An evaporating dish is a shallow, heat-resistant ceramic or glass vessel used in laboratories to evaporate solvents and concentrate solutions.
It is commonly used in crystallization, drying samples, and removing excess liquid from chemical mixtures.
The dish’s wide, open surface area allows for faster evaporation, while its high heat resistance enables it to withstand direct heating from a Bunsen burner or hot plate.
Evaporating dishes are essential in qualitative and analytical chemistry for preparing solid residues from liquid solutions.
Types of Evaporating Dishes
There are several types of evaporating dishes, each designed for specific laboratory applications based on material, shape, and heat resistance.
1. Ceramic Evaporating Dish
- Description: Made from porcelain or alumina, these dishes are highly heat-resistant and can withstand direct heating from a Bunsen burner.
- Uses: Ideal for high-temperature evaporation, crystallization, and drying solid residues from solutions.
2. Glass Evaporating Dish
- Description: Typically made of borosilicate glass (e.g., Pyrex), offering good heat resistance but less durability under extreme heat compared to ceramic.
- Uses: Used for gentle evaporation, especially in experiments requiring visibility of the liquid as it evaporates.
3. Shallow (Low-Form) Evaporating Dish
- Description: A wide, shallow dish that increases the surface area for faster evaporation.
- Uses: Common in analytical chemistry for quick concentration of solutions and crystallization experiments.
4. Deep (High-Form) Evaporating Dish
- Description: A deeper dish with higher walls, reducing the risk of splattering during evaporation.
- Uses: Suitable for larger volumes of liquid or reactions prone to bubbling.
5. Evaporating Dish with Spout
- Description: A dish with a small pouring spout, making it easier to transfer concentrated solutions or solid residues.
- Uses: Helpful in precise liquid handling and transferring crystallized substances.
Uses of an Evaporating Dish in the Laboratory
The evaporating dish is a versatile laboratory tool with many important applications, particularly in processes involving heating, drying, and concentration of substances. Here are some of its key uses:
- Evaporation of Solvents – Used to remove excess liquid from solutions, leaving behind solid residues or concentrated substances.
- Crystallization – Helps in the formation of crystals by slowly evaporating the solvent from a saturated solution.
- Drying of Samples – Used to dry chemical samples by gently heating them to remove moisture.
- Concentration of Solutions – Allows for the reduction of liquid volume to concentrate the solute in a solution.
- Heating Stable Substances – Suitable for direct heating of heat-resistant substances over a Bunsen burner or hot plate.
- Precipitate Separation – Used to evaporate liquid and isolate precipitates in qualitative analysis.
- Ash Content Determination – In analytical chemistry, it helps determine ash content by burning organic material and analyzing the remaining residue.
- Chemical Reactions Requiring Evaporation – Used in reactions where solvent evaporation is necessary to drive a chemical process.
- Food and Beverage Analysis – In food chemistry, it assists in testing the solid content of liquids like milk or juice by evaporating water.
Safety Precautions
When handling hot evaporating dishes, it is crucial to use tongs or heat-resistant gloves to prevent burns and ensure safe transfer.
Direct contact with a hot dish can cause severe injuries, especially in high-temperature experiments.
Additionally, even heating is essential to avoid thermal shock, which can lead to cracks or breakage.
Sudden temperature changes, such as placing a hot dish on a cold surface or heating it too quickly, can weaken the material and cause failure.
After evaporation, proper disposal of chemicals is necessary to maintain a safe lab environment.
Residues left in the dish should be disposed of according to laboratory waste protocols, ensuring that harmful or reactive substances do not contaminate workspaces or water systems.
Cleaning and Maintenance
To extend the lifespan of an evaporating dish, regular cleaning is essential.
After each use, ceramic and glass dishes should be rinsed with distilled water and cleaned with a mild detergent to remove residual substances.
For stubborn residues left behind from chemical reactions, soaking the dish in an appropriate solvent or using a gentle abrasive scrub can help restore its surface without damaging it.
Once clean, proper storage is crucial to prevent breakage. Evaporating dishes should be kept in a designated storage area, preferably stacked with protective padding or separated to avoid chipping.
Handling them carefully and avoiding unnecessary impact ensures their durability for repeated use in laboratory experiments.
