Experiment - Recrystallization of a solid

Purpose

in this experiment acetanilide will be recrystallized from water, which serves as the solvent..


Pre-Lab Questions....

Explain the purpose of the following in this experiment.

a) using hot filtration

b) not cooling (chilling) the hot filtered solution immediately

c) washing the crystals in the final step with ice cold water

d) using gravity filtratoin ( not vacuum filration) in the hot filtration step

e) using a stemless funnel in the hot filration step

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in the experiment we have to determine the MP ( literature value 114 C ) ... and percent mass recovery of acetanilide in the orginal mixture ..

ANY clue how to approach to dese problems.. or is dere any kind of formula .. ot steps ..

THANKS A LOT

IS THERE ANYONE WHO CAN HELP ME >.>

Sarah--

I answered this for someone last night. Judging from the writing, I think I answered it for you. I have tried to find the original, which I think was posted under SCIENCE but I can't find it. Is there some specific question you have about any of my answers?

actually i copied the same question from there.. thts why u pretend that i am the same girl .. anywyz i couldn't get the answers from there .. thts i y .. i am asking u ... plz can u explain in detali if possible .. thnks do reply if u need any information ..

love u

If you can't get the answer from there it must mean that you don't understand all or portions of what I wrote for the answer. Thus it will do little good for me to simply repeat what I wrote (which I had started to do but stopped). Therefore, please explain what you don't understand and I shall try to rephrase my reply.

a) Using hot filtration: The purpose of using hot filtration in this experiment is to remove any insoluble impurities or solid contaminants that may be present in the solution. During recrystallization, the solid is dissolved in a hot solvent, and as the solution cools down, the solid recrystallizes. However, if there are any impurities, they may also crystallize out with the desired compound. By hot filtration, the hot solution is filtered to remove these impurities before cooling and recrystallization.

To perform a hot filtration, follow these steps:
1. Set up a filtration apparatus with a funnel and filter paper.
2. Heat the solution until it is near its boiling point.
3. While the solution is hot, quickly pour it into the funnel to filter out the insoluble impurities.
4. Collect the filtrate (filtered liquid) in a flask, which can then be cooled for recrystallization.

b) Not cooling (chilling) the hot filtered solution immediately: The purpose of not cooling the hot filtered solution immediately is to allow the desired compound to form larger, purer crystals. If the solution is rapidly cooled, the crystals that form may be small and impure, making it more difficult to obtain a good yield of the desired compound.

To prevent rapid cooling of the hot filtered solution, you should:
1. Allow the hot filtered solution to cool slowly at room temperature or in an ice bath.
2. The slow cooling process gives the molecules of the desired compound more time to arrange into well-defined and larger crystals.

c) Washing the crystals in the final step with ice-cold water: The purpose of washing the crystals with ice-cold water is to remove any remaining impurities that are adhered to the surface of the crystals. This step helps increase the purity of the obtained crystals.

To wash the crystals with ice-cold water:
1. Prepare a container of ice-cold water.
2. Transfer the crystals into a filter paper or Buchner funnel.
3. Slowly pour the ice-cold water over the crystals, ensuring thorough washing.
4. Collect the washed crystals, usually by air drying or using a desiccator.

d) Using gravity filtration (not vacuum filtration) in the hot filtration step: The purpose of using gravity filtration in the hot filtration step is to prevent the rapid cooling of the hot solution while filtering it. Using a vacuum filtration setup can cause the solution to cool too quickly, leading to the formation of small and impure crystals.

To perform gravity filtration in the hot filtration step:
1. Set up the filtration apparatus with a gravity funnel and filter paper.
2. Heat the solution until it is near its boiling point.
3. While the solution is hot, pour it into the funnel for filtration.
4. Allow the hot solution to pass through the filter paper under gravity.
5. Collect the filtrate for further processing, such as cooling and recrystallization.

e) Using a stemless funnel in the hot filtration step: The purpose of using a stemless funnel in the hot filtration step is to prevent any potential breakage due to temperature differences between the hot solution and the glassware. Stemless funnels are typically made of high-temperature-resistant materials like borosilicate glass, which can withstand the thermal stress during hot filtration.

To use a stemless funnel in the hot filtration step:
1. Choose a stemless funnel made of a suitable material.
2. Follow the steps for hot filtration mentioned earlier, using the stemless funnel for filtration.

For determining the melting point (MP) and calculating the percent mass recovery of acetanilide in the original mixture, you will need the following steps:

Determining the Melting Point (MP):
1. Obtain a pure sample of recrystallized acetanilide.
2. Set up a melting point apparatus according to the manufacturer's instructions.
3. Place a small amount of the recrystallized acetanilide in a capillary tube.
4. Insert the capillary tube into the melting point apparatus and heat gradually.
5. Observe the temperature range over which the acetanilide melts. The melting point should be close to the literature value of 114°C.

Calculating Percent Mass Recovery:
1. Determine the mass of the recrystallized acetanilide obtained after the recrystallization process.
2. Calculate the difference in mass between the original mixture (before recrystallization) and the recrystallized acetanilide.
3. Divide the difference in mass by the mass of the original mixture and multiply by 100 to obtain the percent mass recovery.

Remember, it is always important to consult the specific experimental procedures provided by your instructor or lab manual for accurate and detailed instructions in performing the experiment.