I used a filter paper that was too large for the Hirsch funnel and had to
fold it up around the edges. Why is it bad to fold the edges of the paper?
One reason is that it is difficult to "seal" the paper for a proper vacuum to be pulled. Another is that solid may creep onto the the other side (the underneath side) of the paper.
Folding the edges of a filter paper when using a Hirsch funnel can have a couple of negative effects.
Firstly, when you fold the paper, it becomes difficult to properly seal the edges against the funnel. This can prevent a proper vacuum from being pulled through the system. Vacuum filtration relies on a tight seal between the paper and funnel to ensure efficient filtration. If there are gaps or folds in the paper, air can escape and disrupt the vacuum, affecting the filtration process.
Secondly, folding the paper can cause a phenomenon called "solid creep". This occurs when the solid being filtered starts to accumulate or creep onto the underneath side of the paper. Solid creep can lead to contamination of the filtrate, compromising the purity of the desired substance.
To avoid these issues, it is generally recommended to use a filter paper that fits the Hirsch funnel properly without any need for folding or modification. This ensures a secure seal and avoids the potential for solid creep, allowing for effective and uncontaminated filtration.