Chemistry- Acids, Bases, and Buffers
pKa=
-log(Ka).
pH=
-log[H+].
The Ionic Product of Water (Kw)=
1 x 10^-14.
What is [H+] When Water Ionises
1 x 10^-7.
How Acidic Materials are Removed From Blood
1. Hydrogen carbonate ions (HCO3-) are converted into carbonic acid (H2CO3). 2. Carbonic acid (H2CO3) is converted into aqueous carbon dioxide through the action of an enzyme. 3. In the lungs, the dissolved CO2 is converted into gaseous CO2 and is exhaled.
What are the Three Methods Used to Prepare a Buffer
1. Mix the weak acid and it's salt e.g. ethanoic acid and sodium ethanoate. 2. Mix the weak acid with a strong base e.g. methanoic acid and sodium hydroxide. 3. Mix a weak acid and a metal e.g. ethanoic acid and sodium.
How to Describe How a Buffer Works
1. Write out the equilibrium for the acid dissociation. 2. Write out the dissociation of the salt. 3. Add acid (H+) and state the equilibrium shift. 4. Write the new equation (with the added H+). 5. Add an alkali (OH-) and state the equilibrium shift. 6. Write the equation of the formation of water from H+ and OH-. 7. Write the new equation (with the added OH-).
How Much Stronger is an Acid of pH 1, Than an Acid of pH 3
100 times stronger.
[H+]=
10^-pH.
Ka=
10^-pKa.
What is the pH Range of Methyl Orange
2.5-4.
What is the pH Range of Bromothymol Blue
6-7.5.
What is the pH of Pure Water at 25°C
7.
What is the path of a healthy Human Blood Plasma
7.35-7.45.
What is the pH Range of Phenylphthalein
8.5-10.
What Must the be for an Acid to Donate Protons
A base must be present to accept the protons.
What is a Strong Base
A base which is fully dissociated in water/solution.
What is a Weak Base
A base which is partially dissociated in water.
When an Acid is Added to it, What Does Water Act As
A base.
What is Blood as a Buffer
A carbonic acid-hydrogen carbonate buffer solution.
What is a Neutralisation Reaction
A chemical reaction in which an acid and base react together to form a salt and water.
What Type of Covalent Bond Does Ammonium Have
A dative covalent bond.
What is a Dibasic/diprotic Acid and Give an Example of One
A dibasic acid e.g. H2SO4 is an acid which has two H+ per molecule.
What is the pH of Blood Controlled By
A mixture of buffers.
What is a Buffer Solution
A mixture that minimises pH changes on the addition of small amounts of an acid or base.
What is a Monobasic Acid and Give an Example of One
A monobasic acid e.g. HCl is an acid which has just one H+ per molecule.
Define Base
A proton acceptor.
Define Acid
A proton donor.
When pKa is Small is it a Strong Weak Acid or a Weak Weak Acid
A strong weak acid.
What is a Tribasic/triprotic Acid and Give an Example of One
A tribasic acid e.g. H3PO4 is an acid which has three H+ per molecule.
Define Alkali
A type of base which dissolves in water to form OH- ions (a soluble base).
What is a Buffer Solution Made From
A weak acid (HA) and a solution of its conjugate base (A-).
What is an Acid-Base Indicator
A weak acid, HIn, which has one colour in acid form (HIn) and another colour in base form (In-).
When pKa is Large is it a Strong Weak Acid or a Weak Weak Acid
A weak weak acid.
What are Most Materials that are Released in the Blood
Acidic.
Acid + NH3 ---->
Ammonium Salt.
What is a Strong Acid and Give an Example
An acid which is completely dissociated in solution, e.g. HCl.
What is a Weak Acid and Give an Example
An acid which is partially dissociated in solution, e.g. ethanoic acid.
When a Base is Added to it, What Does Water Act As
An acid.
When Do a Different Indicators Change Colour
At different pHs.
Why Must a Base be Present to Accept the Protons Given by an Acid
Because H+ ions will accept electrons very strongly, so H+ cannot exist alone in aqueous solutions.
Why is H+ a Proton
Because hydrogen is just one proton and one electron. Take away the electron and you're left with H+.
Why are the Concentrations of Acid and Salt NOT the Concentrations in the Final Buffer
Because the solutions will dilute each other.
Why are the Reactions Between an Acid and a Metal, and Between an Acid and NH3 NOT Neutralisation Reactions
Because water isn't formed.
When Mixing the Weak Acid with a Strong Base or Metal, Why Does the Acid Need to be in Excess
Because you need an acid and a salt for a buffer to be formed. Some of the acid will remain an acid and some will turn to salt, so there's a mixture of acid and salt. If the acid wasn't in excess, there'd only be salt left.
What Colour is Bromothymol Blue When there's More In- than HIn
Blue.
Weak Acid + Salt of the Weak Acid ---->
Buffer Solution.
How Do the Hydrogen Carbonate Ions Remove Acidic Waste From Blood
By being converted into H2CO3.
