Experiment - 1: Determination of Surface Tension by drop weight method PDF

# Experiment - 1: Determination of Surface Tension by drop weight method ## Aim: Determine the surface tension of a given liquid at room temperature by stalagmometer method. ## Theory: - **Cohesive forces**: forces that exist between molecules of one phase. - **Adhesive forces**: forces that exist...

# Experiment - 1: Determination of Surface Tension by drop weight method ## Aim: Determine the surface tension of a given liquid at room temperature by stalagmometer method. ## Theory: - **Cohesive forces**: forces that exist between molecules of one phase. - **Adhesive forces**: forces that exist between molecules of two different phases. The cohesive forces among liquid molecules are responsible for the phenomenon of surface tension. In the bulk of the liquid, each molecule is pulled equally in every direction by neighboring liquid molecules resulting in a net force of zero. The molecules of the liquid surface have no other molecules on all sides of them and therefore are pulled inward. This creates some internal pressure and forces liquid surfaces to contract to the minimal area. - **Surface Tension**: is the force per unit length (dyne/cm) that must be applied parallel to the surface so as to counterbalance the net inward pull of molecules of interface together. - **Stalagmometer**: consists of a dropping tube with a capillary, the end of which is flattened. This flattened end helps to give a wider dropping surface. This surface is already ground flat and polished. The other end of the capillary is sealed on a tube of thicker bore, containing a bulb. There are two marks etched on this ## Observation Table: Liquid | W1 | W2 | W2(average) | m1 = W2-W1 | Y = γ1m1 | ------- | -------- | -------- | -------- | -------- | -------- | Water | 122.79 | 123.799 | 123.989 | 10 | 72 dyne/cm | | 124.09 | 124.178 | | | 0.128g | | ## Table 2 Liquid | W1 | W2 | W2(average) | m2 = W2-W1 | Y2 = γ1m2 | ------- | -------- | -------- | -------- | -------- | -------- | Sample B | 123.569 | 123.78 | 123.56 | 0.86g | 48 dyne/cm | Sample (1%) | 122.78 | 123.449 | 123.7g | 0.97g | 54.56 dyne/cm | Sample (3%) | 122.79 | 123.769 | 123.079 | 0.097g | | | 122.9 | 123.689 | 123.579 | | | | ## Apparatus: Stalagmometer, rubber tubing with a screw clip, 50ml beaker, distilled water. ## Procedure: 1. The stalagmometer is cleaned with chromic acid and then with distilled water. 2. Take distilled water in a beaker, Suck the water through the tube of stalagmometer till the water rises above the mark A with the help of rubber tubing attached at the top using screw clip. 3. Weigh on empty, clean and dry small beaker (W1). Should hold vertically, and to help drops to fall. 4. Add 10 drops of water. 5. While adding the drops of the liquid: - Weigh the beaker with 10 drops of water (W2). - Repeat steps 3, 4 & 5 three times and calculate the average weight of one drop (m1). M1 = W2-W1 / 10 6. Repeat steps 1- 5 for the provided sample using the same pipette and beaker (washed with alcohol and dried) and calculate the surface tension of the sample using the equation - - Y2 = m2 / m1 where: - Y1 = surface tension of water (known) - Y2 = surface tension of the sample (unknown) - m1 = mass (weight) of one drop of water - m2 = mass (weight) of one drop of sample ## Result: The surface tension of the sample increases with increases in their concentrations. **Precautions:** - Use distilled water. - Pipette should be held vertically while adding the drops of liquid. - Pipette and beaker should be washed with alcohol and dried. ## Description of the image: The document is a handwritten chemistry lab report on the determination of surface tension of a liquid using a stalagmometer. There are a few hand-drawn diagrams, including a diagram of the set up for measuring surface tension, a diagram of a stalagmometer, and a table of observations.