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Surface tension of water by the capillary tube method

Surface Tension Of Water By The Capillary Tube Method

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Introduction to the Surface Tension of Water by the Capillary Tube Method

Surface Tension is a property of a liquid surface displayed by its acting as if it were a stretched elastic membrane. This phenomenon can be observed in the nearly spherical shape of small drops of liquids and of soap bubbles.

Because of this property, certain insects can stand on the surface of water. The high surface tension of water is caused by strong molecular interactions.

The surface tension arises due to cohesive interactions between the molecules in the liquid. At the bulk of the liquid, the molecules have neighboring molecules on each side.

Aim Of The Surface Tension Of Water By The Capillary Tube Method

To measure the surface tension of water by capillary tube method.

Tools Of The Surface Tension Of Water By The Capillary Tube Method

  • Three glass capillary tubes – one of medium diameter, one larger, and one smaller.
  • Dilute nitric acid
  • Dilute caustic soda solution
  • Travelling microscope or glass scale
  • Rubber bands
  • Beaker
  • Stand and clamp
  • Thermometer

Steps And Method of The Experiment

  • Clean the three capillary tubes, beaker, and glass scale with nitric acid, tap water, caustic soda, and finally tap water.
  • Select the medium-bore capillary tube and attach a bent pin using a rubber band.
  • Fix the tube vertically in a clamp with its lower end immersed in water.
  • Move the tube slightly down and return it to its original position to ensure proper wetting.
  • Adjust the bent pin until its tip just touches the water surface.
  • Focus the travelling microscope on the bottom of the meniscus and record the reading .
  • Mark the meniscus position, remove the beaker, and focus the microscope on the bent-pin tip. Record the reading .
  • Cut the capillary at the marked position and measure its internal diameter , taking the mean of two perpendicular measurements.
  • Repeat the procedure for the other two capillary tubes.
  • Record the temperature of the water.

Capillary Tube Method Surface Tension Experiment: Theory

Parameters & Final Law

γ
Surface tension
N m⁻¹
d
Diameter of the capillary tube
m
h
Height of water inside the capillary tube
m
ρ
Density of water = 1000
kg m⁻³
g
Gravitational acceleration = 9.8
m s⁻²
Final Law
Surface Tension γ = ¼ dhρg

Table of The Readings

Table of the Readings

d1 d2 d = d2 − d1 h1 h2 h = h2 − h1
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Medical Application For Surface Tension Of Water By The Capillary Tube Method

In medicine, surface tension measurement is above all used in connection with various pathological states of lung surfactants such as adult respiratory distress syndrome, bronchial asthma, and pneumonia.

Frequently Asked Questions About the Surface Tension of Water by the Capillary Tube Method

What does surface tension of water by the capillary tube method actually measure?

It quantifies how strongly water molecules cling together at the liquid's surface, using the height water rises in a narrow tube — a direct, measurable consequence of that cohesive force pulling against gravity.

Why are three different capillary tube diameters used?

Testing multiple tube widths lets you confirm that the calculated surface tension stays consistent regardless of tube diameter, which validates the underlying formula rather than relying on a single measurement.

Why is lung surfactant deficiency such a serious medical problem?

Without enough surfactant to lower surface tension in the alveoli, the small air sacs tend to collapse after each breath, forcing the lungs to work much harder to reinflate — a major factor in conditions like ARDS and, in premature infants, respiratory distress syndrome.