Lab 04 N
Filtration and Evaporation I
Separating the Components of a Heterogeneous Mixture
Pre-Lab Discussion:
Using the Introduction reading below, define each of the bolded terms in your own words (there
are 10). You should be able to get the bulk of the information you need below, but you may
augment your definition with information from other resources as you see fit.
Introduction:
If we mix sand and salt together, is the mixture a homogeneous mixture or a heterogeneous
mixture? It is heterogeneous because the mixture is not uniform in composition, not evenly
distributed and the components can be separated by physical means. A homogeneous mixture is
uniform in composition and components are evenly distributed.
Since the components can be separated, how would you, the student, go about separating the sand
from the salt? For example, what do you know about the ocean? Can you come up with some ideas
about separating sand from salt?
It is often necessary to separate a solid from a liquid. The most common process of separation
used in laboratories is filtration. During filtration, insoluble materials can be removed from a
liquid suspension. In a chemical reaction, we call the insoluble material a precipitate.
The solution is usually filtered through filter paper to catch the precipitate or insoluble material
that is suspended in the mixture or has settled to the bottom of the beaker. To avoid splashing
and to maintain control, the liquid may be poured down a stirring rod, but this is not always
necessary. Use the wash bottle to rinse out any solid left in the beaker. The solid trapped by the
filter paper should be rinsed with distilled water to remove any solvent particles. The rinse water
should also pass through the filter.
The liquid that passes through the filter paper is called the filtrate. The filtrate is often, but not
always, discarded. The solid trapped by the filter paper (precipitate or insoluble material) is
normally allowed to dry so that its mass can be determined. YOU WILL BE MARKED ON YOUR
ACCURACY OF THE AMOUNT OF SOLID COLLECTED. USE CARE AND GOOD TECHNIQUE!
Evaporation is a method used to separate components of a solution. Materials dissolved in a
solvent (water) can be separated by applying heat that drives off the solvent as a vapor, leaving
the solute (dissolved residue) behind. An evaporating dish containing the solution is placed on a
wire gauze and heated gently and evenly to avoid spattering the liquid.
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Purpose:
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to use filtration to separate an insoluble substance from a heterogeneous mixture
to use evaporation (differences in boiling points) to separate a soluble substance from a
solution (a type of homogeneous mixture)
Equipment / Materials:
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25 mL graduated cylinder
2 beakers, 100 mL / 150mL
funnel
ring stand with ring
evaporating dish
crucible tongs
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Sand
MSDS: 0, 0, 0
clay triangle
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wire gauze
wash bottle
Salt (NaCl)
MSDS: LOOK IT UP
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Electronic microbalance, reading to
0.001 g
Bunsen burner
stirring rod
filter paper
Procedure:
1.
Use a micro-balance and weigh boat to measure approximately 5 grams each of sand and salt.
Record the exact starting mass of each (to 0.001g) in your data table.
2. Mix your sand and salt with about 25 mL of tap water (use a graduated cylinder to measure
the water) in a small beaker.
3. Obtain a piece of filter paper, use a pencil to label it with your name or initials, and measure
its mass using a micro-balance. Record the mass of the paper (to a precision of 0.001 g) in
your data table. Fold the filter paper as shown in diagram above.
4. Pull one layer of the folded paper away from the rest forming a cone. Place the filter paper
cone in a funnel and wet it with distilled water. Press the paper carefully with your thumbs
so that it fits snugly in the funnel. Put the funnel into a small iron ring attached to a ring
stand. (If you can't find a small enough ring to hold your funnel, you can put the funnel into a
clay triangle that can then be placed on a larger ring.) Note that the tip of the funnel should
touch the upper inside wall of a small beaker below the funnel to prevent splashing.
5. Pour the mixture from the beaker into the filter paper cone. If the entire solid does not
come out of the beaker, rinse the beaker with small amounts (not more than a total of 5-6
mL) of distilled water from your wash bottle, and then pour this extra water and the
remainder of the solid into the filter paper cone. You may need to loosen the solid from the
bottom and sides of the beaker with a stirring rod. DO NOT discard the filtrate.
6. Rinse the solid in the filter paper with distilled water to remove any excess solvent.
7. Then, when filtering is complete, carefully set the cone of filter paper on a FOLDED paper
towel to absorb some of the excess water on the filter paper. Put your filter paper and solid
onto the class tray at the front of the room to dry overnight.
8. Carefully pour the filtrate into the evaporating dish and set it on the wire gauze over a low
flame as shown in the diagram above. Cover the evaporating dish with a watch glass and
gently heat the filtrate until you observe a change (note this in your data table). Some
popping and spattering may occur during evaporation, but an excessive amount indicates that
you’re heating too rapidly. Record your qualitative observations of the dissolved substance in
the filtrate solution before and after evaporation.
9. Allow the filter paper and the solid to dry overnight. After that time, determine the mass
of the filter paper and solid (to a precision of 0.001g). Record all of your data in your Data
Table.
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Data and Observations:
Make a table to record your qualitative observations (include a title for your table):
Observations of the sand
Observations of the salt
Observations of the sand and salt mixture
Observations of dissolved solute from filtrate before and after evaporation
Observations of … record all other qualitative observations in an organized fashion
Make a second table to record your quantitative data. Include a title and column headings for your
table. Don’t forget to put the units and the uncertainty of your measurements in the column
heading:
Exact starting mass of sand
Exact starting mass of salt
Mass of Filter Paper
Mass Paper + insoluble solid
Mass of insoluble solid
…g
…g
…g
…g
…g
Clean Up:
Wash all glassware and return each piece of equipment to its proper location. Pour excess filtrate
in the appropriate waste beaker. Also put your filter paper with the dried solid in the waste
beaker provided after it has dried and you have measured its mass. (the next day)
Data Analysis:
Based on your exact starting mass of sand in the experiment, calculate the percent error for the
sand you collected on your filter paper. Show every step of your work, including the original
equation (without numbers) and the substitution into the equation. (hint: which if your
measurements is the theoretical amount of sand you expected to get in your filter paper?)
Summary:
(answer in paragraph form) What do you think the composition of your filtrate was? Do you have
evidence that it was pure water? Do you have evidence that it contained a dissolved solute? If so,
what do you think it was? What was the evidence? Discuss what you would have expected to see if
you had evaporated all of the water out of the evaporating dish.
In paragraph form, discuss your experimental results (how much error did you have according to
your percent error?) and evaluate your technique (in other words, how could you improve your
technique?) Also discuss errors due to the procedure (error that can not be attributed to
instrument error or human error).
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