Separation of Mixtures

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Separation of Mixtures
Intro to Chemistry Chem1020 Lab

• Chemistry Department
• Minneapolis Community Technical College

2
Overview

• Part I
• Schematic demonstration of the overall procedure
• Part II
• Mass measurement
• Part III
• Physical method sublimation
• Part IV
• Physical method filtration
• Part V
• Calculation

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Part I. Procedure

• In this experiment, you will be given a solid
  mixture that contains three substances. They are
  ammonium chloride, sodium chloride, and sand.
  Your goal is to separate the mixture into these
  three substances, then determine the mass and
  composition percentage of each substance. Two
  physical methods, sublimation and filtration,
  will be used to separate the components.

Make sure to record this unknown number on your
data sheet.
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8. Weigh the paper and the sand after drying
(Mpapersand).
1. Weigh the empty evaporating dish (Mdish)
7. Add water which dissolves sodium chloride
only. Filter out the sodium chloride and water
with filter paper. Only sand will be left on the
paper.
2. Add solid mixture
4. Heat the dish. Ammonium chloride sublimes into
gas and escapes.
6. Weigh a piece of filter paper (Mpaper).
5. Weigh the dish with just sodium chloride and
sand left (Mdishmixture after heating)
3. Weigh the dish with the mixture (Mdishmixture)
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Part II. Mass Measurement

1. Always use the same balance during one experiment
   and record the balance number.
2. Always have a piece of weighing paper on the
   balance.
3. Before putting your object on the balance, press
   the Zero or Tare button to zero it.

weighing paper
balance number
zero button
A top-loading balance

1. Carefully put the object on the balance, and
   record all digits shown in the display (including
   zeros) with the unit of g. Example this
   evaporating dish is 36.66 g.
2. Avoid spilling. If it ever happens, alert the
   instructor.
3. Never put a hot object on the balance!

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Part III. Sublimation

• Since the gaseous ammonium chloride is hazardous
  when inhaled, perform this procedure in the fume
  hood!!!

• Heat the mixture in the dish with a Bunsen
  burner. Review the next slide for how to light
  up the burner.
• Stop heating when there is no more white fume
  forming (what substance is it?) and no yellow
  color left in the solid mixture.
• Carry the hot evaporating dish back to your
  station with a beaker.

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How to Light up a Bunsen Burner? An Important
Skill in a Chem Lab
1. Connect the burner and the gas valve with a
rubber hose.
2. Gently close the gas valve of the burner.
3. Gently close the air valve of the burner.

• Approach a lit stick or a striker to the top of
  the barrel.
• Meanwhile quickly turn on the gas valve of the
  burner.

Hottest spot

1. Turn on the air valve until you see two blue
   cones formed in the flame.

4. Turn to open the gas valve.
A striker
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Part IV. Filtration
Folding the filter paper
John D.
Funnel
Clay triangle
1. Weigh and label
1. Open the paper cone with 3 layers on one side
and one layer on the other side.
John D.
2. Fold into halves with name facing inside
Filtration apparatus
2. Wet the paper with water.
3. Fold into halves again
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3. Pour the sand, sodium chloride, water mixture
into the filter paper cone. Rinse the
evaporating dish with distilled water to transfer
all of the solid.
4. Wash the solid remaining on the paper with
more water to remove residual sodium chloride.
John D.
John D.
5. What is remaining on the paper now? Remove
the paper and open it up onto a watch glass. Dry
in the oven.
6. Weigh the dried sand with the filter paper.
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Part V. Sample Calculation

• Data
• Mevaporating dish 36.66 g
• Mdishmixture 39.06 g
• Mdishmixture (after heating) 38.05 g
• Mfilter paper 0.82 g
• Mpapersand 1.24 g

For some reasons that will be explained later in
the semester, when you do subtraction in this
calculation, always keep two decimal places.
However it is more complicated with dividing. To
make it simpler, always keep one decimal place in
this calculation.
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Calculation Mmixture Mdishmixture -
Mevaporating dish 39.06 g 36.66 g
2.40 g Mammonium chloride Mdishmixture -
Mdishmixture (after heating) 39.06
g 38.05 g 1.01 g Msand Mpapersand -
Mpaper 1.24 g 0.82 g 0.42 g Msodium
chloride Mmixture - Mammonium chloride -
Msand 2.40 g 1.01 g 0.42 g 0.97
g
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• Wash all used glassware clean with tap water and
  put them back to the bench.
• Dispose of the used sand into the designated
  waste container.
• Dispose of the used filter paper into trash.
• Wipe your bench and fume hood with wet sponge.
• Ask your instructor to sign you out.then you are
  ready to leave.
• Finish the lab report (including both data sheet
  and postlab questions) after the lab. Feel free
  to ask instructors questions, but never ever copy
  other students answers.
• Turn in the lab report the next time when you are
  expected to come to the lab.
• Dont forget to prepare for the next lab before
  you come next time.