Acids and Bases

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A2 Level mind map AQA acids and bases

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Created by sadieburgess0 almost 6 years ago
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Acids and Bases
1 Calculating the pH of strong acids
1.1 A mono-protic acid donates one mole of protons per mole of acid eg: HCl--> H+ + Cl-
1.1.1 a diprotic acid donates 2 moles of proton per mole of acid eg: H2SO4 --> 2H+ + SO4(2-)
1.2 Strong acids fully dissociate and have more H+ ions
1.2.1 to calculate the pH we use : pH-log[H+] and [H+]=10(-pH)
2 Bronsted-Lowry theory
2.1 an acid is a proton donor where as a base is a proton acceptor
2.1.1 some substances are Amphoteric eg H2O, they can act as an acid or a base depending on the reaction
2.2 an acid-base reaction is the direct transfer of a proton from an acid to a base
2.3 if calculating pH to concentration for diprotic DIVIDE by 2, if calculating concentration to pH TIMES by 2
3 Kw (=10 to the -14)
3.1 the ionic product of water: Kw-[H+][OH-]
3.1.1 has the units mol-2dm6
3.1.2 Kw increases as temperature increases because its an endothermic process this causes the pH to decrease because an increase in temperature causes equilibrium to shift to the right, increasing the yield of H+ and OH- therefore decreasing the pH (when subbed into equation)
4 Calculating the pH of strong bases
4.1 mono basic- accepts one mole of H+ per mole of base eg: NaOH
4.1.1 dibasic- accepts 2 moles of H+ per mole of base eg: Ba(OH)2
4.2 we need to find the OH- ion then use Kw/OH- to find [H+]
4.2.1 For dilutions. find how much the volume has changed by and apply this to the concentration of OH- first.
4.2.2 for a reaction between a strong acid and a strong base: calculate moles of each, find which is in excess and by how much, calculate conc of excess and find pH accordingly
5 Weak Acids
5.1 partially dissociate
5.2 in order to determine the pH we need to find H+ we use Ka= [H+][X-]/[HX]
5.2.1 therefore to calculate the [H+] =square root of {Ka[HX]}
5.3 weak acid and strong base
5.3.1 for every mole of OH- added, one mole of HA is used up and one mole of A- is formed calculate the moles of HX and OH, see which is in excess. if HA is in excess: use table to work out how much HA and A- is in excess, divide each of the mol by the total vol to find concentration. sub into [H+]= Ka x [HA] / [A-]. then sub this answer into pH=-log 10[H+} if OH- is in excess,calculate [OH], then Kw/ [OH] (Kw is 10-14). sub into pH=-log[H+]
6 pH curves and indicators
6.1 indicators are weak acids so this occurs in solution: HIn <> H+ + In-
6.2 in order to be useful, HIn and In must have different colours
6.2.1 the equivalence point shows exactly the same amount of acid and base, the indicator which goes through the equivalence point is the suitable one.
6.2.2 what makes a good indicator? the colour change must be easily observed and colour change must be easy
7 Buffer Solutions
7.1 solutions which can resist change in acidity or alkalinity
7.1.1 by keeping [OH-] and [H+} almost unchanged
7.2 Acidic Buffers- made in one of 2 ways
7.2.1 mixing a weak acid and the salt of that acid A- + H+ --> HA (so HA increases when A- decreases
7.2.2 by partly neutralising weak acid with a strong alkali HA + OH- --> H2O + A- (HA decreases as A- increases)
7.3 Basic buffers
7.3.1 Acid to the buffer removes H+ so NH3+ H+ --> NH4+
7.3.2 add alkali removes OH- so NH4+ + OIH---> H2O + NH3
7.4 see notes in book for buffer reactions.

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