21.2.3 Aluminum Flashcards Preview

AP Chemistry > 21.2.3 Aluminum > Flashcards

Flashcards in 21.2.3 Aluminum Deck (13)
Loading flashcards...
1
Q

Aluminum

A
  • Aluminum forms many minerals. Bauxite is an important aluminum mineral.
  • Aluminum is purified through the Bayer process and the Hall-Héraoult process.
  • Gallium, in gallium arsenide, is an important light-emitting semiconductor.
2
Q

note 1

A
  • Aluminum is the most abundant metal found in the
    lithosphere. Only oxygen (a nonmetal) and silicon (a
    metalloid) are more common.
  • Aluminum forms many minerals, several of which include other metals.
  • Bauxite is composed of aluminum oxides and other oxides (such as ferric oxide and silicon dioxide). Bauxite is an important source of aluminum.
  • The Bayer process is used to purify aluminum from bauxite. In the first step of the Bayer process, bauxite is heated with hydroxide (OH – ). The iron precipitates out, and the silicon dioxide and aluminum enter solution.
  • In the second step, the solution is cooled. The aluminum hydroxide precipitates out, leaving the silicon hydroxides in solution.
  • Heating aluminum hydroxide yields alumina (Al 2 O 3 ).
    Alumina is used to make aluminum metal.
  • Because of its large heat of formation ( H f ), aluminum
    metal requires a huge amount of energy to produce.
  • Before 1886, aluminum chloride was reduced with a
    potassium amalgam:
  • AlCl 3 (s) + 3K(Hg) x (l) -> 3KCl(s) + Al(Hg) x (l)
  • This reaction required a great deal of heat, but allowed the aluminum to be separated from the mercury by distillation.
  • In 1886, Hall and Héraoult discovered that alumina dissolves in cryolite (Na 3 AlF 6 ) at 950°C. This allows electrolysis of alumina to be carried out at a much lower temperature than the melting point of alumina (950°C versus 2050°C).
3
Q

note 2

A
  • Aluminum has many household and industrial uses, such as aluminum cans, drain cleaners, catalytic converter supports, and aluminum foil.
  • Even though aluminum is an excellent reducing agent,
    aluminum cans and foil do not oxidize to a great extent.
    Aluminum forms a thin coating of Al 2 O 3 , which binds to the aluminum and protects it from further oxidation through a process called passivation. This protective layer is not like rust (ferric oxide), which flakes off iron after forming.
  • Gallium arsenide (GaAs) is a semiconductor that gives off light.
  • Gallium arsenide is commonly found in light-emitting diodes (LEDs).
  • Aluminum is used to dope gallium arsenide diodes, giving different colors.
4
Q

Which of the following substances does not contain aluminum?

A

Apatite

5
Q

Which of the following describes the role of cryolite in the Hall-Héroult process?

A

Cryolite serves as the electrolyte and solvent in the reaction.

6
Q

Which formula for an aluminum compound is incorrectly matched with its application?

A

AlCl3 / flocculating agent

7
Q

Although aluminum is a strong reducing agent, aluminum cans do not “rust”. Why?

A

Aluminum oxide creates a protective coating.

8
Q

Arrange the steps of the Bayer process of alumina production (from bauxite) in the correct order:

  1. Al(OH)4- -> Al(OH)3 + OH-
  2. Al(OH)3 + OH- -> Al(OH)4-; Al(O)OH + OH- + H2O -> Al(OH)4-
  3. Al(OH)3 (heated) -> Al2O3 + H2O
  4. AlCl3 + 3K(Hg)x(l) -> 3KCl(s) + Al(Hg)x(l)
A

2, 1, 3

9
Q

Which of the following is the most abundant metal in the lithosphere?

A

Aluminum

10
Q

All of the following compounds are amphoteric except:

A

CaO

11
Q

Which of the following aluminum ores contains aluminum and no other metals?

A

Corundum

12
Q

Which of the following statements regarding the Group 13 elements is false?

A

They form only 3+ cations

13
Q

Which would not have been a use of aluminum prior to 1886?

A

Cookware such as pots and pans

Decks in AP Chemistry Class (338):