Chapter 8 Test Flashcards
How do you answer the questions asking you about changing volumes of a solution?
You will try to always change it to a multiple of 10
What pH are bases?
Anything greater than 7
What pH are acids?
Anything less than 7
The smaller the _______, the larger the _________, the weaker the acid/base.
Ka/Kb, pKa/pKb
How would you determine the concentration of an acid by using the base’s equivalence point on a titration curve?
Multiply the mL/L of the equivalence volume times the concentration of the base times the mole ratio between the two(acid and base). Then divide the moles by the volume of the acid.
How do you solve equations with a weak acid and a strong base if the weak acid is in excess?
- Same goes for weak base/strong acid
The resulting solution is a buffer. So use the Henderson-Hasselbach equation to determine the pH.
What does a strong acid/strong base titration curve look like?
Its equivalence point is at a pH of 7. If a base is being added to an acid that will affect the shape also.
What can you remember about monoprotic strong acids and their concentrations?
The concentration of the acid is equal to the concentration of the hydronium ions
How do you solve equations with a weak acid and a weak base?
They will go to equilibrium so you use ice tables
Titrant
The solution with the known concentration in the burette
Is Ka or pKa often used for weak acids?
pKa
How do you write dissociation equations?
Acid + Water yields conjugate base and hydronium
Base + Water yields conjugate acid and hydroxide
When should you use a single arrow? What about double arrows?
Single arrows for anything strong because it completely dissociates
Double arrows if there are two weak things
If the same acid has two different concentrations, the solution of lower concentration will have a ________ percent ionization.
Higher
What is the pH of water and what happens to the pOH?
They are both 7 because pure water is neutral, however, if the temperature is not 25 degrees celsius then you know pH and pOH will always be the same
Analyte
The solution with the unknown concentration in the beaker
What do the values generally look like for Ka/Kb values of weak acids/bases?
The values are smaller than 1 because these reactions do not go to completion
How do you solve equations for weak acids? For strong acids?
You need an ice table; You can just do the equations on the equation sheet
Acid
Donates hydrogen ions
What do the values generally look like for Ka/Kb values of strong acids/bases?
The values are larger than 1 because these reactions go to completion
How do weak acids often look in particle diagrams?
Unionized, mainly reactants because they didn’t dissociate completely
The smaller the _______, the larger the _________, the stronger the acid/base.
pKa/pKb, Ka/Kb
Base
Receives hydrogen ions
What should you remember when writing net ionic equations with strong bases or acids?
The part that isn’t H+ or OH- is a spectator ion. Remember to just leave that part out when writing the net ionic equation
What is happening when an indicator changes color?
It is the end point of the titration. The moles of acid and base should be basically equal
What is an easy way to constitute a weak base?
If something does not have a hydroxide
How does the strength of an acid determine the strength of its conjugate base?
The stronger an acid is, the weaker its conjugate base will be
Buffering region
This is on a titration curve where the pH of a solution doesn’t change much
If acids are of equal concentration, the weaker acid will have a ________ percent ionization.
Lower
Percent Ionization
How much an acid ionizes; a strong acid will have 100% ionization
How do you write an equilibrium constant?
Don’t include any liquids or solids and it is products over reactants
Equivalence Point
When the moles of acid and moles of base are equal. When all the initial material was consumed
What does an equivalence point look like on a titration curve?
It is the steepest point and the largest slope
What does a weak acid(base)/strong base(acid) titration curve look like?
The pH is going to be above or below 7 not right at it. Also, the pKa is going to be the pH at 1/2 the equivalence volume. Also, there will be a buffering region on the graph
What is the only thing that can affect a K value?
Temperature changes
What is true of the concentrations at the 1/2 equivalence point?
The concentrations of the acid and its conjugate base are equal
Percent Ionization Formula
[hydronium ion] at equilibrium/ [acid] initial times 100
What is the pH of something neutral?
7
Why would a strong acid have a smaller pH than a weak acid?
