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A Rotovap Quiz
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1. What conditions do you need to remove dimethylformamide (DMF)?
a. dry-ice condenser b. high-wattage water bath c. strong pump and tightly sealed system d. can’t be done with an evaporator
See why
Image Credit: Heidolph
Answer: C, strong pump and tightly-sealed system.
DMF has a higher boiling point than water at atmospheric pressure. In an 11 mbar atmosphere, it will evaporate at just 40C. To get a vacuum that strong, you need a strong pump and no air leaks.
a. dry ice condenser b. high-wattage water bath c. strong pump and tightly-sealed system d. can’t be done with an evaporator
See Why
References: MJLPHD, Heidolph.
Next question
2. Which of the following is not a unit of pressure?
a. mm Hg b. mbar c. torr d. Ncm
Answer: D, Ncm
Newton centimeter (Ncm) is a unit of torque. The other three units—millimeters of mercury (mm Hg), millibar (mbar), and torr—are all measures of pressure. (The two standard units of pressure missing from this list are pascal and atmosphere.)
Reference: General Chemistry 1 &2, Boise State University.
3. What evaporation flask shape is best for polymers and other viscous products?
a. evaporating cylinder b. powder flask c. foam brake d. spider
Answer: A, evaporating cylinder.
Viscous materials are more likely to stick to containers—such as an evaporation flask—and are difficult to transfer by pipette. You can make product recovery a little easier by using a cylindrical evaporation container, which has a lower surface area.
References: Aimee O’Driscoll, “Rotary Evaporator Accessory Options,” Rotovaps.net, March 2, 2021; Viscous Liquids Need Special Pipetting Techniques,” Eppendorf, April, 16, 2018
4. Which of the following has not been shown to improve solvent evaporation rate?
a. drink three cups of coffee instead of two b. increase rotation speed c. increase vacuum level and bath temperature d. increase evaporation flask size
Image Credit: Wikipedia
Answer: A, three cups of coffee.
Increasing rotation speed can make evaporation faster by increasing the surface area of the solvent; a larger evaporating flask works the same way. Increasing vacuum level and bath temperature can move the solvent nearer to its boiling point (although both should be done in moderation to prevent bumping and glassware implosion). Coffee has not been shown to speed up evaporation, but applying it to a chemist may speed other steps in a synthesis.
Reference: Aimee O’Driscoll, “How to Speed Up Your Rotary Evaporation Process,” Rotovaps.net, June 26, 2019.
5. What is the best way to prevent bumping or foaming, which can cause loss of product?
a. increase bath temperature b. use coated glassware c. use a system with a vapor sensor d. use only high-boiling solvents
Answer: C, use a vapor sensor
Bumping occurs when liquids superheat instead of boiling gently, so increasing the bath temperature raises the risk of bumping. And while using high-boiling solvents for every synthesis would be nice, it’s not always practical. Rotary evaporation systems with built-in foam and vapor sensors can adjust the system pressure automatically to dial back the risk of bumps.
Reference: “Heidolph—Getting the Most Out of Your Evaporator,” accessed Oct. 25, 2021.
6. Which of the following pairs of chemists worked out the math to describe a discontinuous phase transition?
a. Gibbs and Duhem b. Roche and Magnus c. Boyle and Dalton d. Clausius and Clapeyron
Answer: D, Clausius and Clapeyron.
The Clausius-Clapeyron relation describes how vapor pressure (or boiling point) changes with changing pressure, taking the enthalpy of vaporization into account. In other words, whenever you Google “[solvent] boiling point at [pressure],” you have Clausius and Clapeyron to thank for the answer you get.
Reference: “The Clausius-Clapeyron Equation."
7. Where in a rotary evaporator is the vapor tube located?
a. in the water bath b. inside the motor drive c. in the condenser d. mounted on the back
Answer: B, inside the motor drive.
The vapor tube is the piece of glassware that connects the evaporation flask to the condenser apparatus, passing through the motor drive.
References: "Rotary Evaporator Parts and Their Functions"; "Intelligent Evaporation," Heidolph
8. Which is the best type of pump to use with an evaporator?
a. peristaltic pump b. oil pump c. diaphragm pump d. rotary vane pump
Answer: C, diaphragm pump.
While both rotary vane and diaphragm pumps can be used to apply a vacuum in a rotary evaporator system, the user is likely to encounter more difficulties with a rotary vane pump. These pumps are best operated at complete vacuum, which is rarely required for efficient rotary evaporation, and running them at higher pressure can cause damage and accelerate maintenance schedules.
References: Rotovaps.
9. Which of these solvents has the highest boiling point?
a. water at atmospheric pressure b. dimethylformamide (DMF) at 75 mbar c. dichloromethane (DCM) at atmospheric pressure d. toluene at 200 mbar
Answer: A, water at atmospheric pressure.
At atmospheric pressure of about 1013 mbar, water boils at 100 °C and DCM at 40.7 °C. Toluene and DMF both have higher boiling points than water at atmospheric pressure, but under the vacuums specified both will boil at less than 100 °C.
Reference: “Solvent Data,” Heidolph Instruments.
10. Which of the following is the correct abbreviation of “rotary evaporator”?
a. rotovap b. rotavap c. Hei-VAP d. all the above
Answer: D, all of the above.
Whether you say rotovap, rotavap, or Hei-VAP, your labmates will understand what you mean! To learn more about the whole line of Hei-VAPs, check out heidolph-instruments.com
Reference: Heidolph Instruments.
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