when is it appropriate to use gravity filtration and when to use vaccume filtration
Vacuum (note the correct spelling) is used when time is important OR when gravity filtration is far too slow and complete separation is not necessary. However, for most quantitative work, vacuum filtration is appropriate only when using a filter integrated with the holder; i.e., a Buckner type funnel and filter paper allows too many of the solid particles to pass. Integrated filters, such as Selas crucibles, in which the correct porosity filter is sealed into the porcelain crucible can be used for quantitative work with BaSO4, AgCl, and other ppts. Older type vacuum filters that were made with macerated filter paper vacuumed onto perforated metal back plates can be used also but those have been almost completely supplanted with the more modern porcelain type.
In chemistry and laboratory settings, gravity filtration and vacuum filtration are used for separating solids from liquids. The choice between the two techniques depends on the characteristics of the mixture you are working with.
Gravity filtration is typically used when the liquid you are filtering is easily drained under the influence of gravity alone. This method involves pouring the mixture into a funnel with filter paper or a porous material called a filter medium. The liquid passes through the filter medium and collects in a container beneath the funnel, while the solid particles are retained on the filter.
On the other hand, vacuum filtration is employed when the liquid takes longer to filter due to a high viscosity or when a faster filtration rate is desired. Vacuum filtration utilizes a Büchner funnel, which is connected to a vacuum source. The vacuum creates a pressure difference, allowing the liquid to be pulled through the filter medium more quickly. This method is especially effective for separating large volumes of solids from liquids.
In summary, the appropriate filtration technique depends on the properties of the mixture you are dealing with. If the liquid drains easily by gravity, gravity filtration is suitable. If the liquid is more viscous or you need faster filtration, vacuum filtration should be used.