Physical Techniques of Drying

Physical Techniques

• Drying is the process of removing liquid (like water) from a material. It involves using heat and a sink to collect vapor. It's also used to remove water vapor from gases.
• Heated air drying uses a heated air stream to remove moisture. Higher temperatures speed up water removal, but too high a temperature can dehydrate the material too much, causing shrinking and internal pore closure, or crust formation. Air temperature must be controlled based on product quality.
• Natural air drying uses unheated air. It's slow and dependent on weather conditions (temperature, humidity, moisture content). This method often takes weeks or months.
• Indirect/contact drying (drum drying & vacuum drying) use heated surfaces to remove moisture. Drum drying involves a heated surface and aspiration for removing vapor. Vacuum drying uses contact conduction or radiation, pulling vapor with a vacuum system.
• Freeze drying (lyophilization) involves freezing the material first and then sublimating the solvent (converting it directly from solid to gas) at low temperatures and pressure. This process avoids structural collapse, leaving a porous product. It's used in preserving foods and vaccines.
• Supercritical drying uses steam. The water in the product is boiled off and combined with the drying medium, increasing the flow. This method recovers latent heat through recompression.
• Dielectric drying uses microwaves to remove moisture; it's currently under research. It can be used in conjunction with air or vacuum drying.

Grinding

• Grinding breaks down materials using compression, impact, attrition (wear and tear), or shear. This produces powdered substances by reducing the size of the materials.
• Mortar and pestle has been used throughout history for grinding and mixing substances. Mortar (the bowl) and pestle (the tool) are often made from hard woods, metal, or ceramics. Substances are crushed and mixed until the desired texture is reached.

Weighing

• Direct Weighing:
  • Set the scale to zero.
  • Place the container on the scale and set it to zero again.
  • Transfer the substance into the container using a clean scoopula until the desired mass is reached.
  • Record the mass.
• Indirect Weighing (Difference Method):
  • Weigh the container.
  • Transfer some of the substance to another container.
  • Weigh the container again.
  • Subtract the new mass from the original mass to get the transferred substance's mass.

Spectrophotometry

• A method for measuring how much a chemical substance absorbs light.

• Used in various fields like chemistry, physics, biochemistry, and clinical applications.

• Used to detect substance concentrations, impurities, organic compound structures, dissolved oxygen in water, and functional groups.

• Spectrophotometer: Measures the amount of photons that pass through a solution.

• UV-visible spectrophotometer: Measures light in the UV and visible ranges.

• IR spectrophotometer: Measures light in the infrared range.

Extraction

• A laboratory technique used to isolate a product from other substances.
• Types: solid-liquid, liquid-liquid, and acid-base extractions.
• Uses a separatory funnel. Extractions use two immiscible phases (phases that do not mix, like oil and water, to separate substance from one phase to another) to isolate a substance from a mixture.
• Useful in separating organic products from inorganic substances.
• Solvents are chosen with specific properties for the extraction to be achieved effectively (solubility, non-reactivity).

Titration

• A qualitative analysis technique to calculate the concentration of a substance in a mixture.
• Also known as titrimetry.
• Involves preparing a titrant (solution with a known volume and concentration) and reacting it with the analyte (substance to be analyzed). The process is continued until an equivalence point (the endpoint) is reached.
• Used in many applications like medicine, labs, and food analysis. The process involves finding out the exact volume of the titrant required to complete a reaction with the analyte.

General Lab Safety Rules

• Preparation: Understand the experiment and plan.
• Appropriate Protective Equipment: Wear safety guidelines like closed-toe shoes, hair tied back, and proper clothing.
• Responsibility in the lab: Follow procedures, don't touch or eat anything in the lab without instructor guidance or permission. Be careful when handling materials.
• Ask Questions: Ensure you understand the procedure and don't use lab equipment without instruction.
• Proper Chemical/Electrical Use: Read labels on containers twice, follow teacher's instructions for disposing of chemicals, and only take only what you need.
• Care and Attention: Don't touch (smell, taste, eat) anything, don't work alone, and carefully handle equipment, glassware, etc.
• Report Problems: Report any accidents; follow emergency procedures for injuries or spills.
• Keep Lab Area Clean: Don't bring food or drinks into the lab, and keep the lab clean.
• Unauthorized Experiments: Don't perform unapproved experiments.
• Emergency Procedures: Know where safety equipment is in case of emergencies (eye wash, fire extinguishers). Report any unsafe conditions.

This quiz covers various physical techniques used for drying materials, including heated air drying, natural air drying, and indirect/contact drying methods. You'll learn about the principles behind each technique, their advantages, disadvantages, and specific applications in different contexts.