Acids and Bases Flashcards
What is a Brønsted-Lowry acid?
a proton donor
What is a strong Brønsted-Lowry acid?
a fully dissociated proton donor
What is the equation for a strong acid?
HX (aq) –> H+(aq) + X- (aq)
What are examples of strong acids?
HCl, HNO3, H2SO4 (diprotic)
What is the equation for a weak acid?
HX (aq) ⇌ H+(aq) + X- (aq)
What are examples of weak acids?
carboxylic acids
Mono, di, and triprotic examples?
-carboxylic acids
-dicarboxylic acids
-H3PO4
What are Brønsted-Lowry bases?
proton acceptors
What are strong Brønsted-Lowry bases?
every base particle will accept/gain a proton
What are weak bases?
NH3, Mg(OH)2, Ca(OH)2
What are strong bases?
NaOH. (Sr(OH)2, Ba(OH)2
What are weak Brønsted-Lowry bases?
only some particles accept/gain a proton
What is pH?
pH = -log [H+]
How do you calculate [H+]?
[H+] = 10 ^ -pH
What is a property of water?
it is very weakly dissociated
What is the equation for water?
H2O(l) ⇌ H+(aq) + -OH(aq)
Which way does the equilibrium for water lie?
wayyyyy to the left
What type of reaction is the dissociation of water?
endothermic because energy is required to break O-H bonds
Why is water neutral?
[H+] = [-OH]
Why don’t we include [H20] in the equation?
because the [H20] is virtually constant
Why does the pH of water increase as temperature increases?
equilibrium shifts to the right to oppose the increase in temperature, which causes an increase in [H+], meaning pH decreases/lowers
What is Kw?
Kw = [H+] [-OH] - the ionic product of water
What is Kw at room temp?
1.00 x 10 ^-14
What is Kw when you have [H+]?
[H+] = √Kw
How do you calc the pH of a weak acid?
Ka = [H+] [HA-] / [HA] , [H+] = √ Ka x [HA] , pH = -log[H+]
How do you calc the pH of a strong base?
Kw = [H+] [-OH] , [H+] = Kw / [-OH] , pH = -log[H+]
Calc the pH of a SASB solution?
-mol acid
-mol base
-excess moles
-[H+] = excess moles / TOTAL volume
-pH = -log[H+]
What is an indicator?
a substance which changes colour over a narrow pH range
Talk about phenolpthalein
protonated —— pH 9 —— deprotonated
colourless —— —— —— pink
Talk about methyl orange
protonated —— pH 4 —— deprotonated
red —— —— —— —— yellow
What are the 4 types of pH curves?
SASB, WASB, SAWB, WAWB
What makes something a strong acid on a graph?
starts below pH = 2
What makes something a weak acid on a graph?
starts above pH = 2
What makes something a strong base on a graph?
ends above pH = 12
What makes something a weak base on a graph?
ends below pH = 12
Where is v-equivalence on a graph?
where the straight part goes down
Where is half equivalence on a graph?
halfway to where the straight part goes down
What indicator for SASB?
phenolphthalein and methyl orange as both change colour on the vertical part of the graph
What indicator for WASB?
phenolphthalein
What indicator for SAWB?
methyl orange
What indicator for WAWB?
neither, must use a pH probe instead as no clear vertical part of the graph
What is a buffer solution?
a solution that can resist changes in pH, an addition of small amounts of acid/alkali/water upon dilution
Acidic buffers have a pH of…
less than 7
What are acidic buffers?
a mixture of weak acid and it’s salt, ie. ethanoic acid and sodium ethanoate
How do you make an acidic buffer?
-mix ethanoic acid and sodium ethanoate
or
-mix excess ethanoic acid and NaOH (cheaper)
Name 3 uses of buffers?
-making dyes
-intravenous injections
-shampoo
How do acidic buffers work?
-add a little HCl, the salt will react with the H+ (H+ + A- –> HA)
-overall [H+] and pH will remain approximately constant
-add a little -OH, the acid will react with the -OH (HA + -OH –> A- + H20)
-overall the [H+] and pH will remain approximately constant
What happens if you add a little water?
moles of HA and A- remain constant, adding water does not change the moles of HA and A-, so [HA]/[A-] stays the same, so [H+] and pH remain approximately constant
How do alkaline buffers work?
-add a little HCl, the salt will react with the base (H+ + B –> BA)
-overall [H+] and pH will remain approximately constant
-add a little -OH, the salt will react with the -OH (BH + -OH –> B + H20)
-overall the [H+] and pH will remain approximately constant
Test for ammonium ions?
-warm sample with NaOH solution
-NH3 gas produced turns damp red litmus paper blue
