Acids and bases Flashcards
States the acid, bases, and there conjugates of this equation.
HCl + H2O <=> H3O+ + Cl-
HCl(acid) + H2O(base) <=> H3O+(acid) + Cl-(Base)
State the meaning for pH.
-log10[H+]
State the definition of a Strong Acid.
A Strong Acid completely dissociates into ions in an aqueous solution.
State the definition of a Weak Acid.
A Weak Acid partially dissociates into ions in an aqueous solution and is in equilibrium.
State the definition of a Strong Base.
A Strong Bases completely dissociate into ions in an aqueous solution.
State the definition of a Weak Base.
weak bases partially dissociation react with water to give ions in an aqueous solution.
State the equation for the relative strength of dissociation of a weak acid.
Ka = ([H+][A-]) / ([HA]) pKa = -log10Ka
State the equilibrium which defines the dissociation of a weak acid.
[HA] <=> [H+] + [A-]
State the definition of Kb
The relative strength of dissociation of a base.
State the equilibrium which defines the dissociation of a weak base.
[Base] + [H+] <=> [HB+]
State the definition of the dissociation of water.
H2O <=> H+ + OH-
State the Ionic product of water.
Kw = [H+][OH] at 27oC Kw=10^-14
State one assumption made with Kw.
The concentration of H2O is so large compared to the concentration of [H+] or [OH-] it is regarded as constant combined with kc to make Kw.
What are the units for Kw.
mol2dm-6
State the definition of a neutral solution.
a solution consisting of equal concentrations of H+ and OH- ions.
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 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.
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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.
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Describe an additional way of making a buffer solution
“Adding a measured amount of hydroxide ions to a weak acid
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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]
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“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
