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T8 Acids and Bases - Coggle Diagram
T8 Acids and Bases
Acid deposition: refers to the precipitation of any acid, can be either dry or wet
dry refers to acid gases and solid particles
wet refers to acid rain, snow and fog
Distinction between natural rain and acid rain:
- natural rain is acidic with a pH of 5.6, this is due to the presence of CO2 within the atmosphere
- acidic rain has a pH below 5, and is usually due to the presence of sulfur dioxide and nitrogen odixes, which react with water to form sulfuric acid and nitric acid
How this happens: 
The 4 acids produced from these processes (nitric acid, nitrous acid, sulfuric acid, sulfurous acids) are all stronger than carbonic acid and can bring the pH of rain down to a 2.
Impact on:
- buildings: many buildings use limestone, which reacts with acidic rain therefore wreaking and eroding the building , rusting of steel , iron or aluminum is also increased by the presence of the ions in acid rain
- fish , under 5.5 pH most fish cannot survive and prevent fish eggs from hatching, the aluminum ions are leeched from the soil by acid rain, where they cause fish gills to secrete excess mucus around the gills, leading to death
— loss of species can create a chain reaction of death
- aluminum in the soil is released when the pH falls, too much damages the roots of plants, preventing them from taking up water
- humans : causes respiratory issues, by affecting the mucous membranes and lungs
Pre and post combustion methods to reduction acidity:
- pre: refining/ removing sulfur from coal or petroleum
— example: hydrodesulfurisation: gets sulfur out of petroleum , through a process requiring lots of heat and pressure and a catalyst
- post: removing sulfur oxides
— example: flue gas desulfurization , pass gas into scrubber which sprays a combo fo CaO and CaCO3
as lime stone CaCO3 can neutralize acids
Bronsted- Lowry theory:
acids are proton(H+) donors
basaes are proton(H+) acceptors
these protons refer to the H+ ion however it is more likely to exist as a H3O+ ion in an aqueous solution
Following this logic all BL acids must have a H as they need to donate, and all BL base must have a pair of lone electros to accept the H
Conjugate acid-base pairs: are corresponding substances in an equilibrium reaction, they differ only by one proton (H+)
for example, NH3 is a conjugate acid base pair of NH4 for amphiprotic species it is important to determine when it is the acid and when it is the base. NOTE: if it is acid on left side, it must create the conjugate base on the right sideto find Base, minus 1 proton, to find acid, add 1 protonUsually, Acids have an H whereas bases are OH, but if an H is bonded to a metal then it is more likely to be basic
Protisim:
- amphiprotic (only works in terms of bronsted Lowry theory): substance can act as both an BLA and BLB, due the the existence of an H ion and a pair of lone electrons, which is why water is amphiprotic
— may be confused with amphoteric, but all amphiprotic are amphoteric but not all amphoteric are amphiprotic
- there are also terms to describe the number of hydrogens an BLA can donate:
— monoprotic: one proton
—diprotic: two
— triprotic: three
Examples of common acids: Examples of common bases:
pH + strength of acids
pH is used to measure the concentration of hydrogen ion in a solution and is determined using the equation:
- pH is inversely related to [H+], meaning that the higher the [H+] the lower the pH and vice versa. Conversely, the higher the [OH-] the higher the pH
- thus the concentrations of [OH-] and [H+] Can be used to determine the pH of the substance,
— when [OH-] = [H+], netural
— when [OH-] > [H+], basic
—when [OH -] < [H+] ,acidic
- scales: the ratio between change in pH compared to change in [H+] concentration, is very large, i.e. it increases by 10 fold each time,
i.e. if i went from pH4 -> 5, the ion concentration of [OH-] increases 10 fold compared to 5
pH = x, then conc of [H+] = 1 x 10^-x
Calculating pH:
- you really only need these two equations:
and this one for pOH, which is the same thing but in terms of the OH the pOH + pH = 14 at 25C
Measuring pH:
- litmus paper (qualitative):
— red paper turns blue when in base
— blue paper turns red when in acid
more Common ones:
- methyl orange: red for acid, yellow for base
-phenolphthalein: colorless for acid, pink/purple for alkali
universal indicatior (quantitative):
- a mixture of indicators to give a range of colors representing the differing pH’s
but the most reliable way is to use a pH probe and meter that more accurately measeus pH
Autoionisation of water:
Water :
The equilibrium constant can be switched into form Kw, which is the ionic product of water has the value of 1 x 10^-14 at temperatures of 25C, which is represented like this:
And at certain temperatures [OH-] and [H+] are constants, meaning that if [H+] increases, [OH-] must decrease and vice versa, i.e. they must add to the same amount.
does dissociate to a very small extent, and can be represented by the following equation
The strength of acids and bases depends on the degree of disassociation, i.e. the extent to which the acid will all turn into ions when reacted with water
NOTE: concentration is not the same as strength, can have high conc but low strength and vice versa
Strong acids:
- all will disassociate, meaning that if there are x moles of the acid there will be x mole of the ion
- full dissociation therefore one way arrow
- organic acids are usually weak, therefore , the Kc will lie to the far left, meaning only a small amount is dissociated, hence the use of the equilibrium arrow
Strong bases:
- all will disassociate in to. OH- ions, all metal hydroxides except the ones in group 1 and 2 metals are weak bases
- as they are weak, the Kc will be on the far left, Kc value will be small, some weak examples of bases would be ammonia and amines
How to tell if it is strong acid or base: Conjugate acids and bases:
- if an acid is strong, then the conjugate base is weak, and vice versa, same thing in terms of the base and conjugate acid.
this is becasue a strong acid is very willing to donate a proton, meaning that the H+ is very easily to be broken, a bond that is easily broken is hard to form again, therefore the conjugate base formed only weakly can form a bond with the proton
Lewis acids and bases theory:
The idea that acids are electron pair acceptors
bases are electron pair donor
the Lewis theory is much broader and more recent then the Bronsted Lowry threory, therefore all Lewis acids. Bases are BL acids or bases but the reverse cannot is false
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