3.4 Acids Flashcards
pH scale
< 7 is acidic
= 7 is neutral
> 7 is alkaline
Universal indicator
Acidic = Yellow - Red Neutral = Green Alkaline = Light Blue - Purple
Methyl Orange Indicator
Acidic = Red Neutral = Yellow Alkaline = Yellow
Phenolphthalein Indicator
Acidic = Colourless Neutral = Colourless Alkaline = Pink
Red Litmus Indicator
Acidic = Red Neutral = (stays) Red Alkaline = Blue
Blue Litmus Indicator
Acidic = Red Neutral = (stays) Blue Alkaline = Blue
Percentage of gas in Air: Oxygen
21%
Percentage of gas in Air: Nitrogen
78%
Percentage of gas in Air: Argon
0.96%
Percentage of gas in Air: Carbon Dioxide
0.04%
Practical: Measuring percentage of oxygen
Use a syringe and react oxygen with copper, once all has been added to metal, use the equation:
Decrease in vol
——————— X 100
Initial Volume
To find the percentage of oxygen
How to find the percentage of oxygen
React it with another element (usually a metal)
What has happened if practicle for oxygen percentage doesn’t work?
The metal wasn’t heated for long enough or there’s a leak in the apparatus
Element combustion
When an element reacts with oxygen to produce an oxide
Element + Oxygen = Element Oxide
Combustion: Non metal
Non-metal turns to a Non-Metal Dioxide that is a Gas (Acidic)
Combustion: Metal
A metals turns into a metal oxide that is solid (Alkaline)
Important Combustion: Magnesium
2Mg(s) + O2 —> 2MgO(s)
Observations: Bright white light and white powder formed
Important combustion: Sulphur
S(s) + O2 (g) —> SO2 (g)
Observations: Blue flame
Important combustion: Hydgrogen
2H2 + O2 —> 2H2O
Observations: Squeaky pop
Test for oxygen
Glowing splint in x gas, if it relights, oxygen is present
Dissolving Oxides: Metal
Metal oxides form alkaline solutions
Dissolving Oxides: Non-metal
Non-metal dioxides form acidic solutions
How to determine if an unknown element is metal or non-metal
- Combust it in oxygen
- Dissolve the oxide/dioxide
- Check the pH with an indicatior