Chemistry C1

Cooking food

Cooking food causes a chemical change to occur:

• New substances are formed
• There is an energy change
• It can't be reversed easily

Eggs and meat contain proteins which denature when heated. This causes the texture and appearance to change.

Potatoes are plants so they have a rigid cell wall. During cooking this is broken down and the cells become soft, starch grains swell up and are released so your body can digest them.

Emulsifiers

Emulsifiers are used to mix oil and water. Hydrophilic head= water loving. Hydrophobic tail= water hating. The hydrophilic head attracts water whilst the hydrophobic tail attracts oil.

Baking powder

Baking powder contains sodium hydrogen carbonate. When it's heated, it decomposes to make sodium carbonate and water, some carbon dioxide is given off:

2NaHC03 ----> Na2CO3 + H20 + CO2

Perfumes

Properties:

• Evapourates easily so it can travel to your nose
• Non toxic
• Non irritant
• Doesn't dissolve in water
• Doesn't react with water

Perfumes are volatile so they can evapourate easily. Molecules have a weak force of attraction so it doesn't require much energy to overcome this.

Describing solutions:

• Soluble substances are substances tha dissolve in a liquid
• Insoluble substances do not dissolve in a liquid
• A solvent is the liquid into which a substance is dissolved
• The solute is the substance that gets dissolved
• A solution is what you get when you mix a solvent and a solute

Solvents

• Nail varnish doesn't dissolve in water because the attraction between the molecules in nail varnish is stronger than the attraction between water and nail varnish molecules.
• The attraction between the molecules in nail varnish is stronger than the attraction between water and nail varnish molecules.

Testing perfumes

Advantages of animal testing

• It prevents humans from being harmed

Disadvantages of animal testing

• It's cruel to animals
• Animals don't have the same body chemistry as humans

Paint

Paint is a colloid where the particles are mixed and dispersed with particles of a liquid but aren't dissolved.

Paint is a mixture of

• Pigment
• Binding medium
• Solvent

Emulsion paints are water based.

Paints can be used to protect or decorate. It coats the surface with a thin layer and dries when the solvent evapourates. Oil paints dry when the solvent evapourates and the oil is oxidised by atmospheric oxygen.

Special pigments:

• Coating kettles and cups
• Mood rings
• Toys for babies

Phosphorescent pigments glow in the dark. Energy is absorbed during the day and then released when it's dark.

Acrylic paints can be added to thermochromic pigments to make the paint change more colours. Phosphorescent pigments aren't radioactive and therefore are safe to use.

Choosing a fuel:

• Engery value- How much energy is released?
• Availability
• Ease of storage
• Cost
• Toxicity
• Pollution
• Ease of use

Complete combustion:

• Fuels burn with O2
• Blue flame
• CH4 + 2O ---> CO2 = 2H20

Incomplete combustion:

• Fuels burn without O2
• Yellow flame
• Soot is produced
• 2CH4 + 3O2 ---> 2CO + 4H2O
• CH4 + O2 ---> O + 2H2O

The atmosphere today:

• 21% Oxygen
• 78…