Atmosphere and acids - 3.4

an indicator is a substance that changes colour to tell you about the pH of a soluti9on

methyl orange - acidic colour = red - neutral colour = yellow - alkaline colour = yellow phenolphthalein - acid colour = colourless - neutral colour = colourless - alkaline colour = pink

red litmus - acidic colour = red - neutral colour = red - alkaline colour = blue blue litmus - acidic colour = red - neutral colour = blue - alkaline colour = blue

nitrogen - 78% oxygen - 21% argon - 0.96% carbon dioxide - 0.04%

when an element reacts with oxygen to produce an oxide

1 - Magnesium magnesium + oxygen –> magnesium oxide 2 - Sulphur sulphur + oxygen –> sulphur dioxide 3 - Hydrogen hydrogen + oxygen –> hydrogen oxide (water)

Fe 2+

Ag +

Fe 3+

Zn 2+

Cu 2+

Pb 2+

glowing splint –> relights This is because the oxygen allows the wood in the splint to combust more efficiently

oxides tend to form a acid or alkaline solution depending on whether the original element was metal or non-metal metal –> alkaline solution non-metal –> acid solution

• combust it in oxygen • dissolve the oxide formed • check the pH of the solution with an indicator

H+ donor

H+ acceptor

OH- donor

HCl

HNO3

H2SO4

H3PO4

H2CO3

NaOH