I was asked to write up the experiment that we did in class, but i was absent that day, and i really don't know anything about it, could someone please help me,
the title of the experiment says : To obtain a pure sample of benzoic acid form an impure sample by the technique of recrystallisation.
that was part A
and the part B : To measure the melting point of benzoic acid
thank you for help
You can't really write up an experiment that you have not done.
It is usaully recrystallzed from water as it is very soluble in hot water and not very soluble in cold water. The result is needle shaped crystals.
I have no idea which method you will have used for the melting point. Simplest is a melting poitn apparatus. My school group used to use a boiling tube containing oil and the sample tied to a thermometer in the oil. The tube was heated by a bunsen.
Of course, I can help you with that. To write up the experiment, you will need to understand the procedure and the purpose of each part. Here's a step-by-step guide on how to write it:
Part A: To obtain a pure sample of benzoic acid from an impure sample by the technique of recrystallization.
1. Start by explaining the purpose of recrystallization, which is a common technique used to purify solids.
- Describe how impurities can be removed through the process of dissolving and recrystallizing.
2. Briefly explain the composition and impurities of the initial sample of benzoic acid.
- Note that the impure sample of benzoic acid contained various impurities that hinder its use.
3. Describe the steps of the recrystallization process you would normally follow in the lab:
a. Dissolving the impure sample:
- State that a suitable solvent (such as hot water) was chosen to dissolve the impure benzoic acid.
- Emphasize that the solvent must be selective, meaning it should dissolve the impure compound but not the desired one.
b. Filtering the solution:
- Explain that the solution was then filtered to remove insoluble impurities.
- Mention the use of a filter paper or a vacuum filtration apparatus for this purpose.
c. The recrystallization process:
- Explain that the filtrate was cooled slowly to allow the pure benzoic acid crystals to form.
- Highlight that slow cooling helps obtain larger and purer crystals.
d. Collecting and drying the crystals:
- State that the obtained crystals were collected by filtration or centrifugation.
- Note that the crystals were then washed with a cold solvent to remove any remaining impurities.
- Finally, highlight that the clean crystals were dried to obtain the pure sample of benzoic acid.
Part B: To measure the melting point of benzoic acid.
1. Explain the importance of measuring the melting point in the characterization of a substance.
- Emphasize that the melting point is a unique physical property that can be used to identify a compound.
2. Briefly describe the principle of melting point determination.
- Mention that the melting point is determined by heating the substance until it changes from a solid to a liquid state.
- Add that the melting point can be accurately measured using a melting point apparatus, which detects the melting point range.
3. Detail the procedure you would use to measure the melting point of benzoic acid:
a. Preparation of the sample:
- Explain that a small amount of the purified benzoic acid sample was placed in a capillary tube.
- Mention that the tube was carefully sealed and attached to the melting point apparatus.
b. Heating and observation:
- State that the temperature was gradually increased until the benzoic acid sample melted.
- Note that the melting process was observed carefully, recording the temperature at which the melting began and completed.
4. Discuss the expected melting point range and its significance for pure benzoic acid.
- Indicate that pure benzoic acid has a known melting point range of approximately 121-123°C.
- Mention that a melting point within this range suggests a high degree of purity.
Remember to format your write-up clearly, use appropriate scientific language, and include any calculations or observations necessary for a complete report.