Gravity Filtration

Gravity filtration is a laboratory method used to separate a solid residue from a liquid filtrate by passing the mixture through filter paper held in a funnel. The technique allows suspended solids to be collected while the clear liquid passes through.

1. Set up a ring stand with a ring clamp and place a funnel over a receiving flask. Use a clay triangle if needed to support the funnel.
2. Position the flask so its neck touches the funnel tip to reduce splashing.
3. Insert filter paper into the funnel. Use fluted filter paper by unfolding it so the folds touch the funnel, or prepare a flat disc by folding it twice with a slight angle and tearing a small corner to help it fit smoothly.
4. Wet the filter paper with deionized water so it adheres to the funnel walls.
5. Pour the liquid mixture down a glass rod into the funnel, ensuring the rod touches the funnel wall to prevent splashing. Keep the funnel filled to about two-thirds.
6. Continue pouring before the funnel empties, rinsing any residue from the glass rod into the funnel.
7. Transfer any remaining solid with a rubber policeman or a wash bottle to ensure complete collection.
8. Rinse the solid on the filter paper with small amounts of water, letting it drain between washes.
9. Once filtration is complete, carefully remove the filter paper. The solid left behind is the residue, while the clear liquid collected is the filtrate.

Demonstration of Filtration - Rugby School Chemistry:

📄 Filtration by Gravity - Valencia College: https://science.valenciacollege.edu/chemistry/techniques/tech16-filtrationgravity.pdf

• Use vacuum (Büchner) filtration for faster separation when fine particles or large volumes are involved.
• Test different types of filter paper (fluted, plain, or pre-weighed) depending on the experiment’s requirements.

• Wear safety goggles and a lab coat to protect from splashes.
• Handle glassware carefully to avoid breakage and cuts.
• Use caution with the wash bottle to prevent over-spraying liquids.
• Dispose of residue and filtrate according to laboratory waste guidelines.

• Why is it important to wet the filter paper before filtering? (It seals the paper against the funnel, preventing solids from bypassing the filter.)
• What is the difference between residue and filtrate? (Residue is the solid left on the filter paper; filtrate is the liquid that passes through.)
• Why should the tip of the glass rod touch the funnel wall while pouring? (It prevents splashing and loss of material.)
• How does fluted filter paper improve the filtration process? (It increases surface area and allows liquid to pass more quickly.)