Surface Tension of Water By Capillary Rise Method: Explanation

Surface Tension of Water is the tension of the surface film of a liquid that is caused by the attraction of the particles by the bulk of liquid which minimizes the surface area. Surface tension is what allows items with a higher density than water, such as razor blades and insects, to float on a water surface without even becoming partially buried. At 20 °C (68 °F), water has a surface tension of 0.07275 joules per square meter. Organic liquids with lower surface tensions, such as benzene and alcohols, have a lower surface tension than mercury, which has higher surface tension. 

Also Check: Semiconductor Diode

Key Terms: Surface Tension, Capillary Rise, Liquid Surface, Joules, Water, Organic Liquids, Thermometer

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Aim

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Using the capillary rise method to calculate the surface tension of water.

Also check: Potential Energy

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Apparatus or Materials Required

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A travelling microscope, clamp and stand, a fine motion adjustable height stand, a flat bottom open dish, clean water in a beaker, and a pointed pointer clamped in a metallic plate with a handle, a fine motion adjustable height stand, a flat bottom open dish, and a thermometer.

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Theory

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As per considering the theory

⇒ Surface Tension, \(T = {{r (h + r / 3)\rho g} \over 2cos\theta}\)

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Diagrams

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Surface Tension by Capillary Rise

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Procedure

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Setting up the apparatus:

1. Place the adjustable height stand on the table and use levelling screws to make the base horizontal.
2. Fill an open dish with dirt-free, grease-free water and place it on top of the stand.
3. Take three different radii capillary tubes (ranging from 0.05 mm to 0.15 mm).
4. Clean and dry the capillary tubes before clamping them in order of increasing radius on a metallic plate. After the third capillary tube, clamp a pointer.
5. Clamp the metallic plate's horizontal handle in a vertical stand so that the capillary tubes and pointer are upright.
6. As a result, alter the height of the metallic plate so that the capillary tubes in the open dish dip in the water.
7. Adjust the pointer's position such that the tip of the pointer just touches the water's surface.

Measurement of Capillary Rise:

1. For both the horizontal and vertical scales, find the lowest count of the travelling microscope. Make a note of it in your notebook.
2. Raise the microscope to a comfortable working height, with the axis horizontal and pointing at the capillary tubes.
3. Placing the microscope in front of the first capillary tube is a good idea (which has maximum rise).
4. Make the horizontal crosswire slightly touch the centre area of the concave meniscus, which will seem convex under the microscope.
5. Take note of the vertical scale reading for the position of the microscope.
6. Place the microscope in front of the second capillary tube and move it horizontally.
7. Repeat the previous steps and lower the microscope.
8. The previous steps should be repeated for the third capillary tube.
9. Lower the stand so that the tip of the pointer is visible.
10. Bring the microscope in front of the pointer by moving it horizontally.
11. Lower the microscope until the horizontal cross wire is in contact with the pointer's tip.

Measurement of the Internal Diameter of the Capillary Tube:

1. Place the first capillary tube on the adjustable stand horizontally.
2. Focus the microscope on the water-soaked end. A white circle (inner bore) will be visible, encircled by a green circular strip (glass cross-section).
3. At A, bring the horizontal cross-wire into contact with the inner circle. On the vertical scale, take note of the microscope reading.
4. Raise the microscope to the point where the horizontal cross-wire touches the B circle. Take note of the reading (the difference gives the vertical internal diameter AB of the capillary tube).
5. Make the vertical cross wire meet the inner circle at C by moving the microscope on a horizontal scale. On the horizontal scale, take note of the microscope reading.
6. Rotate the microscope to the right until the vertical cross-wire touches the D circle. Take note of the reading (the difference gives the horizontal internal diameter CD of the capillary tube). Steps a to f should be repeated for the other two capillary tubes.
7. Take note of the temperature of the water in the dish.
8. Make a note of your observations in the space provided.

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Observations

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The least count of a traveling microscope (L.C.) is...........cm.

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Calculations

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As per the Formula, we can determine that:

Now, after putting the values of h and r for each capillary tube respectively, and then determing the value of T (in Dynes cm^-1).

Thus, to find the Mean Value:

\(T = {{T_1 + T_2 + T_3} \over3}\) = … dynes cm^-1.

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Result

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Therefore, the Result is:

⇒ At t°C, the surface tension of water is........ dyne cm^-1.

Precautions

Some of the important precautions include:

1. Grease should be kept out of the capillary tube and the water.
2. Set the capillary tube vertically.
3. To minimize backlash errors, the microscope should only be moved in a downward direction.
4. The internal diameter of a capillary tube should be measured in two directions that are mutually perpendicular.
5. It's important to keep track of the water's temperature.

Sources of Error

Grease may be present in the water and capillary tube.

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Previous Year Questions

1. There are two liquid drops of different radii … [JIPMER 1999]
2. Two circular plates of radius … [BITSAT 2010]
3. A soap bubble of radius r is blown up to form a bubble of radius 2r … [VITEEE 2009]
4. The radii of the two columns in a U - tube are … [AP EAPCET 2004]
5. The surface tension of soap solution is … [BITSAT 2008]
6. An ice-cube of density … [JIPMER 2005]
7. A large number of liquid drops each of radius r coalesce … [VITEEE 2018]
8. The length of a needle floating on water is 2.5 cm … [AMUEEE 1998]
9. A capillary tube of radius r is dipped inside a large vessel of water … [CBSE Class XII]
10. Two capillary tubes A and B of diameter … [KEAM 2015]
11. Kerosene oil rises up in a wick of a lantern because of … [VITEEE 2017]
12. Two mercury drops (each of radius r) merge to form a … [VITEEE 2017]
13. A big water drop is formed by the combination of … [JEE Advanced 2017]
14. Water rises to a height of 10 cm in a capillary tube and mercury … [AP EAPCET]
15. With the increase in temperature, the angle of contact … [BITSAT 2019]
16. Water rises in a capillary upto a extension height … [JIPMER 2003]
17. A capillary tube of radius r can support a liquid of weight … [JIPMER 2003]

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Things to Remember

• The surface tension is referred to as the ability of a liquid to stay in its fixed shape. 
• For instance, the drop of oil tries to remain in a spherical shape when it falls; this is the case in surface tension.
• It is when we experiment with a capillary tube, we observe that a liquid rises in a capillary tube, and the weight of the column of the liquid of density ρ inside the tube is supported by the upward force of surface tension that is acting along the circumference of the points of contact.
• The apparatus required for the experiment are, a travelling microscope, clamp and stand, a fine motion adjustable height stand, a flat bottom open dish, clean water in a beaker, a pointed pointer clamped in a metallic plate with a handle, a fine motion adjustable height stand, a flat bottom open dish, and a thermometer.

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