39 Questions
What is 'r' in the context of surface tension?
Radius of the capillary tube
In what units is the radius of the capillary tube measured?
cm or m
What is the relationship between the radius of the capillary tube and the surface tension?
The radius of the capillary tube is inversely proportional to the surface tension
What is the condition for the surface tension to be measured in N/m?
The radius of the capillary tube is in cm or m
What is the unit of surface tension when the radius of the capillary tube is measured in cm?
N/m
What happens to surface tension when impurities increase?
It decreases
What is the main function of surfactants?
To decrease the surface tension of a liquid
At what interface do surfactants adsorb to reduce surface tension?
Liquid-solid interface
Why do surfactants reduce surface tension?
By decreasing the cohesive forces between molecules
What is the result of impurities on the cohesive forces between molecules?
They decrease the cohesive forces
What is the effect of surfactants on the surface of a liquid?
They make it easier for the liquid to spread out
What is the relationship between impurities and surface tension?
Impurities decrease surface tension
What is the effect of impurities on the surface tension of a liquid?
It decreases the surface tension
What is the primary function of surfactants in relation to surface tension?
To reduce the surface tension of a liquid
Where do surfactants adsorb to reduce the surface tension of a liquid?
At the liquid-solid interface
What is the result of the adsorption of surfactants at the liquid-solid interface?
Decreased cohesive forces between molecules
What is the impact of impurities on the cohesive forces between molecules at the surface of a liquid?
They decrease the cohesive forces between molecules
At what temperature is the surface tension of water calculated in the given problem?
300°C
What is the method described in the text used to determine the surface tension of a liquid?
Drop weight method
What is the density of water in the given problem?
996 kg/m³
What is the acceleration due to gravity in the given problem?
9.81 m/s²
What is the radius of the capillary tube in the given problem?
0.002 m
What is the surface tension of water in the given problem?
71.18 × 10⁻³ N/m
What is the angle of convexity of the liquid in the given problem?
45 degrees
What is the purpose of a stalagmometer?
To measure the surface tension of a liquid
What is a stalagmometer composed of?
A capillary tube with a bubble
What can be used in the same way as a stalagmometer?
A pipette
What is the function of a device mentioned in the text?
To measure the surface tension of a liquid
What type of tube is used in a stalagmometer?
A capillary tube
The contact angle θ is nearly zero for non-wetting liquids.
False
Cos 0 is equal to 0.
False
The contact angle θ is a measure of surface tension.
False
Water is an example of a non-wetting liquid.
False
The value of cos θ is dependent on the type of liquid.
True
The surface tension values of two different liquids can be compared using the same capillary tube.
True
The masses of the two drops are not determined in this method.
False
The capillary tube is used to mix the two liquids together.
False
The surface tension values of the two liquids are compared by measuring the volume of the two drops.
False
The same capillary tube is used to compare the surface tension values of multiple liquids.
True
Study Notes
Surface Tension
- Surface tension arises from cohesive forces between liquid molecules.
- In the bulk, molecules interact equally with each other in all directions.
Units of Surface Tension
- Units of surface tension: N/m and dynes/cm.
- Surface tension coefficient (γ) unit: dynes/cm or N/m.
Measurement of Surface Tension
- Methods to measure surface tension:
- Liquid rise in capillary tube method
- Drop weight method
- Pubble pressure method
- Using a tensiometer device
Liquid Rise in Capillary Tube Method
- Prepare a capillary tube with a known radius (r) and immerse one end in the liquid.
- Measure the height of the liquid inside the capillary tube (h).
- At a certain height, the liquid stops rising, and the liquid is under the influence of two forces:
- Surface tension forces (pushing the liquid upwards)
- Gravitational forces (pulling the liquid downwards)
- Equation: γ = (ρ * g * h) / (2 * cos(θ))
Factors Affecting Surface Tension
- Temperature: surface tension decreases with increasing temperature
- Impurities: surface tension decreases with increasing impurities
- Surfactants: surfactants lower the surface tension of a liquid by adsorbing at the liquid-solid interface and reducing the cohesive forces between molecules
Additional Key Facts
- Surface tension pressure: the pressure exerted by a liquid on its surface (Pa)
- Contact angle (θ): for wetting liquids (such as water), it is nearly zero and (cos 0 = 1)
- Surface tension can be compared between two different liquids (γA, γB) using the drop weight method
Test your understanding of surface tension, a phenomenon that occurs due to the cohesive forces between liquid molecules. This quiz covers the interactions between molecules in the bulk and their behavior at the surface. Get ready to dive into the world of liquids and their properties!
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