Acid and bases

Frage	Antworten
What is bronsted-lowry acid?	Proton donor
What is bronsted-lowry base?	Proton acceptor
What type of reaction is acid base equilibria?	Neutralisation
What does acid base equilibria involve?	Proton transfer
Define pH.	pH = – log10[H+]
What do the brackets represent?	The concentration
What are the units of concentration?	mol dm-3
How do you convert concentration into pH?	[H+] = 10^-pH
How do you calculate the pH of a solution of a strong acid from its concentration?	pH = – log10[concentration of solution]
What is a strong acid?	Fully ionised in water
How do you calculate the pH for a strong monoprotic acid?	pH = – log10[concentration]
How do you calculate the pH for a strong diprotic acid?	pH = – log10[2x concentration]
How do you calculate the new pH of a strong acid when added to water?	[ H+]new = [ H+]old x old volume/new volume
What is water?	weakly disociated
What equation do you use to work out the Kw (ionic product of water) ?	Kw = [H+][OH– ]
How do you calculate the pH of a strong base from its concentration?	Kw=[H+] [OH-]
What is a strong base?	Fully ionised in solution
How do you work out the pH of a monobasic base?	[OH-]= [base]
How do you work out the pH of a dibasic base?	[OH-]= [2x base]
How do you work out the pH of a diluted strong base?	[ OH-]new = [ OH-]old x old volume/new volume
What steps do you use to work out the pH for the reaction between a strong acid and strong base?	1. Calculate moles of H+ 2. Calculate moles of OH- 3. Calculate moles excess H= or OH- 4. Calculate excess [ H+] or excess [ OH-] 5. Calculate pH
What do weak acid and bases do in water?	Partially dissociate
What is the expression for the dissociation constant Ka for a weak acid?	Ka= [ H+]2/[ HA]
Define pKa.	pKa = – log10 Ka
What is the equivalence point for a reaction between a strong acid and strong base? What indicator should be used?	7 Any indicator can be used.
What is the equivalence point for a reaction between a strong acid and weak base? What indicator should be used?	5 Methyl orange
What is the equivalence point for a reaction between a weak acid and strong base? What indicator should be used?	9 Phenolphthalein
What is the equivalence point for a reaction between a weak acid and weak base? What indicator should be used?	equivalence point can not be accurately detected. Use a pH probe
Why can the equivalence point can not be accurately detected in the reaction between a weak acid and weak base?	The variation in the pH is so gradual.
what are indicators?	Weak organic acids
Define Buffer.	A solution whose pH is resistant to change on the addition of small quantities of acid or base.
What happens to an acidic buffer if acid is added?	H+ combines with A- to from HA. The equilibrium moves to the left to remove the H+. As long as reservoir of A- large enough all the H+ can be removed and the pH is unchanged.
What happens to an acidic buffer if base is added?	OH- combines with H+ to form H2O. This reduces concentration of H+ so more HA will dissociate to replace the H+. Equilibrium will move to the right. As long as reservoir of HA is large enough, all the H+ can be replaced and the pH is unchanged.
What happens to an Basic buffer if acid is added?	Ammonia acts as a sink and mops up proton to form ammonium ions. Equilibrium shifts to the right and as long as there is sufficient NH3 the pH will remain unchanged.
What happens to an Basic buffer if base is added?	Ammonium ions act ac a source of H+ ions and remove the OH- to reform ammonia. Equilibrium shifts to the left and as long as there is sufficient NH4+ the pH will remain unchanged.
How do you calculate the pH of acidic buffer?	[H+] = Ka x [HA]/ [A-] Then use: -log10(H+)
What are examples of buffers?	Organic acids like methanoic acid etc.

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