Surface and Colloid Chemistry Quiz
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Questions and Answers

What property of the lotus leaf is primarily responsible for the Lotus Effect?

  • Thickness of the leaf structure
  • High transparency of the leaf
  • Chemical composition of the leaf
  • Surface roughness and hydrophobic properties (correct)

When analyzing the shape of a drop placed on a sample surface, which method is NOT mentioned as a valid analysis technique?

  • Ultrasonic measurement (correct)
  • Visual inspection by eye
  • Photographic analysis
  • Using a high resolution camera

Which of the following best describes the movement of water drops on a lotus leaf?

  • They evaporate quickly
  • They form puddles on the surface
  • They roll over dirt particles (correct)
  • They absorb into the leaf

What measurement is used to understand the hydrophobic properties of surfaces in the contact angle experiment?

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

What results from the different microstructures on the lotus leaf?

<p>Enhanced self-cleaning properties (C)</p> Signup and view all the answers

What term is used for surfaces that attract water molecules, resulting in liquid dispersion?

<p>Hydrophilic surfaces (B)</p> Signup and view all the answers

What results from a weak interaction between liquid molecules and a solid surface?

<p>The liquid forms droplets on the solid surface (D)</p> Signup and view all the answers

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

<p>Low solid-liquid attraction forces (C)</p> Signup and view all the answers

Which of the following correctly describes the behavior of a liquid as characterized by contact angle?

<p>Contact angle can be affected by molecular interactions (B)</p> Signup and view all the answers

How is the degree of wetness of a mineral quantified?

<p>Using the contact angle (D)</p> Signup and view all the answers

What happens to the contact angle as the cohesive forces among liquid molecules increase compared to adhesive forces?

<p>The contact angle increases (B)</p> Signup and view all the answers

Which of the following best describes the role of contact angle in surface analysis?

<p>It measures the surface's energy characteristics (A)</p> Signup and view all the answers

What is the contact angle measured against when observing a solid surface?

<p>The liquid phase (C)</p> Signup and view all the answers

What role does wetting play in mineral processing methods such as flotation?

<p>Wetting facilitates the attachment of hydrophobic particles to air bubbles. (B)</p> Signup and view all the answers

Which factor is essential for effective flotation of a mineral?

<p>The contact angle should be between 50o and 75o. (B)</p> Signup and view all the answers

Which mineral is likely to be classified as hydrophobic and suitable for flotation?

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

What is one of the primary purposes of adding collectors in the flotation process?

<p>To enhance the attachment of air bubbles to desired minerals. (A)</p> Signup and view all the answers

What equipment is primarily used for measuring contact angles?

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

How does a large contact angle affect the flotation of a mineral?

<p>It helps hold air bubbles more effectively to the mineral. (A)</p> Signup and view all the answers

Which contact angle measurement method involves observing a liquid drop on a solid surface?

<p>Sessile drop method (D)</p> Signup and view all the answers

Why is it important for non-wetting particles to attach to air bubbles in flotation?

<p>It enables the separation of desired minerals from the mixture. (A)</p> Signup and view all the answers

What is the maximum flotation recovery achieved with sufficient amine concentration?

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

What is the contact angle associated with high flotation recovery?

<p>70 degrees (B)</p> Signup and view all the answers

What occurs when there is excessive amine concentration?

<p>Flotation recovery decreases to 0% (C)</p> Signup and view all the answers

At which concentration of DAH is no flotation observed?

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

Which situation describes having a high flotation recovery?

<p>Sufficient amine concentration and high contact angle (D)</p> Signup and view all the answers

What is the flotation recovery percentage when the contact angle is 0 degrees?

<p>0% (A)</p> Signup and view all the answers

What is the expected flotation recovery with a contact angle near 70 degrees?

<p>90% (C)</p> Signup and view all the answers

Which concentration range of DAH results in high flotation recovery?

<p>1.10-4 to 1.10-3 M (A)</p> Signup and view all the answers

What does a contact angle between 0 and 30 degrees indicate about a solid surface?

<p>It is wettable. (C)</p> Signup and view all the answers

Which of the following statements about contact angles is true?

