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Title; To purify benzoic acid crystals by recrystallisation .

Title; To purify benzoic acid crystals by recrystallisation . . Step 3 Crystals allowed to reform Recrystallisation. Step 1 Dissolve the impure Crystals Just enough hot water to do the job. Step 2 Hot filtration with suction Takes out non-soluble impurities. Step 4

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Title; To purify benzoic acid crystals by recrystallisation .

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  1. Title; To purify benzoic acid crystals by recrystallisation.

  2. Step 3 Crystals allowed to reform Recrystallisation Step 1 Dissolve the impure Crystals Just enough hot water to do the job Step 2 Hot filtration with suction Takes out non-soluble impurities Step 4 Cold filtration under gravity Takes out soluble impurities Step 5 Dry the pure crystals

  3. Step 1 – Dissolving the impure crystals The crystals are hardly soluble in cold water but very soluble in hot water (This is important for this procedure to work). Use just enough hot water to just dissolve the crystals, otherwise they may not come back out of solution later.

  4. Step 2 -Hot filtration with suction Three important points about this step • This step takes out all insoluble (visible) impurities. • It must be quick (hence the suction) to prevent crystals reforming at this stage. • It must be hot to prevent reforming of crystals on the funnel.

  5. Step 3 -Recrystallisation Two important points about this step • This crystals allowed to reform as the solvent cools down (recrystallisation). • The soluble impurities remain in the water and can now be filtered easily.

  6. Step 4 - Cold filtration under gravity In this step the pure crystals will be left on the filter paper and the remaining impurities will go through the filter paper with the water. In this step the melting point of the crystals is determined. If the crystals melt at exactly 123C they are pure. Step 5 – Allow to dry on filter paper Step 6 – Melting point determination

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