CHEM 162 EXPERIMENT #5
SPECTROCHEMICAL SERIES EXAM SCRIPT
2026 TEST PAPER QUESTIONS AND
SOLUTIONS GRADED A+
◉ What is the specialized melting point technique that is used to
determine the identity of an unknown compound? Answer:
Comparative Melting Point --
this is when you make a 50:50 mixture of the unknown compound
and the substance you think it is based off given melting point values
◉ What are the five steps of re-crystallization? Answer: 1. Choose an
appropriate solvent
2. Dissolve the impure mixture in the solvent
3. Remove the insoluble impurities via filtration
4. Crystallize the pure compound from the solution
5. Isolate the pure compound via suction filtration
◉ List two different methods for inducing precipitation in a solution
that fails to produce crystals after cooling in an ice bath Answer: 1.
Scratching the wall of the flask with a stirring rod
2. Introduce a seed crystal that matches the pure compound
,◉ What specific technique is used to collect/isolate the insoluble
impurities from your solution? Answer: Gravity Filtration
◉ List the four characteristics of a good recrystallizing solvent?
Answer: 1. Must be fully solvable at high temperature, but NOT at
room temperature
2. Impurities must be soluble at room temperature OR insoluble at
high temperature
3. Solvent must be chemically inert
4. Solvent must be suitably volatile in nature
◉ How does the presence of impurities effect the melting point of a
solid, crystalline substance? Answer: Broadens and depresses the
melting point range
◉ How do you calculate percent recovery? Answer: (mass of final
product / mass of starting product) x 100%
◉ Why would it be a bad idea to use an excessive amount of water to
dissolve your unknown when recrystallizing? Answer: It would
lower the amount of unknown actually recovered in the process; as
, well as increase the amount of time needed to complete the re-
crystallization process
◉ Why would it be a bad idea to use cold water to dissolve your
unknown when recrystallizing it? Answer: Re-crystallization could
happen too fast when using cold water
◉ Melting points are lowered by the presence of impurities. For this
experiment, what is the most likely impurity that will affect the
observed melting point of your unknown? Answer: Impurities may
be from the sand, but most likely the impurity was from the amount
of water that was used
◉ A student is presented with a heterogeneous mixture of two solids
(A & B). Using the table provided below, determine which of the
following solvents (X, Y, or Z) would be an appropriate choice for
isolating and recrystallizing Unknown A from Unknown B? Explain
the reasoning behind your decision in detail. Answer:
◉ After recrystallizing an unknown solid, you obtain a preliminary
melting point range of 134-139 Celsius. Identify your purified
unknown using the table below. Which of these compounds is your
unknown most likely to be? Answer:
◉ Compound H is soluble in ethanol at 78.4 Celsius (2.3 g/100 mL).
If you were given an 800 mg sample of Compound H, what specific
SPECTROCHEMICAL SERIES EXAM SCRIPT
2026 TEST PAPER QUESTIONS AND
SOLUTIONS GRADED A+
◉ What is the specialized melting point technique that is used to
determine the identity of an unknown compound? Answer:
Comparative Melting Point --
this is when you make a 50:50 mixture of the unknown compound
and the substance you think it is based off given melting point values
◉ What are the five steps of re-crystallization? Answer: 1. Choose an
appropriate solvent
2. Dissolve the impure mixture in the solvent
3. Remove the insoluble impurities via filtration
4. Crystallize the pure compound from the solution
5. Isolate the pure compound via suction filtration
◉ List two different methods for inducing precipitation in a solution
that fails to produce crystals after cooling in an ice bath Answer: 1.
Scratching the wall of the flask with a stirring rod
2. Introduce a seed crystal that matches the pure compound
,◉ What specific technique is used to collect/isolate the insoluble
impurities from your solution? Answer: Gravity Filtration
◉ List the four characteristics of a good recrystallizing solvent?
Answer: 1. Must be fully solvable at high temperature, but NOT at
room temperature
2. Impurities must be soluble at room temperature OR insoluble at
high temperature
3. Solvent must be chemically inert
4. Solvent must be suitably volatile in nature
◉ How does the presence of impurities effect the melting point of a
solid, crystalline substance? Answer: Broadens and depresses the
melting point range
◉ How do you calculate percent recovery? Answer: (mass of final
product / mass of starting product) x 100%
◉ Why would it be a bad idea to use an excessive amount of water to
dissolve your unknown when recrystallizing? Answer: It would
lower the amount of unknown actually recovered in the process; as
, well as increase the amount of time needed to complete the re-
crystallization process
◉ Why would it be a bad idea to use cold water to dissolve your
unknown when recrystallizing it? Answer: Re-crystallization could
happen too fast when using cold water
◉ Melting points are lowered by the presence of impurities. For this
experiment, what is the most likely impurity that will affect the
observed melting point of your unknown? Answer: Impurities may
be from the sand, but most likely the impurity was from the amount
of water that was used
◉ A student is presented with a heterogeneous mixture of two solids
(A & B). Using the table provided below, determine which of the
following solvents (X, Y, or Z) would be an appropriate choice for
isolating and recrystallizing Unknown A from Unknown B? Explain
the reasoning behind your decision in detail. Answer:
◉ After recrystallizing an unknown solid, you obtain a preliminary
melting point range of 134-139 Celsius. Identify your purified
unknown using the table below. Which of these compounds is your
unknown most likely to be? Answer:
◉ Compound H is soluble in ethanol at 78.4 Celsius (2.3 g/100 mL).
If you were given an 800 mg sample of Compound H, what specific
