5.3 Acids, Bases and pH Flashcards
What are acids ?
They dissociate H+ ions into an aqueous solution.
What are bases ?
They dissociate and release OH- ions into an aqueous solution.
What is ionic equation for water ?
H+ + OH- = H2O
Are alkalis a soluble base ?
Yes
What is a Bronsted-Lowry acid described as ?
Acid that acts as a proton donor.
What is a Bronsted-Lowry base described as ?
Base that acts as a proton acceptor.
What is a conjugate acid-base pair ?
Contains 2 species that can be interconverted by the transfer of a proton between the acid and base.
What is the acid base equation for the hydronium ion ?
HCl + H2O = H3O+ + Cl-
A1 B2 A2 B1
What does a mono basic, dibasic and tribasic acid refer to ?
Refers to the total number of hydrogen ions in the acid that can be replaced per molecules in an acid-base reaction.
What is the reaction with an acid and a metal ?
Acid + metal = salt + hydrogen
What is the ionic equation equation for the reaction between an acid and a metal ?
2H+ + Mg = Mg2+ + H2
What is the reaction with an acid and a carbonate ?
Acid + carbonate = salt + water + carbon dioxide
What is the ionic equation for the reaction with an acid and a carbonate ?
2H+ + CO3 = Cu2+ + H2O + CO2
What is the reaction with an acid and a metal oxide ?
Acid + metal oxide = salt + water
What is the ionic equation with an acid and a metal oxide ?
2H+ + MgO = Mg2+ + H2O
What is the reaction of an acid with an alkali ?
Acid + alkali = salt + water
What is the ionic equation of the reaction of an acid with an alkali ?
H+ + OH- = H2O
What value of pH does a low value of H+ ions show ?
High pH value.
What value of pH does a high value of H+ ions show ?
Shows a low pH.
How do you work out pH using logarithms ?
pH = -log [ H+ ]
How do you work out H+ ions concentration if you are given the pH ?
[H+] = 10* -pH
What does a change in one pH number equal to in difference in H+ ions ?
Equal to 10x the difference in H+ ion concentration, so there is a large difference in hydrogen ion concentrations between pH 2 and pH 3.
What is a strong acid ?
Acid that fully dissociates all of its H+ ions into an aqueous solution.
What is a weak acid ?
Acid that partially dissociated some of its H+ ions into an aqueous solution.
In a strong acid, what is the concentration of H+ ions equal to ?
[H+] = [HA]
So, pH of a strong acid can be calculated directly from the concentration of the acid.
What is the acid dissociation constant, Ka ?
For any weak acid,
Ka = [H+] [A-] / [HA] mol dm-3
Where does the equilibrium lie if there is a large value of Ka ?
The larger the value of Ka, the further the equilibrium lies to the right. Larger value means the greater dissociation and the greater the acid strength.
What is pKa ?
pKa = -log (Ka)
How do you work out Ka from pKa ?
Ka = 10* -pKa
What effects does a strong acid have on Ka and pKa value ?
Stronger the acid, the larger the Ka value and the smaller the pKa value.
What effect does a weak acid have on Ka and pKa value ?
The weaker the acid, the smaller the Ka value and the larger the pKa value.
For weak acids, why is [H+] = [A-] in an equilibrium ?
HA dissociates to produce equilibrium concentrations of H+ and A- that are equal. There will also be a very small concentration of H+ from the dissociation of water but this will be extremely small and can be neglected compared with the H+ concentration from the acid.
For weak acids, why is [HA]eqm = [HA]start - [H+]eqm ?
Concentration of HA is smaller than the undissociated concentration. As the dissociation is small, you can assume that [HA] at start is greater than [H+] and you can neglect any decrease in the concentration of HA from dissociation.
What is the simplified Ka equation ?
Ka = [H+]*2 / [HA]
How can you calculate pH from H+ concentration ?
[H+] = square root of Ka x [HA]
-log [H+] = pH
What is the ionisation of water ?
H20 + H20 = H3O+ + OH-
Acts as both an acid and a base, setting up the acid-base equilibrium.
What is Kw ?
Is the ionic product of water, the ions in the water are multiplied together. Kw also varies with temperature.
What is the equation for Kw ?
Kw = [H+] [OH-]
Why is Kw important ?
Significance of having Kw at 1.00 x10*-14 at 25C means that the value sets up the neutral point in the pH scale. On dissociation it is neutral so produces same number of H= and OH- ions.
According to Kw, what makes an aqueous solution acidic, neutral or alkaline ?
[H+] > [OH-]
[H+] = [OH-]
[H+] <[OH-]
How do you calculate the pH of a strong base ?
Find [OH-]
Find [H+] using Kw and [OH-]
-log [H+] to find pH.
What is pOH ?
Used as a convenient way to show [OH-].
pOH = -log [OH-]
[OH-] = 10* -pOH