Because In Equal Concentration Mixtures of Acid and Salt, pH= pKa, the Acid Chosen to Make a Buffer Must Have a pKa Which is, What (and Why)
Closest to the required pH. This is because it will lead to a mixture of acid and salt closest to the 1:1 ratio.
What Colour is Phenylphthalein When there's More HIn than In-
Colourless.
What is the Dissociation of (the Ions of) a Weak Acid In
Equilibrium.
What Colour is Bromothymol Blue When there's Equal Amounts of HIn and In-
Green.
When Ka is Large is it a Strong Weak Acid or a Weak Weak Acid and Why
If Ka is large, there's more [H+] than [HA] so there's a large extent of dissociation, so it's a strong weak acid.
When Ka is Small is it a Strong Weak Acid or a Weak Weak Acid and Why
If Ka is small, there's more [HA] than [H+] so there's a small extent of dissociation, so it's a weak weak acid.
Where, Typically, is the End Point of an Indicator
In he middle of the pH range.
What is a Species Split into if it's Aqueous
Ions.
What Colour is Phenylphthalein When There's Equal Amounts of HIn and In-
It's palest pink.
Give an Example of a Weak Base
NH3.
Give Two Examples of Strong Bases
NaOH and Ca(OH)2.
Give Five Examples of Strong Acids
Nitric acid (HNO3), sulphuric acid (H2SO4), hydrobromic acid (HBr), hydroiodic acid (HI), and chloric (VII) acid (HClO4).
What Colour is Methyl Orange When there are Equal Amounts of HIn and In-
Orange.
Give Two Examples of Weak Acids
Organic acids, and methanoic acid.
What Colour is Methyl Orange When there's More In- than HIn
Pink.
What Colour is Methyl Orange When there's More HIn than In-
Red.
Acid + Insoluble Carbonate ---->
Salt + CO2 + H2O.
Acid + Soluble Carbonate ---->
Salt + CO2 + H2O.
Acid + Metal ---->
Salt + H2.
Acid + Alkali ---->
Salt + H2O.
Acid + Insoluble Base ---->
Salt + H2O.
Why Must a Particular Indicator Be Used for a Certain Titration
So that the pH at the end point is as close to the pH value of the titrations' equivalence point.
In What Physical States is a Species NOT Split into Ions
Solid, liquid, or gas.
What Does pH Being a -log Scale Mean
That a low pH means there's a high H+ concentration and a high pH means there's a low H+ concentration.
What Does Aqueous (aq) Mean
That something is dissolved in water.
What Does the pH of a Buffer Solution Depend On
The Ka of the weak acid and the acid:salt ratio.
What Does Kw Control
The balance between [H+] and [OH-].
What is the Most Important Ion in Controlling the pH of Blood
The carbonic acid-hydrogen carbonate ion.
What is Kw
The ionic product of water.
What is the Equivalence Point
The point in a titration at which the volume of one solution has exactly reacted with the volume of the second reactant.
What is he End Point
The point in a titration at which there are equal concentrations of e weak acid and conjugate base forms of the indicator.
What is the Amount of CO2 in the Blood be Controlled By
The rate of breathing e.g. heavy breathing will remove ore CO2.
What is Low When the Value of Ka is High
The value of pKa.
When Two Acids are Reacted Together, Which One Acts as a Base
The weaker acid.
Why Do a Lot of Biological Systems Contain Buffer Solutions
They are very pH sensitive, so need to be kept at their optimum pH.
Define a Conjugate Acid-Base Pair
This is a pair of two species that transform into each other by the gain or loss of a proton.
What is Acidosis
This is when the pH of blood plasma is below 7.35.
What is Alkalosis
This is when the pH of blood ppqs a is above 7.45.
What Do Acid-Base Equilibria Involve
Two acid-base pairs.
When Should you Take Account of Dilutions
When buffers are made by mixing solutions.
Define Amphoteric
When something, e.g. water, can act as an acid or a base.
Where on a Titration Curve will a Suitable Indicator Change Colour
Within the pH range of the vertical section of her titration curve.
What Colour is Bromothymol Blue When there's More HIn than In-
Yellow.
What Colour is Methyl Orange When there's More In- than HIn
Yellow.
In an Alkali, What is the Balance Between [H+] and [OH-]
[H+] < [OH-].
At pH 7, What is the Balance Between [H+] and [OH-]
[H+] = [OH-].
In an Acid, What is the Balance Between [H+] and [OH-]
[H+] > [OH-].
In Weak Acids, What Does [HA] NOT Equal
[H+].
What Does [HA] Equal in a Strong Acid
[H+].
Ka=
[H+][A-]/[HA].
Kw=
[H+][OH-].
When Water Ionises, [H+]=
[OH-].
What are the Units of Kw
mol^2dm^-6.
What are the Units for Ka
moldm^-3.
In Equal Concentration Mixtures of Acid and Salt, pH=
pKa.