Contact Angles and Surface Interactions Quiz
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Questions and Answers

What type of surface is characterized by strong interaction with liquid molecules, leading to dispersion rather than droplet formation?

  • Hydrophobic surface
  • Lipophilic surface
  • Oleophobic surface
  • Hydrophilic surface (correct)

What does a large contact angle indicate about the interaction between a solid and a liquid?

  • Low solid-liquid attraction (correct)
  • Equal cohesion and adhesion forces
  • High solid-liquid attraction
  • High liquid-liquid cohesion

Which of the following correctly describes the equilibrium contact angle?

  • It has no relation to the surface free energy.
  • It is always smaller than the contact angle measured with a droplet.
  • It is influenced by solid, liquid, and air interface interactions. (correct)
  • It is solely determined by the properties of the liquid.

Which statement is NOT true regarding contact angles?

<p>Contact angles are measured by the solid phase. (A)</p> Signup and view all the answers

If the contact angle is small, what does this imply about the surface properties?

<p>Good wettability of the surface by the liquid (C)</p> Signup and view all the answers

In which scenario will the liquid likely form drops on a solid surface?

<p>When the surface is hydrophobic (A)</p> Signup and view all the answers

What primarily determines the size of the contact angle formed between a liquid and a solid?

<p>Relative strength of cohesion and adhesion forces (D)</p> Signup and view all the answers

Which of the following best describes a hydrophobic surface?

<p>It leads to liquid being placed in the form of drops. (A)</p> Signup and view all the answers

What is the primary reason for the Lotus Effect observed on the lotus leaf?

<p>Surface roughness combined with hydrophobic properties (D)</p> Signup and view all the answers

Which measurement technique can be used to analyze the shape of the drop on a sample surface?

<p>High resolution camera (A)</p> Signup and view all the answers

What happens to a water drop on a super hydrophobic surface according to the Lotus Effect?

<p>It rolls over dirt particles (A)</p> Signup and view all the answers

In the contact angle experiment measuring quartz with respect to DAH concentration, what is being primarily evaluated?

<p>Behavior of liquid drops on the surface (D)</p> Signup and view all the answers

What is the approximate contact angle for a water drop on a lotus leaf?

<p>170 degrees (A)</p> Signup and view all the answers

What does a contact angle between 30 and 89 degrees indicate about a mineral's surface?

<p>The surface is partially wettable. (A)</p> Signup and view all the answers

What is the significance of the advancing contact angle being larger than the receding contact angle?

<p>It indicates contact angle hysteresis. (B)</p> Signup and view all the answers

If a mineral surface has a contact angle around 90 degrees, what can be concluded about its wettability?

<p>It is hydrophobic. (D)</p> Signup and view all the answers

What does a contact angle approaching 0 degrees suggest about a mineral surface?

<p>The surface is fully hydrophilic. (B)</p> Signup and view all the answers

What is the relationship between surface roughness and contact angle?

<p>Surface roughness can alter the wetting properties. (D)</p> Signup and view all the answers

Which option accurately describes contact angle hysteresis?

<p>It is the difference between advancing and receding contact angles. (B)</p> Signup and view all the answers

What is the effect of mineral surface heterogeneity on contact angle?

<p>It may influence the wettability of the surface. (C)</p> Signup and view all the answers

Which equation represents the equilibrium contact angle based on Young's formula?

<p>$ ext{γ}<em>{WA} = ext{γ}</em>{MA} - ext{γ}<em>{MW} + ext{γ}</em>{W} ext{. Cosθ}$ (C)</p> Signup and view all the answers

What is the primary factor that affects the flotation of mineral particles?

<p>Wetting of minerals with water (D)</p> Signup and view all the answers

Which minerals are characterized as hydrophobic and suitable for flotation?

<p>Coal and graphite (B)</p> Signup and view all the answers

What is the ideal contact angle range for effective flotation?

<p>50° &lt; θ &lt; 75° (D)</p> Signup and view all the answers

Which method is NOT commonly used for measuring contact angles?

<p>Tilted lens (D)</p> Signup and view all the answers

What is the function of collectors in the flotation process?

<p>To enhance the hydrophobicity of desired minerals (C)</p> Signup and view all the answers

Why must the buoyancy of the air bubble exceed gravity for flotation to occur?

<p>To enable the mineral to float effectively (A)</p> Signup and view all the answers

What is a super-hydrophobic surface characterized by?

<p>High contact angle with water (A)</p> Signup and view all the answers

Which equipment is primarily used to measure contact angles?

<p>Goniometer (D)</p> Signup and view all the answers

What happens at a DAH concentration of 1.10-2 M?

<p>There is no flotation occurring (C)</p> Signup and view all the answers

What is the effect of an amine concentration between 1.10-4 and 1.10-3 M?

