Crystal Formation Methods

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Questions and Answers

What is the reason for the formation of crystals during homogeneous nucleation and growth?

  • The rate of precipitation increases suddenly
  • The extent to which the ions are soluble decreases when the pH changes in the right direction (correct)
  • The material that precipitates becomes more soluble
  • The solvent begins to evaporate rapidly

What is the result of evaporation on the solution?

  • An increase in the availability of solvent for the ions
  • No change in the solvent availability
  • A state of undersaturation
  • A state of super saturation (correct)

What is the advantage of very careful crystallization?

  • It is a cheap method of crystallization
  • It is the best method of preparing materials that are extremely pure (correct)
  • It produces crystals quickly
  • It produces crystals of varying purity

What is the phenomenon where compounds can crystallize with different crystal structures?

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

What is the importance of polymorphism in industrial manufacturing?

<p>It is a major issue in industrial manufacturing (B)</p> Signup and view all the answers

What is the primary driving force for drying in convective or direct drying?

<p>Reduced air relative humidity (A)</p> Signup and view all the answers

What is the limitation of applying high temperatures in convective or direct drying?

<p>Product quality considerations (D)</p> Signup and view all the answers

What is affected by the rate of precipitation?

<p>The purity of the crystal (A)</p> Signup and view all the answers

What is the purpose of reducing pressure in supercritical drying?

<p>To lower the boiling point (B)</p> Signup and view all the answers

What is the advantage of freeze drying in preserving biological properties?

<p>It retains vitamins and bioactive compounds (C)</p> Signup and view all the answers

What is the characteristic of natural air drying?

<p>It takes advantage of unheated forced air (A)</p> Signup and view all the answers

What is the consequence of using too hot air in convective or direct drying?

<p>Crust formation or case hardening (A)</p> Signup and view all the answers

What is the primary reason why evaporation occurs faster in areas of less pressure?

<p>There is less exertion on the surface, allowing molecules to escape (D)</p> Signup and view all the answers

What is the effect of a larger surface area on the rate of evaporation?

<p>It increases the rate of evaporation (B)</p> Signup and view all the answers

What is the relationship between the density of a substance and its rate of evaporation?

<p>Higher density results in slower evaporation (C)</p> Signup and view all the answers

What is required for boiling to occur?

<p>A combination of heat and reduced pressure (D)</p> Signup and view all the answers

What happens when molecules collide during the evaporation process?

<p>Energy is transferred and the molecules may gain enough to escape (C)</p> Signup and view all the answers

Why don't the molecules in a glass of water typically turn into vapor quickly?

<p>They lack the energy to escape (D)</p> Signup and view all the answers

What factors need to be considered when devising a strategy for drying grains?

<p>Air temperature, relative humidity and moisture content (B)</p> Signup and view all the answers

What is the typical result of increasing the internal energy of a solid substance?

<p>A rise in its temperature to its melting point (B)</p> Signup and view all the answers

What is the term for a substance that has undergone a complete phase change from solid to liquid?

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

What is the relationship between the melting point and freezing point of a pure crystalline solid?

<p>The melting point is often equal to the freezing point (B)</p> Signup and view all the answers

What is the effect of increasing pressure on the melting point of a substance?

<p>It lowers the melting point (C)</p> Signup and view all the answers

What is the relationship between the strength of intermolecular forces in a crystal and its melting point?

<p>Weaker forces result in a lower melting point (D)</p> Signup and view all the answers

What is viscosity a measure of in a fluid?

<p>Its resistance to deformation at a given rate (C)</p> Signup and view all the answers

What did Isaac Newton postulate about the shear stress between layers in a fluid?

<p>It is directly proportional to the velocity gradient (A)</p> Signup and view all the answers

Why is close temperature control essential in viscosity measurements?

<p>To ensure accurate measurements of lubricants (D)</p> Signup and view all the answers

What happens to the viscosity of a liquid as its temperature increases?

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

What happens to the viscosity of a gas as its temperature increases?

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

What happens to the cohesive forces between molecules in a liquid as it is heated?

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

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