16.2 application of oxidation-reduction reactions

16.2 Application of Oxidation-Reduction Reactions——Redox in Photography

Group member:Carol; Frank; Nick; Alice; Joe; Taylor

Enjoy this original technology

PREPARE——some special tool

A container for liquid which is used to develop film. It must keep out of the light.

Developing tank

Obscura

Something to know• Until 1838, the French inventor L.J.M Daguerre fixed the

image in a camera on highly polished, silver-plated copper to make the first photograph.

• These early photographs were called daguerreotype in his honor.

• The polished silver surface of a daguerreotype gives a feeling of presence where the image appears to be floating in space.

• The image is formed on the surface of the silver plate (resembling the surface of a mirror) and is unstable; it can easily be rubbed off and will oxidize in the air, so from the outset daguerreotypes were mounted in sealed cases or frames with a glass cover.

Background • The daguerreotype was the first commercially

successful photographic process.

• The raw material for plates was called Sheffield plate, plating by fusion or cold-rolled cladding and was a standard hardware item produced by heating and rolling silver foil in contact with a copper support.

• Depending on the angle viewed, and the color of the surface reflected into it, the image can change from a positive to a negative

Theory • Modern photographic film is made of

a plastic backing covered with a layer of gelatin.

• The reaction begins when the shutter on a camera is opened.

Theory • Light from the scene being photographed passes through

the camera’s lens and shutter and strikes the light-sensitive silver bromide on the film.

• The light energy causes electrons to be ejected from a few of the bromide ions, oxidizing them to elemental bromine.

• The electron are transferred to silver ions, reducing them to metallic silver atom.

• In areas where the light is brightest, more grains are activated, and after developing, they become the darker area.

Manipulation The developer reduces all the silver ions to silver atoms in any grain of silver bromide that was hit by light.

AgBr(s)+2S₂O₃²⁻(aq) →[Ag(S₂O₃)₂]³⁻(aq)+Br⁻(aq)

Manipulation The fixed film is washed to remove any remaining developer or fixed solution.

When light is shone through the negative onto light-sensitive photographic paper, a photographic print is made.

Thank you!