<p>Flotation recovery can reach up to 90% (D)</p> Signup and view all the answers

Which of the following concentrations has no contact angle?

<p>1.10-2 M (C)</p> Signup and view all the answers

What is indicated by a high contact angle of approximately 70°?

<p>Sufficient amine concentration (C)</p> Signup and view all the answers

At which point is flotation recovery at its maximum?

<p>Between 1.10-4 and 1.10-3 M concentrations (D)</p> Signup and view all the answers

What does a contact angle of 0° signify?

<p>Ineffective flotation process (B)</p> Signup and view all the answers

What range of recovery percentage is typically expected at amine concentrations between 1.10-4 and 1.10-3 M?

<p>Up to 90% (B)</p> Signup and view all the answers

If flotation recovery is measured at 20%, what might be the cause?

<p>Excessive amine concentration (A)</p> Signup and view all the answers

What happens to the contact angle as DAH concentration increases from $1.10^{-6}$ M to $5.10^{-4}$ M?

<p>It increases steadily. (D)</p> Signup and view all the answers

At what DAH concentration does the flotation recovery first exceed 50%?

<p>$5.10^{-5}$ M (D)</p> Signup and view all the answers

Which DAH concentration results in the highest flotation recovery percentage?

<p>$2.10^{-3}$ M (C)</p> Signup and view all the answers

What is the contact angle associated with a DAH concentration of $1.10^{-4}$ M?

<p>54.6° (A)</p> Signup and view all the answers

Which DAH concentration has the lowest flotation recovery percentage?

<p>$1.10^{-6}$ M (D)</p> Signup and view all the answers

What relationship exists between contact angle and flotation recovery as DAH concentration increases?

<p>Both increase together. (B)</p> Signup and view all the answers

At a concentration of $1.10^{-3}$ M, what is the flotation recovery percentage?

<p>82.7% (C)</p> Signup and view all the answers

Which of the following statements is true regarding the effect of DAH concentration on the contact angle?

<p>Increased DAH concentration leads to higher contact angles. (A)</p> Signup and view all the answers

What is the contact angle at a DAH concentration of $5.10^{-3}$ M?

<p>68.4° (A)</p> Signup and view all the answers

Which DAH concentration yields a contact angle closest to 60 degrees?

<p>$2.10^{-4}$ M (A)</p> Signup and view all the answers

At what DAH concentration does the flotation recovery drop below 10%?

<p>$2.10^{-2}$ M (B)</p> Signup and view all the answers

If the flotation recovery is 64.7%, what is the corresponding DAH concentration?

<p>$1.10^{-4}$ M (A)</p> Signup and view all the answers

As DAH concentration increases from $1.10^{-5}$ M to $1.10^{-4}$ M, what happens to the flotation recovery?

<p>It increases. (B)</p> Signup and view all the answers

Flashcards

Contact Angle

The angle formed at the point where a liquid droplet meets a solid surface.

Hydrophilic Surface

A surface that attracts and spreads out liquid, like water on a clean glass window.

Hydrophobic Surface

A surface that repels liquid, causing it to form droplets, like water on a waxed car.

Cohesion Forces

Forces of attraction between molecules of the same substance.

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Adhesion Forces

Forces of attraction between molecules of different substances, like a liquid and a solid.

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Wettability

The tendency of a solid surface to be wetted by a liquid.

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Contact Angle Measurement

A measurement used to assess the wettability of a surface, typically involving an air bubble touching the surface.

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Surface Free Energy

The energy required to create a new surface, indicating the surface's stability and attraction to other substances.

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Wetting of Minerals

The tendency of a mineral to be wetted by water; a key factor in mineral processing.

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Flotation

A process where hydrophobic mineral particles attach to air bubbles in a suspension and rise to the surface.

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Hydrophobic Mineral

A mineral with a low surface energy, often used in flotation because it readily attaches to air bubbles.

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Collectors

Chemicals used to increase a mineral's hydrophobicity, making it easier to float.

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Goniometer

A device that measures the contact angle between a liquid and a solid surface, using a lens and camera.

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Sessile Drop Method

A method of measuring contact angle that involves observing a liquid droplet on a solid surface.

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Contact Angle Hysteresis

The difference between the advancing contact angle (θA) and the receding contact angle (θR) on a surface.

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Advancing and Receding Contact Angles

A surface that can have varying contact angles depending on whether the liquid is advancing (moving forward) or receding (moving backward) on the surface.

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Effect of Roughness on Contact Angle

Microscopic variations in a mineral surface that can change its wettability.

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Effect of Heterogeneity on Contact Angle

Different chemical groups present on a mineral surface can result in varying wettability.

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Hydrophobicity

The tendency of a surface to repel water, causing water droplets to form a distinct angle on the surface.

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Self-cleaning surface

A surface that allows water droplets to easily roll off, carrying away dirt and dust. This is often achieved by combining hydrophobic properties and microscopic structures.

