Science Revision

Light 

Total Internal Reflection

• When light is completely reflected back at a boundary between two mediums 

• Occurs when light meets a less dense medium at an angle of incidence larger than the critical angle 

Critical Angle

• Angle of incidence which causes the angle of reflection to be 90 degrees

Food Tests 

Benedict Test (reducing sugars):

• Original colour- blue 

• Positive Test- orange/brick red 

Iodine Test (starch):

• Original colour: orange/brown

• Positive Test: blue/black 

Biuret Test (protein):

• Original colour: blue 

• Positive Test: violet/purple 

Ethanol Teste (lipids):

• Shows cloudly emulsion forming 

Acids, Bases and Salts 

• Acid has a pH of less than 7 

• A salt is formed when the metal ions replace the hydrogen ions in and acid

Acids and Metals 

•  Only metals that are above hydrogen in the reactivity series will react with dilute acids 

• When a dilute acid reacts with a metal a salt and hydrogen are formed 

Acid and Bases

• Metal oxides and metal hydroxides act as bases 

• When an aid and base react, neutralisation occurs, forming water 

• When an acid reactions with a metal oxide, salt and water ar formed 

• When an acid reacts with a metal hydroxide, salt and water is formed 

Acids and Carbonates

• When an acid reacts with a metal carbonate, a salt, water and carbon dioxide are formed 

Litmus

• Acid turns blue litmus turns red  

Methyl Orange 

• When an acid is added, methyl orange turns red 

• Aqueous solutions of acids contains H+ ions 

• Aqueous solutions of alkalis contain OH- ions 

PH scale

• 0 very acidic 

• 14 very alkaline 

• Acids have a high concentration of hydrogen ions 

• Alkali have a low concentration of of hydroxide ions 

• Neutral solutions have a ph of 7

Universal indicator

• yellow/orange/red indicate acidity 

• blue/violet indicate alkalinity 

• Neutral solutions will show as green 

Define 

• Acids are known as proton donors (release hydrogen ions)

• Bases are known as proton acceptors (accepts hydrogen ions)

• A proton is the same as a hydrogen ion

• A strong acid completely disassociates in aqueous solution

• A weak acid is an acid that only partially dissociates in aqueous solution 

• HCL is a strong acid 

• Ethanoic acid is a weak acid