chemical reaction in the presence of light

Workout time• Pour the solution in the small beaker into the big beaker, stir

and observe.

• Filtrate the solution using filter paper and collect the residue.

• Put one of the residue under the light and another in dark cupboard. Observe the changes a few minutes later.

Chemical reactions that occur in the presence of Light

Why?

Because…

• These materials have chemicals that are sensitive to light

• When they exposed to light, a chemical reaction occurs

• These substances are

photosensitive chemicals

Photosynthesis

• Photo-Light; Synthesis- to produce something• Photosynthesis: a natural process that occur in

the presence of light• Plants need light to make their own food

Photosynthesis

• Chlorophyll :green pigments found in plants• Chlorophyll absorbs light energy from the sun

to enable chemical reaction to occur during photosynthesis

Carbon dioxide + Water ----> glucose + oxygen

• Glucose is stored in plant as starch, starch in leaf is detected by iodine

Light

Chlorophyll

Iodine test

Blue black coloured ---> starch exist

Let’s proof it!!!

• Silver Chloride1. Pour 50 cm3 sodium chloride solution into a beaker.2. Add about 10 cm3 silver nitrate solution.3. Divide the mixture into two beakers and filtrate the

solution.4. Collect the residue, put one in a dark cupboard and

the other out in the bright light.5. After a few minutes, examine the contents of the

two beakers.

What is the variables that are:

• Manipulated?• Responding?• Constant?

What is the variables that are:

• Manipulated: the presence of light (place that the beaker is stored)

• Responding: the changes of the filtrate• Constant: Time, Volume, Concentration

Observation

• When silver nitrate solution is added to sodium chloride solution, _________________ formed

• After a few minutes, the silver chloride that is exposed to the sun_________________ while the silver chloride keep in dark ____________

Observation

• When silver nitrate solution is added to sodium chloride solution, white precipitate is immediately produced.

Silver nitrate + Sodium chloride --- > Silver chloride

• After a few minutes, the silver bromide that is exposed to the sun turned greyish while the silver bromide kept in dark remained unchanged.

Effect of Light on Silver Bromide

• Silver bromide or silver chloride is a photo sensitive chemical

• When exposed to light, the compound will decompose into silver and bromide

Silver bromide ---> Silver + Bromide Silver chloride ---> Silver + Chlorine

Light

Purplish Black or grey colourLight

Storage of Photosensitive Chemicals

• Dark bottles: photosensitive chemical solution• Photographic films or paper: black box or

black bag• Opaque plastic bottle: bleaching agent that

have chlorine

Word Puzzle

Matching

Workbook time ^ _ ^