potassium dichromate that it can becomereference substance-This means that, in theory, we can directly prepare its standard solution
Direct preparation method (worry-free mode) The operation is simple: put the reference potassium dichromate in150～180℃drying2 hours, put it in a dryer to cool. Then accurately weigh a certain amount (for example, to prepare 0.1mol/L, about 4.9g needs to be weighed), dissolve it with distilled water, and put it in a volumetric bottle for bandwidth evaluation-The solution prepared in this wayNo calibration requiredIt can be used directly.
But why are we always talking aboutPreparation and Calibration of Potassium Dichromate Standard SolutionWoolen cloth? Because in actual operation, we may not use a benchmark reagent with 100% purity, or have extreme requirements for concentration accuracy. Then you need toIndirect preparation method (calibration mode) Usually weigh about5gChemically pure potassium dichromate, soluble in1000mLWater, shake well and leave for a day, then useiodometryPerform calibration-。
The specific operations are as follows: accurately measure the prepared potassium dichromate solution20mL-Put it in an iodine flask and add10%~ 15% potassium iodide solution-, place in the dark after plugging3-10 minutes-Then, with the calibratedSodium Thiosulfate Standard Solutiontitration-Titration until the solution isyellow-greenWhen joiningStarch indicatorContinue to titrate untilThe blue disappears, the solution turns bright greenThat is the end point.
The whole process was like a game of "traffic lights", from orange-red to yellow-green to bright green, the colors changed and changed, and if you were not careful, you would be confused. At this time, a good "off-site guidance" is very important.
Scientific Grain Officer: Your experiment "Logistics Minister"
Preparing and calibrating potassium dichromate solutions requires a lot of effort every step of the way, from drying benchmarks to dark reactions. At this time, reliable reagents and consumables are half the battle.Scientific Grain Officer- The one-stop shopping platform for the intelligence of scientific materials is the "logistics minister" on your bench. "Intelligent manufacturing is only standard, and the experiment is not too embarrassing". The platform has a database of over 10 million fine chemicals, from benchmark potassium dichromate to sodium thiosulfate, potassium iodide, and starch indicators, so you don't have to pay for it in one stop.Preparation and Calibration of Potassium Dichromate Standard SolutionPiece it together, and don't worry about the results being biased due to insufficient reagent purity.
Frequently Asked Questions (FAQ)
- Q: How long can I keep the potassium dichromate solution after it is prepared?
- A: The potassium dichromate solution prepared with the reference reagent is relatively stable and can be stored in a closed and cool place for a long time. However, it is recommended to check regularly. If turbidity or precipitation is found, it should be reformulated.
- Q: Why use hot water when preparing?
- A: Potassium dichromate dissolves slowly in cold water, but hot water can accelerate the dissolution and improve the preparation efficiency.
- Q: Why is it placed in the dark during calibration?
- A: This is to ensure that the reaction between potassium dichromate and potassium iodide is complete -. Iodine ions are easily oxidized by oxygen in the air under acidic conditions, and placing them in a dark place can reduce this interference.
- Q: Why is the titration endpoint bright green instead of colorless?
- A: This is because trivalent chromium ions (Cr ³) are formed in the solution, and the aqueous solution itself appears green-3. This color is a sign of the completion of the reaction, not the color of the indicator.
Scientific Grain OfficerWell said: "The troops have not moved, the grain and grass go first". The rigor of the experiment starts with the quality of each bottle of reagent. Hope next time you facePreparation and Calibration of Potassium Dichromate Standard SolutionWhen I can think of this strategy, there is less hustle and bustle and more calmness. After all, experiments can be rigorous, but the mentality must be relaxed - this is what science should be like.
