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14 Cards in this Set
- Front
- Back
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What is a buffer solution? |
A solution which minimises change of ph when small amounts of acid or alkali are added |
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What do buffer solutions consist of? |
A weak acid and it’s conjugate base |
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What do the components of buffer solution do? |
Weak acid removes the added base Conjugate base removes the added acid |
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What happens to the ability of the buffer solution when acid or bases are added? |
Loses it ability when one of the components gets used up |
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Explain the action of a buffering solution |
Conjugate base removes the added acid: •[H+] increases •[H+] reacts with base •position of equilibrium moves to the left so more [HA] is made which decreases [H+] and therefore decreases acidity Weak acid removes the added base: •[OH-] increases •reacts with [H+] and forms water •more [HA] is made so equilibrium shifts to the right so more [h+] is made, decreasing alkalinity |
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What are the three methods that can be used to prepare a buffer solution? |
Method 1: •mix solution of ethanoic acid and it’s salt •when ethanoic acid is added to water, it partially dissociates so acts as a weak acid of the buffer solution •when the salt is added, it dissolved and dissociates so salt acts as a conjugate base Method 2: •add solution of Aqueous solution of alkaline (Naoh) to excess of weak acid •weak acid is partially neutralised by the alkaline forming a conjugate base Method 3: •in ethanoic acid equilibrium, position of equilibrium is towards the acid. •when ch3coo- ions are added, equilibrium shifts further towards acid leaving a small conc of h+ ions and mostly the ethanoic acid and it’s salt which act as a weak acid and conjugate base of a buffer solution |
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How do we know which weak acid to use? |
A buffer is most effective when concentrations of weak acid and base are the same. Ph of buffer solution is equal to Pka value of (ha) •operating ph range will be over two units of the pka valhe |
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What is the equation of calculating ph of buffer solution? |
H+= ka x ha/a- |
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Explain the carbonic acid / hydrogen carbonate buffer system in the human body |
In addition of acid: •h+ concentration increases •reacts with conjugate base •equilibrium shifts to the left to decrease h+ concentration In addition of alkaline •oh conc increases •reacts with h+ and forms water •carbonic acid dissociates •equilibrium shifts to the right so more h+ is made |
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Outline the method for measuring ph of acid base titration |
•add known volume of acid to conical flask •dip electrode of ph meter into acid solution and record ph •add base to burette and slowly add base to acid solution, 1cm3 at a time and record ph •keep adding base until there is no change in ph |
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Describe the shape of acid base titration curve |
•slowly ph increases because acid is in excess •towards vertical section, ph changes as acid is being used up •vertical section is when ph changes rapidly •after vertical section, ph changes slowly as base is now in excess |
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What is the equivalence point? |
Volume of solution that exactly reacts with another Found in centre of vertical section |
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What is the equivalence point? |
Volume of solution that exactly reacts with another Found in centre of vertical section |
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What are indicators? |
Weak acids used to see when the end point of a reaction is At the end point, indicator contains equal conc of base and acid and colour will be in between both extreme colours |
