Tech II Exam 1 Scaffolding

• 1. State the proper waste disposal method for the following materials.
  2. Paper towels from washing hands - may go in regular trash
  3. Used silica gel TLC plates - Hazardous solid waste
  4. Chloroform - Halogenated waste
  5. Solid sodium hydroxide/Concentrated sulfuric acid - Dissolve and neutralize to pH between 4 and 10. Put in Aqueous waste if there may be organic residues.
  6. Acetone from washing glassware - Acetone waste or nonhalogenated waste
• 2. Identify the hazard(s), for the following common solvents and chemicals. What is the appropriate response?

  1. Acetic acid, CH3COOH

  Corrosive, vapors are irritants to mucous membranes. In case of contact, wash skin or eyes thoroughly.

  1. Acetone Flammable, always work in hood.
  2. Chloroform, CHCl3 Acutely toxic, Potential carcinogen. Always work in hood. Clean up spills promptly.
  3. Silica gel TLC plates Solid waste
• Describe the distillation method for measuring boiling point:

  the temperature seen at the distillation head during active distillation provides an estimate of the boiling point of the distilling liquid.
• During a distillation, even though the flask is being heated, no temperature change was seen at the thermometer for almost ten minutes. Then the temperature suddenly shot up to 95°C. Why?

  Vapors have much lower heat capacity than liquids. Even though the vapors are getting warmer as the flask is heated, the thermometer won’t register a change until the vapors begin to condense on the bulb. This will happen at about the same time and the vapors begin to condense in the condenser.
• Assembly of Semi-microscale method of measuring BP: About 1 mL of liquid is placed in a small test tube with an inverted melting point capillary (open end down). A thermometer is attached to the outside of the test tube with a rubber band, and the assembly is lowered into an oil bath, keeping the rubber band above the level of the oil.
• Measuring BP using Semi-microscale method: The oil bath is heated slowly until a rapid and continuous stream of bubbles is exiting the capillary tube. Heating is stopped. When the stream of bubbles stop, record the temperature, and when the liquid just begins to back up into the capillary, record this temperature (they may be the same). This gives the boiling point, at which point the vapor pressure of the liquid equals the ambient pressure (the definition of boiling point).
• In distillation, why is it important that the water goes in at the lower end of the condenser and out at the upper end?

  This allows the entire condenser to be filled with cooling water and maximized the efficiency of condensation.
• What might cause the observed boiling point to be lower than the true literature value?

  This can occur if the thermometer bulb is too high in the distillation head, such that it does not get completely coated in condensing liquid. It can also happen if the distillation head is not well-insulated, leading to heat loss through the glass walls, or if there is not very much liquid to distill, such that the thermometer bulb cannot be coated.
• What is the appropriate level for the thermometer bulb in the distillation head?

  The top of the bulb should be at the bottom of the side-arm, so that the bulb can be coated in condensing liquid. If placed higher, the condensing liquid will run out the condenser without coating the thermometer.