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Acid-Base Equilibria

AQA A Level Chemistry

QuestionAnswer
What are the Bronsted Lowery definitions of an acid and a base? An Acid is a proton donor and a Base is a proton acceptor
What is the conjugate acid of NH3? NH4+
What is the conjugate base of CH3COOH? CH3COO-
What is the conjugate acid of HNO3? H2NO3+
Names the Acid Base conjugate pairs in this reaction H3O+ + HSO4- → H2SO4 + H2O H3O+ Acid H2O Base. HSO4- Base H2SO4 acid.
Give the formula of Hydroxonium Ion H3O+
Describe the bonding in the Hydroxonium Ion Covalent and Dative Covalent Bonding
Define a strong acid An acid that completely dissociates in aqueous solution
Define a weak acid An acid that partially dissociates in aqueous solution.
What is the general formula for the acid dissociation constant? Ka= [H+][A-]/ [HA]
What is the definition of pH? pH= -log10[H+(aq)]
What is the pH of a solution with a [H+] of 1.23x10-4 mol dm-3 3.91
What is the pH of a solution with a [H+] of 7.89 x10-15 mol dm-3 14.1
Rearrange the definition of pH to make [H+(aq)] the subject [H+(aq) = 10-pH
What is the [H+(aq)] of a solution with a pH of 9.2? 6.31x10-10 moldm-3
Calculate the pH of the solution formed by adding of 250 cm3 of water to 50 cm3 of 0.200 mol dm-3 HNO3 1.48
Calculate the pH of the following solution 100 g dm-3 H2SO4 -0.31
What is the formula of the ionic prodcut of water Kw Kw = [H+][OH-]
What is the relationship between pH and pOH? pH + pOH = 14
Calculate the pH of the following solution: 0.20 mol dm-3 Ba(OH)2 13.6
Calculate the pH of the solution formed by the addition of 100 cm3 of water to 25 cm3 of 0.100 mol dm-3 NaOH 12.3
Write a general equation for the dissociation of a weak acid "HA(aq) → A¯(aq) + H+(aq)
What are the two assumptions one makes when calculating the pH of a weak acid? "The amount of HA at equilibrium is equal to the amount of HA put into the solution and [H+(aq)]= [A¯(aq)]
What does the general formula for the acid dissociation constant become when these two assumptions are applied? "Ka = [H+(aq)]2/[HA(aq)]
Write the fomula you use to calculate the pH of a weak acid. [H+(aq)] = √ [HA(aq)] Ka
Calculate the pH of the following weak acid: 0.200 mol dm-3 butanoic acid (Ka = 1.51 x 10-5 mol dm-3) 2.76
Calculate the Ka value for phenylethanoic acid given that a 0.100 mol dm-3 solution has a pH of 2.66 4.79 x 10-5 mol dm-3
Write the seven steps for the calculation of the pH of a solution formed by the reactions between a weak acid and a strong base if the acid is in excess. Calculate moles HA (it is still HA and not H+ as it is a weak acid), Calculate moles OH, Calculate moles XS HA, Calculate moles HA left and A- formed, Calculate [HA] leftover and [A-] formed, Use Ka to find [H+], Find pH
Write the six steps for the calculation of the pH of a solution formed by the reactions between a weak acid and a strong base if the OH- is in excess. Calculate moles HA (it is still HA and not H+ as it is a weak acid), Calculate moles OH, Calculate moles XS OH, Calculate [OH-], Use Kw to find [H+], Find pH
Calculate the pH of the solution formed when 50 cm3 of 0.500 mol dm-3 ethanoic acid (pKa = 4.76) is added to 50 cm3 of 0.250 mol dm-3 KOH 4.76
What is a titration? " a solution of accurately known concentration is added gradually added to another solution of unknown concentration until the chemical reaction between the two solutions is complete.
What is the equivalence point of a titration? "the point at which the titration reaction is complete
Define what types of substances are suitable to be indicators They are weak acids whose conjugate base is a different colour to the acid.
How do you select a suitable indicator for a particular type of titration. The pH range of the suitable indicator fits within the vertical section of the titration curve.
"Methyl Orange has a pH range of 3.1-4.4 for what types of titration Is it suitable? Strong acid, Strong base. Strong acid, Weak Base
"Phenolpthalein has a pH range of 8.3-10.0 for what types of titration Is it suitable? Strong acid, Strong base. Weak acid, Strong Base
What is the typical equivalence point of a strong acid strong base titration? 7
What is the typical equivalence point of a strong acid weak base titration? 5
What is the typical equivalence point of a weak acid strong base titration? 9
What is the typical pH range of the vertical section of a strong acid strong base titration curve? 3 to 10
What is the typical pH range of the vertical section of a weak acid strong base titration curve? 7 to 11
What is the typical pH range of the vertical section of a strong acid weak base titration curve? 3 to 7
Explain how one can use a titration curve to calculate Ka of a weak acid. "Half way to the equivalence point [HA(aq)] = [A¯ (aq) ], so pKa = pH
Define what is a buffer solution "Solutions which resist changes in pH when small quantities of acid or alkali are added.
Describe the most common way of making a buffer solution. "A buffer solution is made from a weak acid and the salt of the weak acid.
Describe an additional way of making a buffer solution "Adding a measured amount of hydroxide ions to a weak acid
What are the two assumption we make when calculate the pH of a buffer solution. "All the A- ions come from the salt, Almost all the HA molecules put into the buffer remain unchanged
What does the general formula for the acid dissociation constant become when the assumptions for a buffer solution are applied? " Ka = [H+(aq)] x [salt]/ [acid]
"What happens if an acidic substance is added to a buffer? " "Any rise in [H+(aq)] disturbs the equilibrium. Some A-(aq) ions from the salt react with the extra H+(aq) ions to form HA(aq) and water. A significant fall in pH is prevented.
Calculate the pH of the following buffer solutions made by mixing 50.0 cm3 of 1.00 mol dm-3 methanoic acid (Ka = 1.78 x 10-4 mol dm-3 with 20.0 cm3 of 1.00 mol dm-3 sodium methanoate 3.35
"Calculate the pH of the following buffer solution made by mixing 100 cm3 of 1.00 mol dm-3 ethanoic acid (Ka = 1.78 x 10-4 mol dm-3 ) is mixed with 50.0 cm3 of 0.8000 mol dm-3 sodium hydroxide. " 3.57
Created by: JBearfield
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