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Hydrophobic coating

A type of coating that gives a surface similar properties to a lotus leaf, making it water-repellent and self-cleaning.

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Cohesion

The measure of how much a substance sticks to itself. Strong cohesive forces lead to liquids that are tightly packed and resistant to spreading.

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Adhesion

The measure of how much a substance sticks to another substance. Strong adhesive forces lead to liquids spreading and wetting surfaces.

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Concentration

The amount of a substance dissolved in a solution, typically expressed in moles per liter (M).

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DAH (Dodecylammonium Hydroxide)

A chemical compound used in flotation to promote the attachment of minerals to air bubbles.

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Flotation Recovery

The percentage of mineral particles removed from a solution during flotation, indicating the efficiency of the process.

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Concentration Dependence

The relationship between a substance's concentration and its effect on a process, such as contact angle or flotation recovery.

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Wettability Modification

The ability of a substance to change the wettability of a surface, allowing it to float or sink. In this case, DAH changes the wettability of quartz.

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Concentration Dependence of Wettability

The change in wettability of a surface as the concentration of DAH increases. This causes the contact angle to increase and influences the flotation recovery.

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Correlation of DAH Concentration, Contact Angle, and Flotation Recovery

The relationship between concentration, contact angle, and flotation recovery. High DAH concentrations typically lead to higher contact angles and higher flotation recovery.

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Critical Concentration

The amount of DAH needed to create a noticeable change in contact angle and flotation recovery. Here, the critical concentration is between 1.10-6 and 1.10-5 M.

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Study Notes

Surface and Colloid Chemistry

  • This presentation covers the properties of solid-liquid interfaces and surfaces, focusing on contact angles.
  • A liquid dropped onto a solid surface either spreads out or forms droplets.
  • Strong liquid-solid interactions result in the liquid spreading completely, creating a hydrophilic surface (water-loving).
  • Weak liquid-solid interactions lead to the formation of droplets, creating a hydrophobic surface (water-repellent).

Contact Angle

  • The angle formed between a liquid surface and a solid surface is the contact angle.
  • This angle is determined by the relative strengths of cohesive forces (among liquid molecules) and adhesive forces (between liquid and solid).
  • A large contact angle indicates weak adhesion forces.
  • A small contact angle indicates strong adhesion forces.
  • Contact angles are crucial for understanding how liquids interact with solid surfaces.
  • Wettability is related to the contact angle. Low angles mean good wettability and high angles mean poor wettability.
  • The contact angle is important in determining the behavior of a liquid on a solid material.

Hydrophilic and Hydrophobic Surfaces

  • Hydrophilic surfaces have low contact angles (typically less than 90°).
  • Water spreads easily on these surfaces. This means the water molecules are attracted to the solid surface more than they attract each other.
  • Hydrophobic surfaces have high contact angles (typically greater than 90°).
  • Water beads up on these surfaces. The strength of water-water attraction is greater than the water-solid attraction.

Contact Angle Hysteresis

  • Contact angles are not constant. They often vary depending on whether the liquid is advancing or receding on the surface.
  • Contact angle hysteresis exists when the advancing angle is significantly different from the receding angle.

Effect of Roughness and Heterogeneity

  • Surface roughness and chemical heterogeneity can influence contact angles.
  • They can affect the apparent contact angle measurement.

Contact Angle Measurement Methods

  • Different methods exist for measuring contact angles, including sessile drop, sessile bubble, captive bubble, and tilting plate methods.
  • A goniometer is a common instrument used for contact angle measurement.
  • It uses light, lenses, and video cameras and sample positioning.

Contact Angle and Flotation

  • Flotation is a technique used in mineral processing to separate desired minerals from unwanted materials.
  • Hydrophobic minerals attach to air bubbles, enabling their separation from the liquid phase. This separation process works because of the different contact angles the different minerals have with water.
  • Minerals with large contact angles tend to float better.

Lotus Effect

  • The lotus effect describes self-cleaning properties observed on lotus leaves, which are based on surface roughness and hydrophobic waxes.
  • This effect demonstrates how surface microstructures, combined with the right material, result in very low contact angles, enabling the ease of water-shedding and self-cleaning.

Measuring Advancing and Receding Contact Angles

  • Techniques such as the add/remove volume method using instruments like DROPimage Advanced and the ramé-hart Automated Dispensing System can be used.

Theta Optical Tensiometer

  • The Theta Optical Tensiometer is an instrument used for contact angle measurement.
  • It contains features involving introduction, contact angle analysis, pendant drop measurement, and meniscus measurement.

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Surface and Colloid Chemistry PDF

Description

Test your knowledge on contact angles and surface interactions in this engaging quiz. Explore concepts such as hydrophobic surfaces, the Lotus Effect, and the implications of contact angle measurements in materials science. Perfect for students studying physics or chemistry.

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