Vacuum Filtration

Filtration is a technique that enables us to separate solids from liquids in the

laboratory. The solids become trapped because they are too large to pass

through the piece of filter paper, while the liquid

travels through the paper.

Vacuum filtration uses the same idea while also

pulling a vacuum inside the filter flask to increase the

flow rate of liquid through the filter paper.

After filtration is completed, all the solid is stuck to

the filter paper. It is difficult if not impossible to

separate completely the filter paper from the solid at

this point.

If you are trying to quantify the mass of the solid,

which type of mass measurement technique should

you use? Massing by difference is needed when using

filter paper.

The solid on the filter paper is usually washed multiple

times before being allowed to dry on the filter paper.

Decanting

To decant means to pour off the liquid from a solid.

When you decant, it is important to prevent the solid from being transferred to

the new container. It is also helpful to rinse the solid after decanting to make

sure the separation is complete.

Experiment

1. You will analyze about 5 grams of the mixture in this laboratory. Make sure to

think about what masses you need to record during this process. Remember

we are trying to quantify what percentage of the mass is SiO₂, what

percentage of the mass is NaCl, and what percentage of the mass is

C₆H₅COOH.

2. To the total mixture, add about 50 mL of distilled water and boil the water and

slurry mixture while stirring. What components will dissolve in the water?

What components will NOT dissolve in the water? Use the solubility table to

make this determination. After the water has boiled, decant the liquid into a

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Figure 2.2: Vacuum filtration

apparatus. Red tubing is

connected to vacuum line. Filter

paper is placed in white funnel.