Problems with the burette

It is mainly due to potassium dichromate being a strong oxidizing agent

The potassium dichromate standard solution is not used every day, but there is a dropper specifically designed for it, and it seems there is no issue as mentioned by the original poster. Clean it thoroughly after each use and turn it upside down to drain.

From Baidu; please pay attention to the description of its properties. Potassium dichromate 【Chinese name】Potassium dichromate； Potassium bichromate 【English name】potassium bichromate; potassium dichromate 【Structure or molecular formula】 K2Cr2O7 【Relative molecular weight or atomic weight】294.18 【Density】Relative density 2.676 (25°C) 【Solubility】The solubility in water at 20°C is 12 grams. 　　【Melting Point (°C)】398 　　【Properties】 　　Orange-red trigonal crystals or needle-shaped crystals. 　　【Solubility】 Soluble in water, insoluble in ethanol. 　　【Use】 Used for the production of chromium alum. Matches, chromium pigments, and are also used for tanning leather, electroplating, organic synthesis, etc. 　　【Preparation or Source】 It can be prepared by a double displacement reaction between sodium dichromate and potassium chloride or potassium sulfate. 　　【Other】 Releases oxygen upon decomposition at high temperatures, and has strong oxidizing properties. 　　Potassium dichromate 　　(I) Physical and chemical properties and uses 　　Orange-red plate-like crystals; may catch fire when in contact with flammable materials. Specific gravity is 2.676. The melting point is 398°C; oxidation occurs above 500°C to produce chromic acid and chromium trioxide. This product is a highly versatile chromium compound, used in laboratory applications such as chromic acid mixtures and dichromate titrations. It is also employed in industrial processes for the production of chromates and dichromates, in organic synthesis, electroplating, as a preservative, in pigments and mordants, as well as in photography, printing, batteries, safety matches, and chemical abrasives. 　　(II) Toxicity The toxicity of hexavalent chromium is greater than that of trivalent chromium. Chromium is also a sensitizing agent; hexavalent chromium is irritating and corrosive, and chromium is a carcinogen. 　　(III) Effects of short-term excessive exposure Inhaling it can cause respiratory tract inflammation, asthma, and chromium ulcers. 　　(IV) Effects of long-term exposure Workers who are exposed repeatedly or over a long period to low concentrations of chromium compounds may develop chronic upper respiratory tract inflammation, chromic rhinitis, contact dermatitis; rashes often appear on exposed areas such as the face, neck, hands, and forearms. It can also cause damage to the liver and kidneys, as well as lead to changes in the blood system. The incubation period for lung cancer is 10–20 years. 　　(5) Fires and explosions Under normal conditions, it is not prone to explosion. 　　(VI) Chemical reactivity: Strong oxidizing property, slightly soluble in water. 　　(7) Personal protection 　　1. Exhaust ventilation should be used at the sides of the electroplating tanks in the electroplating workshop to remove chromic acid mist; acid mist suppressants can be used inside the tanks. 　　2. Special faucets should be installed in the workshop to allow for immediate rinsing of the skin and eyes. 　　3. Strengthen personal protection: Workers handling chromic acid and chromates must wear gloves and wash their hands thoroughly. Before starting work, check for any injuries to the hands and skin, apply ointment to protect the nasal cavity, and rinse the nasal cavity after work. 　　4. Health monitoring: once a year. 　　5. Contraindications for employment: bronchial asthma, dermatitis. 　　(8) First aid 　1. In the event of inhalation of large amounts of chromic acid or chromates, move the affected person to a place with fresh air immediately, keep the respiratory tract unobstructed, and provide oxygen. 　　2. In the event of skin contact with chromic acid or chromates, the affected area should be immediately washed with clean water. 　　3. In case of oral poisoning, perform gastric lavage; administer 60 ml of 50% magnesium sulfate as a laxative, and give milk and egg white to protect the gastric mucosa. 　　(IX) Storage and Transportation 　It should be stored in a cool and dry place, with the containers kept sealed to prevent moisture absorption. Store and transport separately from organic substances, flammable materials, reducing agents, oxidizable substances, and acids. 　　(X) Safety and Handling 　1. Exhaust fans should be installed beside the plating tanks in the plating workshop to remove chromic acid mist; acid mist control agents can be used inside the tanks. 　　2. Special faucets should be installed in the workshop to allow for immediate rinsing of the skin and eyes. 　　3. Strengthen personal protection. 　　4. Health monitoring, pre-employment physical examination. 　　CAS No.: 7778-50-9 Potassium dichromate. It has extremely low solubility at low temperatures and does not contain crystalline water, making it easy to purify through recrystallization ； It is also resistant to deliquescence, and therefore is commonly used as a standard in analysis. 　　Applications and some reactions: Since potassium dichromate has strong oxidizing properties in acidic conditions, it is commonly used in the laboratory to prepare chromic acid washes (a mixture of a saturated solution of potassium dichromate and concentrated sulfuric acid) for cleaning chemical glassware, in order to remove reducing contaminants from the walls of the vessels. After use, the solution changes from dark red to green, at which point it becomes ineffective. 　　Potassium dichromate is also used in analytical chemistry, often to quantitatively determine reducing substances such as hydrosulfuric acid, sulfurous acid, and ferrous ions. 　　When heated, potassium dichromate can also oxidize concentrated hydrochloric acid, releasing chlorine gas. 　　Change in chemical equilibrium: When acid is added to a chromate solution, the color of the solution changes from yellow to orange, indicating that chromate ions are converted into dichromate ions. Conversely, when base is added to a dichromate solution, the color changes back from orange to yellow, meaning that dichromate ions are transformed back into chromate ions.

Due to its strong oxidizing properties in acidic conditions, potassium dichromate is commonly used in laboratories to prepare chromic acid washes (a mixture of a saturated solution of potassium dichromate and concentrated sulfuric acid) for cleaning chemical glassware, in order to remove reducing contaminants from the walls of the vessels. After use, the solution changes from dark red to green, at which point it becomes ineffective.

Since our potassium dichromate standard solution is used frequently, it is washed before it runs out. That would be even more troublesome. This phenomenon was not observed in other standard solutions. It takes a long time before it gets dirty. It’s just that the potassium dichromate standard solution is very dirty.

Hehe, it gets dirty quite easily. In our laboratory, we use pipettes to transfer the potassium dichromate standard solution; after transferring it, we clean the pipettes, but residue still remains inside them. There’s no way. :L