Physical Methods Lab
Aka – Filtration Lab
Background Information
Some naturally occurring materials are mixtures of two or more substances. Heterogeneous
mixtures are obviously two or more substances because one can see different components.
Homogeneous mixtures have the appearance of being uniform throughout. One cannot see the
individual component particles. In either case, mixtures of compounds may be separated into
their component parts through a variety of different physical methods.
Physical methods of separation use differences in physical properties of the components of a
mixture, such as solubility, boiling point, density, or melting point. Here is an introduction to
some physical methods available to us:
1. Decantation is a process for separating the liquid component of a solid-liquid mixture
from the solid by pouring. The solid is allowed to settle to the bottom of the container.
The liquid is then carefully poured from the vessel containing the mixture without
disturbing the solid. This liquid is called the supernatant liquid.
2. Filtration is a process for separating a solid from a liquid by passing the liquid
through a porous material such as filter paper. The solid is unable to pass through the
pores in the filter paper and remains on the filter paper. This solid is called the
residue. The liquid that passes through the paper is called the filtrate. For example, we
can separate the components of a heterogeneous mixture of solid AgCl and water by
filtration. In such a separation, AgCl is the residue, and water is the filtrate.
3. Evaporation is a separation process in which a solution is heated to remove the
solvent. The substance, or residue, remaining after the solvent has evaporated is the
substance originally dissolved in the solvent. For example, we can separate the
components of a homogeneous mixture of potassium bromide (KBr) dissolved in
water by evaporation. When we heat the solution, the solvent, water, evaporates
which leaves the residue, KBr.
4. Extraction is a separation process that can be used when one component of a binary
mixture is soluble in an added solvent and the other is not. The component that is
insoluble in the extracting solvent can be recovered by filtration. For example, we can
separate the components of a heterogeneous mixture of solid KBr and solid AgCl by
extraction with water. When we place the mixture in water, KBr dissolves and AgCl
does not. We can then recover the AgCl by filtration. Finally, we can evaporate the
solvent from the filtrate to recover the KBr.
5. Chromatography is a process where different compounds are separated by differing
solubility in two phases, a stationary phase (usually a solid) and a mobile phase (a
liquid or a gas). Each compound begins their journey across the stationary phase at
the same point. As the mobile phase passes across the stationary phase, it picks up
each compound and moves it across the stationary phase. This movement is
dependent on the attractive forces holding each compound to the stationary and
mobile phases. A compound, which has a high affinity to the mobile phase, will move
faster and farther than a compound that has a high affinity for the stationary phase.
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Physical Methods Lab
Aka – Filtration Lab
The components of a mixture of sand (Si02) and sodium chloride (NaCl) can be
separated from one another using water as a solvent. You will separate the components by
adding water, filtering the insoluble SiO2, and evaporating the water from the filtrate to
recover the solid NaCl.
Procedure
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Obtain a vial containing NaCl and Sand in an undisclosed proportion. Record
your unknown number in your notebook.
Determine the mass of the entire sample by weighing the vial before and after
you empty it.
Measure out 50 mL of deionized water and add this to your mixture. Stir well for
a minimum of 2 minutes.
Filter this mixture through a funnel being careful not to lose any of the liquid or
solid.
Rinse the entire solid into filter paper making sure to remove any possible
sodium chloride.
Dry the sand in the oven.
Take the liquid collected from the filtration and heat it to boiling on a heating
mantel. Continue to boil this solution until only 10 ml remain.
Transfer this beaker to the oven to complete the drying process.
Determine the mass of each component.
Calculations
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Calculate the original mass of your unknown
Calculate the amount of sand you obtained.
Calculate the amount of sodium chloride you obtained.
Calculate the total amount of unknown recovered (2 + 3).
Calculate the percent NaCl in the sample (3/1 x 100).
Calculate the percent sand in the sample (2/1 x 100).
Calculate percent recovery of all components (4/1 x 100).
Discussion area possibilities
1. Discuss other uses for filtration.
2. If your sand or sodium chloride wasn't dry at the end of your experiment,
how would that affect your data?
3. Do you think each can be used?
4. What other techniques can you think of that can separate compounds?
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