<p>Hydrophilic surfaces have low contact angles. (B)</p> Signup and view all the answers

What is contact angle hysteresis primarily related to?

<p>The change in contact angle during the spreading and receding of a droplet. (C)</p> Signup and view all the answers

If a liquid on a mineral displays a contact angle of around 90 degrees, what can be inferred about the mineral?

<p>The mineral is hydrophobic. (B)</p> Signup and view all the answers

Which factor does NOT influence the contact angle on a mineral surface?

<p>Temperature of the surrounding air. (B)</p> Signup and view all the answers

What is an example of a hydrophilic surface characteristic?

<p>Complete dispersion of droplets. (A)</p> Signup and view all the answers

What is the effect of molecular dynamics simulation on contact angles?

<p>It provides real-time observations of droplet behavior. (D)</p> Signup and view all the answers

Which contact angle range indicates a surface is partially wettable?

<p>30 to 89 degrees. (A)</p> Signup and view all the answers

What is the contact angle for a DAH concentration of $2.10^{-3}$ M?

<p>72.3° (A)</p> Signup and view all the answers

Which DAH concentration results in the highest flotation recovery?

<p>2.10-3 M (B)</p> Signup and view all the answers

At which DAH concentration does flotation recovery begin to significantly decline?

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

Identify the contact angle corresponding to a DAH concentration of $5.10^{-6}$ M.

<p>29.7° (D)</p> Signup and view all the answers

What contact angle is observed at a DAH concentration of $5.10^{-4}$ M?

<p>65.2° (B)</p> Signup and view all the answers

What trend is observed in contact angle as DAH concentration increases?

<p>Contact angle increases. (C)</p> Signup and view all the answers

What is the flotation recovery percentage at a DAH concentration of $1.10^{-4}$ M?

<p>64.7% (C)</p> Signup and view all the answers

Which of the following concentrations gives a contact angle closest to 40°?

<p>$2.10^{-5}$ M (D)</p> Signup and view all the answers

What is the flotation recovery percentage at the lowest concentration of $1.10^{-6}$ M?

<p>15.6% (D)</p> Signup and view all the answers

What is the observed flotation recovery at a DAH concentration of $2.10^{-4}$ M?

<p>75.2% (C)</p> Signup and view all the answers

For a DAH concentration of $1.10^{-3}$ M, what is the contact angle?

<p>70.1° (B)</p> Signup and view all the answers

How does flotation recovery change from $1.10^{-6}$ M to $1.10^{-5}$ M?

<p>Increases by approximately 9% (D)</p> Signup and view all the answers

At a DAH concentration of $2.10^{-2}$ M, what is the flotation recovery percentage?

<p>9.7% (D)</p> Signup and view all the answers

Flashcards

Contact Angle

The angle formed between a liquid surface and a solid surface when a liquid is placed on the solid.

Hydrophilic Surface

A material that allows a liquid to spread across its surface. This happens when the attraction between the liquid and solid is stronger than the attraction between liquid molecules.

Hydrophobic Surface

A material that resists the spread of a liquid. The attraction between the liquid molecules is stronger than the attraction between the liquid and solid.

Cohesion Forces

The attraction forces between liquid molecules, causing them to stick together.

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Adhesion Forces

The attraction forces between liquid molecules and a solid surface causing the liquid to adhere to the solid.

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Wettability

A measure of how much a solid surface can be wetted by a liquid. A large contact angle indicates a material is not easily wetted.

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Surface Free Energy

A measure of the energy stored in the surface of a material. It determines how a material interacts with other materials.

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Contact Angle Measurement

A measure of wettability of a mineral. It's measured by the angle between the mineral surface and a bubble touching the mineral.

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Young's Equation

A formula used to calculate the equilibrium contact angle, describing the balance of forces between the surface tensions of the liquid-air, liquid-solid, and solid-air interfaces.

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Contact Angle Hysteresis

The range of contact angles observed as a liquid droplet advances or recedes on a solid surface. The difference between the maximum (advancing angle) and minimum (receding angle) is called hysteresis.

