PRE-LAB QUESTIONS - WEEK 1 Why would you add boiling chips/stones to a solution
ID: 714338 • Letter: P
Question
PRE-LAB QUESTIONS - WEEK 1 Why would you add boiling chips/stones to a solution that is to be refluxed? When should you add them? 1. 2. What is the definition of a reflux? What happens to the solvent during a reflux experiment? What are three characteristics of a "good" solvent to use for refluxing? You are asked to reflux a solution for one hour. At what point does the reflux time start? What is the temperature of the solution during the reflux? 3. Should you report a melting point as a single number or a range? How are the high and low endpoints of the range determined experimentally during the melting point experiment? What is the relationship between the purity of a compound and its melting point range? 4. 5. Briefly describe how a rotary evaporator works. What is likely to happen if cooling water is not run through the condenser when solvent is vaporized using a rotary evaporator? That is, where is the solvent likely to end up?Explanation / Answer
1. Boling stones are used for uniform boiling the solution. Boiling stone prevents bumping of reaction mixture. It has pores and vapours from that pore are contineously bubbling the solution. They should be added whenever there is long boiling/ reflux is going on.
2. Reflux is a technique in which the condensation of vapours and the return of the condensate to the system from which it is originated. Reflux is long term boiling of the solution using condensor. In reflux solvent from solution is get evaporated and gets condensed back into the water condensor. Thus boiling is made for long time and reaction molecule will get sufficient heat.
Good refluxing solvent should have high boiling point and it should not be volatile.
It should stand at high temperature and should be sufficiently stable.
3. Refluxing time starts when your solution starts the boiling. The temperature of solution during reflux is equal to its boiling point.
4. Melting point should be reported as a single temperature and not at a range.
Lower end of melting temperature is the temperature when substance starts melting and higher end is the temperature when substance is completely melt.
If the impurities are in the substance then it decreases the melting point of it.
Impure compound have lower MP.
5. In rotary evaporatore there is a motor which rotates the solution in evaporation flask. At its axis there is vapour duct. There is vacuum system which reduces pressure. Water bath is there to heat the solution. Coiling water condenser is present for condensation.
If condenser has cooling water it condenses solvent vapours and if it is absent then vapours will leave and solvent level will decrease.
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