Lesson 3 - Page 1



Discover the difference between solutions and mixtures.

Solids are readily separated from liquids by passing the mixture through a filter, a barrier with many small openings.  This method is called filtration.  This is a simple method for separating sediment from water in the course of the treatment of water for drinking purposes, because the particles of sand and clay making up the sediment do not pass through the filter.

Chemists keep containers of pure chemicals called reagents on their shelves.  Reagents are used in many lab test to identify unknown substances or to conduct experiments.  Since reagents are known substances, they can help discover unknown substances. 

The iron sulfate that is in the solution passes through the filter paper for the simple reason that the smallest units of iron sulfate and the smallest units of water are much smaller than the holes of the filter paper.  The particles of white material are too large to pass through the filter paper.  Chemists use filters with different sized holes. 

The original mixture - the tablets dissolved in warm water, that you filtered is called a suspension because some of the material, the neutral component was suspended in water.  When you shake a suspension, it looks cloudy.  True suspensions eventually settle if you allow them to stand long enough, and you can then separate the components by pouring off the solution that remains on top.  The residue remains on the bottom.  Filtering is a faster way of separating a filtrate from its residue. 

Put the tablets in the measuring cup.  Cover with about 1/2 cup of water.  Stir.  Notice that the dark outer coating of the tablet comes off and stains the water.  Soak the tablets until the coating is completely dissolved.  Rise the tablets under the faucet.  They should be white.  Rinse out the cup, fill it with about 3/4 cup of warm water, and put the tablets in the cup.  Stir until the tablets break up.  The white powdery material that does not dissolve is a neutral material used by pharmaceutical firms in the manufacturing of the tablets.

To collect your iron sulfate solution and separate it from the white powder, filter the mixture.  Open the coffee filter.  Set the funnel in the jar.  Stir the mixture well, then pour it into the filter.  The material that passes through the filter is called the filtrate.  The material trapped by the filter is called the residue.  Let the filtrate drain into the jar.  Cover the jar and label it.


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