EXPERIMENT 2: SEPARATION OF THE COMPONENTS OF A MIXTURE
In this lab, we will be taking a mixture of three substances and separating them based on some of their
physical properties. The mixture you will be working with is composed of ammonium chloride (NH 4Cl),
sodium chloride (NaCl) (table salt) and silicon dioxide (SiO2) (sand).
MATERIALS
Mixture to separate and analyze
Balance
spatula
Tongs
Bunsen Burner
2 Evaporating dish or crucible
Ring stand and ring
1 Watch glass
Clay triangle
Glass stick or stir rod
25 mL graduated cylinder
PROCEDURES:
PART 1:
1.
2.
3.
4.
5.
6.
7.
8.
Obtain a clean, dry evaporating dish and record the mass, i.e. evaporating dish #1.
Add about 2 grams of your assigned mixture into evaporating dish #1. Record the new mass.
Determine the mass of the mixture added.
Setup the heating apparatus, the Bunsen burner, tripod
and wire gauze.
Heat the mixture on high heat for at least 20 minutes. Use
a glass stick to agitate the mixture. White “smoke” will start
to evolve when the sample becomes hot. This is the
ammonium chloride subliming in the evaporating dish. Do
not touch the dish with your hands. Hot things look just like
cold ones!
Let the evaporating dish cool and its contents cool.
Reweigh the dish and its contents. Record the mass. (Do
not weigh a hot or warm dish, convection currents can
affect mass reading by balance.)
Determine the mass lost to sublimation (i.e. mass of ammonium chloride)
PART 2:
9. a) Add 25 ml of water to the remaining salt/sand mixture and b) stir for approximately five minutes.
10. Let the residue settle for approximately 3-5 min.
11. Tare a clean evaporating dish covered with a watch glass, i.e. evaporating dish #2.
12. Remove the watch glass and decant the extract from the salt/sand mixture into the evaporating dish # 2,
making sure not to transfer any solid residue. It is better to leave a small amount of solution in the sand than
to get the sand in the evaporating dish # 2.
13. Add 10mL more of water to the residue in the evaporating dish # 1, stir and
decant as described in steps 9b), 10 and 12
14. Repeat with another 10mL of water.
15. Place the evaporating dish # 2 on the wire gauze supported on a tripod above
a Bunsen burner.
16. Gently evaporate the water from the salt water extract until most of the water
is gone.
17. Near the end, cover the evaporating dish with the watch glass to prevent splattering.
18. When the salt is completely dry, no more water will condense on the watch glass. Carefully remove from the
Bunsen burner and allow to cool. Go to step 20. While you wait for cooling to occur.
19. Weigh the evaporating dish with the dried salt and watch glass. Record its mass and use it to calculate the
mass of the salt.
PART 3:
20. Place the evaporating dish # 1 with the sand on the wire gauze and heat for approximately ten minutes over
a low fire. Do not overheat or the dish may break.
21. Carefully remove from the Bunsen burner and allow to cool. Go to step 19 if the dish is cool.
22. Weigh the evaporating dish with the dried sand. Record its mass and use it to calculate the mass of the
sand.
23. Determine the percent composition for each chemical and the overall recovery of the mixture. Provide the
answer on the datasheet below. Show your answer to your lecturer before you leave the lab.
Percent composition =
mass of component ×100%
Mass of initial mixture
The procedures for the lab are summarized by the flow chart below:
Mixture of NaCl, SiO2
and NH 4Cl
Heated
Sublimed NH4Cl
( obtain mass by
difference)
Remaining after heating
Mixture of NaCl and
SiO2
Extract with
(dissolved
Solution of NaCl
Heat to
dryness
NaCl (s)
Obtain mass
water
NaCl)
insoluble in water
(residue)
Wet SiO2
heat to
SiO2(s)
Obtain mass
dryness
Analysis Questions:
1. What physical properties were used to separate the different components of the mixture? In your results/data
section compare these properties for ammonium chloride, sand and salt in the form of a table. In this table
include physical state at room temperature as a property. Comment on it in your discussion.
2. Elaborate on the different separating techniques used in this lab, relating it to the actual experiment
conducted and the physical properties listed in #1 above. Hint: There are at least four different separating
techniques used in this experiment.
3. Add up the masses of your individual ingredients. Do they match the mass of your original mixture? Did you
get a 100% recovery? Discuss reasons why this might happen. Note- acceptable reasons for errors in lab
are not “human error” or “calculation error”. Be specific (refer to a step(s) in the lab and discuss what might
have happened).
4. How does this lab illustrate the law of conservation of mass?
5. Naphthalene sublimes while potassium chloride does not. Potassium chloride is soluble in water. How might
you separate a mixture of iron filings, naphthalane and potassium chloride? Show with a flow chart similar
to the one used to describe the procedure in this lab.
6. A student obtains the following final results: NaCl = 51%, NH4Cl = 32%, SiO2 = 34%
Think about the law of conservation of mass (matter) and describe the discrepancy that exists. What could
have caused it in this lab?
EXPERIMENT 2: SEPARATION OF A MIXTURE Name: _____________________________
RESULTS:
Partners name: ____________________________
a) mass of evaporating dish #1
b) mass of evaporating dish #1 + mixture
__________________ g
__________________ g
c) mass of mixture
__________________ g
What chemicals are present in the mixture?
d) mass of evaporating dish #1 + mixture after heating
__________________ g
e) mass of ammonium chloride (NH4Cl)
__________________ g
What chemicals are left in the mixture now?
f) % of ammonium chloride in original sample
Show __________________ %
working here for f):
g) mass of evaporating dish #2 + watchglass
__________________ g
h) mass of evaporating dish #2 + watchglass+ NaCl
__________________ g
i) mass of sodium chloride (NaCl)
__________________ g
j) % of sodium chloride in original sample
Show __________________ %
working here for j):
k) mass of evaporating dish #1 + SiO2
__________________ g
l) mass of silicon dioxide (SiO2)
__________________ g
m) % of silicon dioxide in original sample
Show __________________ %
working here for m):
n) sum of masses of NH4Cl, NaCl and SiO2 (e+i+l)
__________________ g
o) % recovery [(n/c)x100%]
__________________ %
EXPERIMENT 2: SEPARATION OF A MIXTURE
Name: _Alexa Acosta________ Pre-Lab
Define the following terms and give an example in each case.
Mixture – when two or more substances are combined, but they are not combined
Example: seawater
Substance – a particular kind of matter with uniform properties
Example: salt
Compound – something made up of two or more separate elements
Example: water
Element – is a chemical substance that cannot be broken down into other substances
Example: gold
Solution- is a homogeneous mixture of one or more solutes dissolved in a solvent
Example: rubbing alcohol
Extraction - the process of selectively removing a compound of interest from a mixture using solvent.
Example: making tea
Sublimation (besides NH4Cl) – the transition of a substance directly from a solid state to a gas state
Example: dry ice
Taring: a deduction from the gross weight of substance and its container made in allowance for the
weight of the container.
Examples: the weight of the container
Physical change- occurs when objects or substances undergo a change that does not change their
chemical composition.
Example: freezing
Chemical change – this occurs when a substance combines with another to form a new substance
Example: milk going sour
Physical property: a characteristic of matter that may be observed and measured without changing the
chemical identity of a sample
Example: boiling point
Label the processes of physical separation illustrated in the diagrams below based on the
descriptions given on the following page .
Chromatography
Filtration
Centrifugation