Surface tension

Protocol for measuring the surface tension coefficient

using Traube’s stalagmometer

Materials:

• Traube’s stalagmometer
• Two detergent solutions with following densities: 1050 kg/m^3 si 1070 kg/m^3
• Distilled water, density: 1000 kg/m^3; surface tension coefficient: 73 x 10^-3 N/m
• Timer, marker
• Three Berzelius beakers

Procedure:

A. Measuring the number of drops for a fixed volume (between the upper and the lower mark):

1. select two marks on the stalagmometer tube (first mark above the glass bulb and second mark below to the glass bulb)
2. place the lower part of the stalagmometer in a Berzelius beaker with distilled water
3. using the attached rubber bulb absorb the distilled water until the upper mark
4. let the first drop to flow into the beaker (it will be counted)
5. count the all of the drops till the meniscus of distilled water reaches the lower mark

Obs: there are no ideal situations when the meniscus will stop exactly to the upper or lower mark

6. perform nine measurements for distilled water

7. repeat the previous steps for the other two detergent solutions

8. write your results in a table:

9. reorganize the working place

B. Calculate the surface tension coefficients

1. calculate the mean, standard deviation and standard error mean for all investigated liquids
   1. calculate the surface tension coefficients using the formula: γ_x = γ₀ (ρ n₀)/ (ρ₀ n)
      1. γ_x = surface tension coefficient for a solution of detergent
      2. γ₀ = surface tension coefficient for solvent (distilled water)
      3. ρ_x = density of the detergent solution
      4. ρ₀ = density of the solvent (distilled water)
      5. n_x = no of drops for the detergent solution
      6. n₀ = no of drops for the solvent (distilled water)
   2. state one-two conclusions related to your results