Post on 25-Feb-2016
description
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Equilibria seminar
University of Lincoln presentation
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Le Chatelier’s PrincipleWhen an external change is made to a system in equilibrium, the
system will respond to oppose the change1. BiCl3(aq) + H2O(l) ↔ BiOCl(s) + 2HCl(aq)
2. Cr2O72-(aq) + 2OH-(aq) ↔ 2CrO4
2-(aq) + H2O(l)
How does reaction 1 respond to addition of hydrochloric acid?How does reaction 2 respond to addition of alkali?How does reaction 2 respond to addition of acid?
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N2(g) + 3H2(g) ↔ 2NH3(g)CO(g) + 2H2(g) ↔ CH3OH(g)2NO2(g) ↔ 2NO(g) + O2(g)PCl5(g) ↔ PCl3(g) + Cl2(g)H2(g) + I2(g) ↔ 2HI(g)CO(g) + H2O(g) ↔ CO2(g) + H2(g)How do the above equilibria respond to:An increase in pressureA decrease in pressure
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N2(g) + 3H2(g) ↔ 2NH3(g) rH = -92.2 kJ mol-1
H2(g) + I2(g) ↔ 2HI(g) rH = -9.4 kJ mol-1
CO(g) + H2O(g) ↔ CO2(g) + H2(g) rH = -41.2 kJ mol-1
PCl5(g) ↔ PCl3(g) + Cl2(g) rH = 87.9 kJ mol-1
How do the above respond to anIncrease in temperatureDecrease in temperature
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CH3COOH (aq) + H2O(l) ↔ H3O+ (aq) + CH3COO-
(aq)
• CH3COOH: CH3COO- at pH = 4.77 ?• CH3COOH: CH3COO- at pH = 3 ?• CH3COOH: CH3COO- at pH = 7 ?
ionised][un[ionised]logpKpH a
pKa= 4.77
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CH3NH2(aq) +H2O(l) ↔ CH3NH3+
(aq) + OH-(aq)
pKa = 10.66 (of conjugate acid) pH = 10.66 [B]=[BH+]pH =8 what happens to CH3NH3
+(aq): CH3NH2(aq)
pH =13 ?
][][log
ionisedionisedunpKpH a
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Acidic drugs
How does this molecule ionise?pKa=4.5pH =3 (stomach pH)?pH=6 (intestine)?
ibuprofenCH3
CH3
CH3
O-
O
H+
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amphetamine (C6H5CH2CH(NH2)CH3)Write an equation for the reaction of
amphetamine with water.The pKa of the conjugate acid is 9.8. What
will happen to the ratio of ionised to unionised amphetamine at:
pH 7pH 12Why might this be important?
Basic drugs CH3
NH3+
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Making a buffer solution• Choose a weak acid with a pKa close to
the required pH of the buffer.• Choose an appropriate salt of the weak
acid• Determine [salt]/[acid] ratio needed to
give correct pHWhat would be the pH of an ethanoate
buffer with equal acid and sodium ethanoate concentrations?
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Acid pKa Conjugate base
H3PO4 2.12 H2PO4-
HNO2 3.34 NO2-
H2CO3 6.37 HCO3-
HCN 9.31 CN-
HCO3- 10.25 CO3
2-
pKa values (data tables)
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[acid][salt]logpKpH a
04.77pH
pH = 5pH = 4
Ethanoate buffers
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Acknowledgements• JISC• HEA• Centre for Educational Research and
Development• School of natural and applied sciences• School of Journalism• SirenFM• http://tango.freedesktop.org