Because strong acids dissociate completely and create higher concentrations of H+
What do polyprotic acid titration curves look like?
They have multiple equivalence points/steep parts of their graphs.
What should you remember when writing net ionic equations for weak bases and acids?
They don’t have spectator ions
The higher the concentration of H+, the more ________ the pH is.
Acidic
How do you go from pH to [H+]?
10^-pH
How do you solve equations with a strong acid and a strong base?
1) Find the moles of each
2) Discover what is the limiting reactant (whatever is smaller)
3) Then, subtract both moles by the limiting reactant’s moles
4) Then divide the leftover excess reactant’s moles by the total volume(additive) to find the molarity of the resulting solution
What are the main characteristics of strong acids and bases?
They are strong electrolytes and they conduct electricity easily. Also, they dissociate completely
How do you solve equations with a weak acid and a strong base if the strong base is in excess?
- Same goes for weak base/strong acid
Divide the leftover excess reactant’s moles by the total volume(additive) to find the molarity of the resulting solution
What do you have to remember when finding concentrations?
Volume is additive
Why does a conjugate of a strong acid have no or limited basic properties?
Because they are very stable; they are really electronegative and can pull electrons to stabilize themselves, they have inductive effects and can stabilize themselves well due to how their electrons are distributed, and they can have resonance which increases the stability because the negative charge of this conjugate base is spread out.
How do bond lengths and strength play a part in the strength of an acid?
The longer and weaker a bond is the stronger the acid because a strong acid easily dissociates so the weaker a bond is the easier it is for it to dissociate
So remember as you go down a column in the periodic table the atomic radius gets larger which results in a longer bond
How do oxyacids relate to acid strength?
The more oxygens you have in an acid, the stronger the acid is because increasing oxygen atoms increasing resonance which increases stability of the conjugate base.
How does electronegativity relate to acid strength?
The more electronegative an atom is the better it is at pulling electrons toward itself meaning this will weaken the H-O bond and help that proton break off easier which means the acid is stronger
How does electronegativity relate to base strength?
The more electronegative an atom is the weaker a base is because the more electronegative an atom is the better it is at pulling electrons toward itself meaning this will weaken the H-O bond and help that proton break off easier however a base is a proton acceptor and a very electronegative atom will take away the base’s needed protons
What are carboxylic acids? Explain their importance.
This is when a carbon is double bonded to an oxygen and single bonded to another oxygen. The single bonded oxygen also has an H+ attached to it.
The double bonded oxygen in the carboxylic acid is very electronegative and pulls electrons towards itself which weakens that O-H bond and helps the H+ donate itself easily making the acid stronger. Also, its conjugate, the carboxylate ion, can spread its negative charge between the two ions making it more stable due to its resonance which ultimately makes the acid stronger because it is not trying to “snatch” the H+ back.
What type of acids are H with N, O, or F?
They are all weak acids because these types of acids have hydrogen bonding which is strong and hard to break apart so the acids are weak and do not completely dissociate
What can we assume when the pH is less than the pKa?
That the conjugate base/strong acid ratio is less than one, meaning there is more strong acid than conjugate base.
What can we assume when the pH is greater than the pKa?
That the conjugate base/strong acid ratio is grater than one, meaning there is more conjugate base than strong acid
When do color changes typically occur?
1 pH unit above and below the pKa
What is an estimate of the pH when you mix a strong base and a weak acid?
It will be greater than 7
What is an estimate of the pH when you mix a strong acid and a weak base?
It will be less than 7
Buffer
A solution that contains a conjugate-acid base pair. They maintain the pH of a solution when small amounts of acids or bases are added to the solution. They do not contain any strong acids or bases.
How would a buffered solution react to an acid being added?
The solution will turn to its acidic form because it will react with the base in the solution
How would a buffered solution react to a base being added?
The solution will turn to its basic form because the base will react with the acid in the solution
How do you answer the buffer questions?
Make an ice table with the strong acid/base, and the weak acid/base and its conjugate pair.
