Low recovery

The question is: A student performs a crystallization on an impure sample of biphenyl. The sample weighs 0.5g and contains about 5% impurity. Using his knowledge of solubility, he decides to use benzene as a solvent. The final weight is only 0.02g. Why is recovery so low?

My answer: The recovery is low because there will be some experimental loss, the original sample was not 100% biphenyl, and some biphenyl is soluble in the solvent even at 0 degrees C.

Is this sufficient?

Thanks from Sheryl


I would hit it little harder in spots. With a known impurity of 5%, we might expect to recover about 0.45 g. Some additional loss could be expected due to solubility in the solvent regardless of the solvent used. However, a recovery of only 0.02 g far exceeds looses due to solubility if the proper solvent was used for recrystallization and in the right amount. The loss in this case is due to the high solubility in benzene. Perhaps too much solvent was used. (The Merck Index says biphenyl is insoluble in water--which we would expect--and soluble in alcohol and ether. It doesn't mention solubility in benzene' however, solubility in ether suggests solubility in benzene,too My guess, then is that the student simply used too much benzene and his/her problem is loss in the solvent.)

  1. 👍 0
  2. 👎 0
  3. 👁 2,328
  1. Ha I'm doing the same problem right now. I'm pretty sure its because the biphenyl will dissolve completely in the benzene at room temperature (not good for crystallizations).

    1. 👍 0
    2. 👎 0
  2. Thank you so much. I'm struggling for this question from last night.

    1. 👍 0
    2. 👎 0

Respond to this Question

First Name

Your Response

Similar Questions

  1. Chemistry

    A student is given a sample in lab which contains one of the ions listed below. After adding a few drops ofsolution to part of the unknown sample, the student got a greyish precipitate. After adding a few drops ofsolution to

  2. chemistry

    treatment of a 0.400g sample of impure potassium chloride with an excess of AgNO3 resulted in the formation of 0.733g of AgCl. calculate the percentage of KCl in the sample. show balanced equations in support of your answer

  3. chemistry

    A 0.1028 g impure sample consists of Na2CO3 was analyzed by the Volhard method. After adding 50.00 mL of 0.06208 M AgNO3, the sample was back titrated with 0.06261 M KSCN, requiring 28.36 mL to reach the end point. Report the

  4. Sample purity

    Question: A student spots an unknown sample on a TLC plate and develops it in pentane solvent. Only one spot, for which the Rf value is 0.05, is observed. Is the unknown a pure compound? What can be done to verify the purity of

  1. Chemistry URGENT

    A student heated a hydrated salt sample with an initial mass of 4.8702 g, After the first heating, the mass had decreased to 3.0662 g (two part question) 1. if the sample was heated to constant weight after reheating, what is the

  2. chemistry

    Hi, I need help figuring out this question. An impure sample of barium hydroxide, Ba(OH)2 (aq), has a mass of 0.540 g. It is dissolved in water and then treated with excess sulfuric acid, H2SO4(aq). This results in the formation

  3. chemistry

    determine the % of water of crystallization in pure sample of green vitriol (FeSo4.7H2O)

  4. College-Chemistry

    NaOH(s)+ H2SO4(aq)=Na2SO4(aq) + H2O(l) Consider the unbalanced equation above.A 0.900 g sample of impure NaOH was dissolved in water and required 37.0 mL of 0.145 M H2SO4 solution to react with the NaOH in the sample. What was the

  1. Rf values

    Question: Consider a sample that is a mixture composed of biphenyl, benzoic acid and benzyl alcohol. The sample is spotted on a TLC plate and developed in a dichloromethane-cyclobutane solvent mixture. Predict the relative Rf

  2. Naphthalene

    Question: You are about to purify an impure sample of naphthalene by column chromatography. What solvent should you use to elute the sample? My answer: Naphthalene is very nonpolar so a very nonpolar solvent like hexane should be

  3. science

    A scientist performs tests on a sample of an element. The element is a shiny solid that conducts electricity and heat. The scientist is able to bend and flatten the sample when pressure is applied to it. Based on this information,

  4. Government

    1) The portion of the population selected to participate in a poll is known as the a. public b. population c. deliberative group d. sample e. focus group 2) A sample that does not overrepresent any portion of the population and

You can view more similar questions or ask a new question.