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Effect of Roughness on Contact Angle

The microscopic irregularities or bumps present on a mineral surface can affect the contact angle, making the surface appear more or less wettable.

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Effect of Heterogeneity on Contact Angle

The presence of different chemical components on a mineral surface can lead to variations in wettability and contact angles.

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Lotus Effect

The ability of a surface to repel water and allow water droplets to roll off, leaving the surface clean. This is due to the surface's microscopic structure and its hydrophobic properties.

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Super Hydrophobic surface

A surface that repels water, causing water droplets to form spherical shapes and roll off easily.

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Hydrophobic Coating

A compound used in surface coatings to create water-repellent properties, mimicking the Lotus Effect.

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Self-cleaning surface

The phenomenon where a water droplet placed on a surface takes up dust particles as it rolls, keeping the surface clean.

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Hydrophobic mineral

A mineral that repels water and prefers to attach to air bubbles, making it suitable for flotation.

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Hydrophilic mineral

A mineral that attracts water and prefers to stay in the water suspension, making it unsuitable for flotation.

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Flotation

A process used to separate valuable minerals from other materials by using air bubbles to float the desired minerals to the surface.

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Collector

A chemical added to a mineral during flotation to make it more hydrophobic, increasing its tendency to attach to air bubbles.

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Buoyancy force

The ability of a bubble to overcome the weight of a mineral particle and lift it to the surface during flotation.

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Gravity force

The force that pulls a mineral particle down towards the bottom of the flotation cell.

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Cohesion

The force of attraction between liquid molecules that causes them to stick together.

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Adhesion

The force of attraction between liquid molecules and a solid surface that causes the liquid to adhere to the solid. A high adhesion force means the liquid is attracted to the solid.

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Dodecylamine Hydrochloride (DAH)

A chemical compound used in mineral processing to increase the hydrophobicity of mineral surfaces, thereby promoting flotation.

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Flotation Recovery

The percentage of target minerals that are successfully separated from a mixture using flotation.

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Correlation of Quartz-Amine Adsorption / Contact Angle / Flotation

The relationship between the concentration of DAH and the contact angle and flotation recovery of quartz.

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Insufficient DAH Concentration

A concentration of DAH where there is insufficient amine to significantly change the wettability of quartz, resulting in low flotation recovery.

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Low Contact Angle and Flotation Recovery Range

The range of DAH concentration between 1.10-6 and 1.10-5 M where the contact angle of quartz is low and flotation recovery is weak.

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Surface Modification

The process of applying a chemical treatment to mineral surfaces to enhance their hydrophobicity for flotation.

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Quartz

A mineral that is commonly targeted in flotation due to its valuable economic properties.

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Mineral Processing

The study of mineral processing techniques, particularly focusing on flotation processes.

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What is the relationship between amine concentration and contact angle?

The contact angle is influenced by the amine concentration. Low concentrations increase the contact angle, leading to higher recovery rates. However, excessive concentrations lead to a 0° contact angle and no flotation.

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What is quartz-amine flotation?

Quartz-amine flotation is a process used to separate quartz from other minerals. It relies on the difference in wettability between quartz and other minerals.

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What is the effect of a low amine concentration on quartz-amine flotation?

A low amine concentration (1.10^-4 - 1.10^-3 M) is optimal, leading to a high contact angle (~70°). This results in high flotation recovery, up to 90%.

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What happens when you use an excessive amine concentration in quartz-amine flotation?

An excessive amine concentration (1.10^-2 M) does not allow for any contact angle formation, resulting in zero flotation recovery, meaning none of the quartz is separated effectively.

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What is the contact angle?

The contact angle is a measure of the wettability of a mineral surface, and its value depends on the balance of forces related to the liquid-air, liquid-solid, and solid-air interfaces.

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What does the contact angle tell us about wettability?

A higher contact angle indicates lower wettability, meaning the liquid does not spread easily across the surface. A low or zero contact angle shows high wettability, where the liquid will readily spread across the surface.

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Why is the contact angle important in quartz-amine flotation?

In the case of quartz-amine flotation, the contact angle is crucial, as it determines how much the amine solution will adhere to the quartz surface. A higher contact angle means a stronger attraction between quartz and amine.

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Why is a low contact angle a problematic factor in quartz-amine flotation?

A low contact angle in quartz-amine flotation is a serious issue, as it means the amine solution spreads easily across the quartz surface, not allowing for effective flotation.

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Study Notes

Surface and Colloid Chemistry

  • Deals with properties of solid-liquid interfaces and surfaces, specifically contact angles.
  • Examines how liquids behave on solid surfaces, either dispersing or forming drops.
  • The contact angle, formed between the liquid surface and the solid, is influenced by the cohesive forces within the liquid and adhesive forces between the liquid and the solid surface.
  • Hydrophilic surfaces exhibit strong liquid-solid interactions, resulting in complete liquid dispersion. Water-loving.
  • Hydrophobic surfaces have weak interactions, leading to droplets. Water-repellent.
  • Contact angle size depends on the balance of attraction forces (cohesion and adhesion) between molecules in the liquid and between the liquid and the solid.
  • Larger contact angles signify weaker solid-liquid attraction, while smaller angles indicate stronger attraction.
  • Wettability, a measure of how well a solid surface can be wetted by a liquid, is determined by the contact angle.
  • Contact angles between 0-30 degrees are considered wettable, 30-89 degrees partially wettable, and greater than 90 degrees non-wettable.

Molecular Dynamics Simulation (MDS)

  • Used to simulate the behavior of a liquid drop on hydrophilic and hydrophobic surfaces.
  • Simulations illustrate different wetting behaviors on these surfaces. Hydrophilic surfaces result in drops spreading, while hydrophobic surfaces result in drops forming spherical shapes.

Contact Angle and Flotation

  • Wetting of minerals is a key parameter in mineral processing (e.g., flotation).
  • Flotation separates minerals based on their hydrophobicity or hydrophilicity.
  • Hydrophobic minerals tend to attach to air bubbles, allowing for separation from hydrophilic minerals.
  • A greater contact angle often equates with improved flotation recovery. Higher contact angles will aid in separating hydrophobic materials from the rest.
  • Chemicals (collectors) can alter mineral surface properties to control the contact angle.
  • The buoyancy of the air bubble needs to be greater than the gravity force affecting the mineral.

Lotus Effect

  • Lotus effect is based on surface roughness and hydrophobic properties.
  • Lotus surfaces demonstrate self cleaning.
  • Water droplets roll off, carrying dirt and debris along with them, due to the hydrophobic nature.

Contact Angle Measurement Methods

  • Goniometry is an optical tensiometer used to measure contact angles (simplest method)
  • Various techniques such as sessile drop, sessile bubble, captive bubble, and tilting plate methods are utilized for contact angle measurements.
  • The shape of the drop, formed on the surface, can be evaluated visually, or captured via high-resolution camera photographs.

Θeta Optical Tensiometer

  • Provides several measurements including contact angles and pendant drop analysis.

Advancing and Receding Contact Angles

  • Contact angles can differ depending on whether the liquid is advancing or receding.
  • Advancing contacts are larger, while receding are smaller than the average contact angle.

Effect of Roughness and Heterogeneity

  • Roughness and heterogeneity in mineral surfaces can affect contact angles.
  • Different chemical groups can exist on a surface, impacting wettability.

Contact Angles of Selected Substances

  • A table lists contact angles for diverse substances, such as PTFE and metals like gold, silver.

Contact Angle Experiment

  • Studies contact angles relating to DAH concentration on quartz samples
  • Experimental data tables show contact angles measurements.
  • Correlation exists between flotation recovery and contact angle variations with DAH concentration.

Lab 3

  • Explores Contact Angle experiments.
  • Scheduled for December 6, 2024 (9:00-11:20).

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Surface and Colloid Chemistry PDF

Description

Test your knowledge on surface and colloid chemistry, focusing on the properties of solid-liquid interfaces and contact angles. Understand how hydrophilic and hydrophobic surfaces affect liquid behavior and learn about the forces that dictate wettability.

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